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− | ===2.1 Introduction===
| + | The contact parts are important components in switching devices. They have to maintain their function from the new state until the end of the functional life of the devices. |
− | The contact parts are important components in switching devices. They have to | |
− | maintain their function from the new state until the end of the functional life of the | |
− | devices. | |
| | | |
− | The requirements on contacts are rather broad. Besides typical contact properties | + | The requirements on contacts are rather broad. Besides typical contact properties such as |
− | such as | |
| | | |
| *High arc erosion resistance | | *High arc erosion resistance |
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| *Good arc extinguishing capability | | *Good arc extinguishing capability |
| | | |
− | they have to exhibit physical, mechanical, and chemical properties like high electrical
| + | They have to exhibit physical, mechanical and chemical properties like high electrical and thermal conductivity, high hardness, high corrosion resistance etc. and besides this, should have good mechanical workability and also be suitable for good weld and brazing attachment to contact carriers. In addition they must be made from environmentally friendly materials. |
− | and thermal conductivity, high hardness, high corrosion resistance, etc and besides | |
− | this should have good mechanical workability, and also be suitable for good weld and | |
− | brazing attachment to contact carriers. In addition they must be made from | |
− | environmentally friendly materials. | |
| | | |
− | Materials suited for use as electrical contacts can be divided into the following groups | + | Materials suited for use as electrical contacts can be divided into the following groups based on their composition and metallurgical structure: |
− | based on their composition and metallurgical structure: | |
| | | |
| *Pure metals | | *Pure metals |
| *Alloys | | *Alloys |
| *Composite materials | | *Composite materials |
− | *Pure metals
| |
| | | |
− | From this group silver has the greatest importance for switching devices in the higher
| |
− | energy technology. Other precious metals such as gold and platinum are only used in
| |
− | applications for the information technology in the form of thin surface layers. As a nonprecious
| |
− | metal tungsten is used for some special applications such as for example as
| |
− | automotive horn contacts. In some rarer cases pure copper is used but mainly paired
| |
− | to a silver-based contact material.
| |
| | | |
− | *Alloys
| + | '''Pure metals''' |
| + | |
| + | Within this group, silver has the greatest importance for switching devices in the higher energy technology. Other precious metals such as gold and platinum are only used in applications for the information technology in the form of thin surface layers. As a nonprecious metal, tungsten is used for some special applications such as, for example, automotive horn contacts. In some rarer cases, pure copper is used, but mainly paired to a silver-based contact material. |
| + | |
| + | '''Alloys''' |
| + | |
| + | Besides these few pure metals, a larger number of alloy materials made by melt technology are available for the use as contacts. An alloy is characterized by the fact, that its components are completely or partially soluble in each other in the solid state. Phase diagrams for multiple metal compositions show the number and type of the crystal structure as a function of the temperature and composition of the alloying components. |
| | | |
− | Besides these few pure metals a larger number of alloy materials made by melt
| + | They indicate the boundaries of liquid and solid phases and define the parameters of solidification. |
− | technology are available for the use as contacts. An alloy is characterized by the fact
| + | Alloying allows to improve the properties of one material at the cost of changing them for the second material. As an example, the hardness of a base metal may be increased while at the same time the electrical conductivity decreases with even small additions of the second alloying component. |
− | that its components are completely or partially soluble in each other in the solid state.
| |
− | Phase diagrams for multiple metal compositions show the number and type of the
| |
− | crystal structure as a function of the temperature and composition of the alloying components.
| |
| | | |
− | They indicate the boundaries of liquid and solid phases and define the
| + | '''Composite Materials''' |
− | parameters of solidification.
| |
− | Alloying allows to improve the properties of one material at the cost of changing
| |
− | them for the second material. As an example, the hardness of a base metal may
| |
− | be increased while at the same time the electrical conductivity decreases with
| |
− | even small additions of the second alloying component.
| |
| | | |
− | *Composite Materials
| + | Composite materials are a material group whose properties are of great importance for electrical contacts that are used in switching devices for higher |
| + | electrical currents. |
| | | |
− | Composite materials are a material group whose properties are of great
| + | Those used in electrical contacts are heterogeneous materials, composed of two or more uniformly dispersed components, in which the largest volume portion consists of a metal. |
− | importance for electrical contacts that are used in switching devices for higher
| |
− | electrical currents.
| |
− | Those used in electrical contacts are heterogeneous materials composed of two | |
− | or more uniformly dispersed components in which the largest volume portion | |
− | consists of a metal. | |
− | The properties of composite materials are determined mainly independent from
| |
− | each other by the properties of their individual components. Therefore it is for
| |
− | example possible to combine the high melting point and arc erosion resistance
| |
− | of tungsten with the low melting and good electrical conductivity of copper, or
| |
− | the high conductivity of silver with the weld resistant metalloid graphite.
| |
| | | |
− | Figure 2.1 shows the schematic manufacturing processes from powder
| + | The properties of composite materials are determined mainly independent from each other by the properties of their individual components. Therefore it is, for example, possible to combine the high melting point and arc erosion resistance of tungsten with the low melting and good electrical conductivity of copper or the high conductivity of silver with the weld resistant metalloid graphite. <xr id="fig:Powder metallurgical manufacturing of composite materials (schematic)"/> shows the schematic manufacturing processes from powder blending to contact material. Three basic process variations are typically applied: |
− | blending to contact material. Three basic process variations are typically | |
− | applied: | |
| | | |
| *Sintering without liquid phase (Press-Sinter-Repress, PSR) | | *Sintering without liquid phase (Press-Sinter-Repress, PSR) |
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| *Infiltration (Press-Sinter-Infiltrate, PSI) | | *Infiltration (Press-Sinter-Infiltrate, PSI) |
| | | |
− | During sintering without a liquid phase (left side of schematic) the powder mix is
| + | <figure id="fig:Powder metallurgical manufacturing of composite materials (schematic)"> |
− | first densified by pressing, then undergoes a heat treatment (sintering), and
| + | [[File:Powder metallurgical manufacturing of composite materials (schematic).jpg|thumb|<caption>Powder-metallurgical manufacturing of composite materials (schematic) T<sub>s</sub> = Melting point of the lower melting component)</caption>]] |
− | eventually is re-pressed again to further increase the density. The sintering
| + | </figure> |
− | atmosphere depends on the material components and later application; a
| |
− | vacuum is used for example for the low gas content material Cu/Cr. This
| |
− | process is used for individual contact parts and also termed press-sinterrepress
| |
− | (PSR). For materials with high silver content the starting point at | |
− | pressing is most a larger block (or billet) which is then after sintering hot
| |
− | extruded into wire, rod, or strip form. The extrusion further increases the density
| |
− | of these composite materials and contributes to higher arc erosion resistance.
| |
− | Materials such as Ag/Ni, Ag/MeO, and Ag/C are typically produced by this
| |
− | process.
| |
| | | |
− | Sintering with liquid phase has the advantage of shorter process times due to
| + | During ''sintering without a liquid phase'' (left side of schematic), the powder mix is first densified by pressing, then undergoes a heat treatment (sintering) and eventually is re-pressed again to further increase the density. The sintering atmosphere depends on the material components and later application; a vacuum is used for example for the low gas content material Cu/Cr. This process is used for individual contact parts and also termed press-sinter-repress (PSR). For materials with high silver content, the starting point before pressing is mostly a large block (or billet) which is then, after sintering, hot extruded into wire, rod or strip form. The extrusion further increases the density of these composite materials and contributes to higher arc erosion resistance. Materials such as Ag/Ni, Ag/MeO and Ag/C are typically produced by this process. |
− | the accelerated diffusion and also results in near-theoretical densities of the | |
| | | |
− | Fig. 2.1: Powder-metallurgical manufacturing of composite materials (schematic)
| + | ''Sintering with liquid phase'' has the advantage of shorter process times due to the accelerated diffusion and also results in near-theoretical densities of the composite material. To ensure the shape stability during the sintering process, it |
− | T = Melting point of the lower melting component
| |
− | | |
− | composite material. To ensure the shape stability during the sintering process it | |
| is however necessary to limit the volume content of the liquid phase material. | | is however necessary to limit the volume content of the liquid phase material. |
| | | |
− | As opposed to the liquid phase sintering which has limited use for electrical | + | As opposed to the liquid phase sintering, which has limited use for electrical contact manufacturing, the ''Infiltration process'' as shown on the right side of the schematic, has a broad practical range of applications. In this process the powder of the higher melting component, sometimes also as a powder mix with a small amount of the second material, is pressed into parts. Then, right after sintering, the porous skeleton is infiltrated with liquid metal of the second material. The fill-up process of the pores happens through capillary forces. This process reaches, after the infiltration, near-theoretical density without subsequent pressing and is widely used for Ag- and Cu-refractory contacts. For Ag/W or Ag/WC contacts, controlling the amount or excess on the bottom side of the contact of the infiltration metal Ag, results in contact tips that can be easily attached to their carriers by resistance welding. For larger Cu/W contacts, additional machining is often used to obtain the final shape of the contact component. |
− | contact manufacturing, the Infiltration process as shown on the right side of the | |
− | schematic has a broad practical range of applications. In this process the | |
− | powder of the higher melting component sometimes also as a powder mix with | |
− | a small amount of the second material is pressed into parts and after sintering | |
− | the porous skeleton is infiltrated with liquid metal of the second material. The | |
− | filling up of the pores happens through capillary forces. This process reaches
| |
− | after the infiltration near-theoretical density without subsequent pressing and is | |
− | widely used for Ag- and Cu-refractory contacts. For Ag/W or Ag/WC contacts, | |
− | controlling the amount or excess on the bottom side of the contact of the | |
− | infiltration metal Ag results in contact tips that can be easily attached to their | |
− | carriers by resistance welding. For larger Cu/W contacts additional machining is | |
− | often used to obtain the final shape of the contact component. | |
− | | |
− | ===2.2 Gold Based Materials===
| |
− | | |
− | Pure Gold is besides Platinum the chemically most stable of all precious metals.
| |
− | In its pure form it is not very suitable for use as a contact material in
| |
− | electromechanical devices because of its tendency to stick and cold-weld at even
| |
− | low contact forces. In addition it is not hard or strong enough to resist
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− | mechanical wear and exhibits high materials losses under electrical arcing
| |
− | loads. This limits its use in form of thin electroplated or vacuum deposited layers.
| |
− | | |
− | For most electrical contact applications gold alloys are used. Depending on the
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− | alloying metal the melting is performed either under in a reducing atmosphere or
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− | in a vacuum. The choice of alloying metals depends on the intended use of the
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− | resulting contact material. The binary Au alloys with typically <10 wt% of other
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− | precious metals such as Pt, Pd, or Ag or non-precious metals like Ni, Co, and
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− | Cu are the more commonly used ones (Table 2.2). On one hand these alloy
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− | additions improve the mechanical strength and electrical switching properties
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− | but on the other hand reduce the electrical conductivity and chemical corrosion
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− | resistance (Fig. 2.2) to varying degrees.
| |
− | | |
− | Under the aspect of reducing the gold content ternary alloys with a gold content
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− | of approximately 70 wt% and additions of Ag and Cu or Ag and Ni resp., for
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− | example AuAg25Cu5 or AuAg20Cu10 are used which exhibit for many
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− | applications good mechanical stability while at the same time have sufficient
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− | resistance against the formation of corrosion layers (Table 2.3). Other ternary
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− | alloys based on the AuAg system are AuAg26Ni3 and AuAg25Pt6. These alloys
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− | are mechanically similar to the AuAgCu alloys but have significantly higher
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− | oxidation resistance at elevated temperatures (Table 2.4).
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− | | |
− | Caused by higher gold prices over the past years the development of alloys with
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− | further reduced gold content had a high priority. The starting point has been the
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− | AuPd system which has continuous solubility of the two components. Besides
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− | the binary alloy of AuPd40 and the ternary one AuPd35Ag9 other multiple
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− | component alloys were developed. These alloys typically have < 50 wt% Au and
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− | often can be solution hardened in order to obtain even higher hardness and
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− | tensile strength. They are mostly used in sliding contact applications.
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− | | |
− | Gold alloys are used in the form of welded wire or profile (also called weldtapes),
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− | segments, contact rivets, and stampings produced from clad strip
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− | materials. The selection of the bonding process is based on the cost for the
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− | joining process, and most importantly on the economical aspect of using the
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− | least possible amount of the expensive precious metal component.
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− | | |
− | Besides being used as switching contacts in relays and pushbuttons, gold
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− | alloys are also applied in the design of connectors as well as sliding contacts for
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− | potentiometers, sensors, slip rings, and brushes in miniature DC motors
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− | (Table 2.5).
| |
− | | |
− | Table 2.3: Mechanical Properties of Gold and Gold-Alloys
| |
− | | |
− | Table 2.1: Commonly Used Grades of Gold
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− | | |
− | Table 2.2: Physical Properties of Gold and Gold-Alloys
| |
− | | |
− | Fig. 2.2:
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− | Influence of 1-10 atomic% of different
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− | alloying metals on the electrical resistivity of gold
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− | (according to J. O. Linde)
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− | | |
− | Fig. 2.3:
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− | Phase diagram
| |
− | of goldplatinum
| |
− | | |
− | Fig. 2.4:
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− | Phase diagram
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− | of gold-silver
| |
− | | |
− | Fig. 2.5:
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− | Phase diagram
| |
− | of gold-copper
| |
− | | |
− | Fig. 2.6: Phase diagram of gold-nickel
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− | | |
− | Fig. 2.7: Phase diagram of gold-cobalt
| |
− | | |
− | Fig. 2.8:
| |
− | Strain hardening
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− | of Au by cold working
| |
− | | |
− | Fig. 2.9:
| |
− | Softening of Au after annealing
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− | for 0.5 hrs after 80%
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− | cold working
| |
− | | |
− | Fig. 2.10:
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− | Strain hardening of
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− | AuPt10 by cold working
| |
− | | |
− | Fig. 2.11:
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− | Strain hardening
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− | of AuAg20 by cold working
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− | | |
− | Fig. 2.12:
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− | Strain hardening of
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− | AuAg30 by cold working
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− | | |
− | Fig. 2.13:
| |
− | Strain hardening of AuNi5
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− | by cold working
| |
− | | |
− | Fig. 2.14:
| |
− | Softening
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− | of AuNi5 after annealing
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− | for 0.5 hrs after 80%
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− | cold working
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− | | |
− | Fig. 2.15:
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− | Strain hardening
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− | of AuCo5 by cold working
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− | | |
− | Fig. 2.16:
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− | Precipitation hardening of
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− | AuCo5 at 400°C hardening
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− | temperature
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− | | |
− | Fig. 2.17:
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− | Strain hardening
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− | of AuAg25Pt6 by cold working
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− | | |
− | Fig. 2.18:
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− | Strain hardening
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− | of AuAg26Ni3 by cold working
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− | | |
− | Fig. 2.19:
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− | Softening
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− | of AuAg26Ni3 after
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− | annealing for 0.5 hrs
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− | after 80% cold
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− | working
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− | | |
− | Fig. 2.20:
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− | Strain hardening of
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− | AuAg25Cu5
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− | by cold working
| |
− | | |
− | Fig. 2.21:
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− | Strain hardening of
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− | AuAg20Cu10
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− | by cold working
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− | | |
− | Fig. 2.22:
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− | Softening
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− | of AuAg20Cu10 after
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− | annealing for 0.5 hrs
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− | after 80% cold working
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− | | |
− | Fig. 2.23:
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− | Strain hardening of
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− | AuCu14Pt9Ag4
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− | by cold working
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− | | |
− | Fig. 2.24:
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− | Precipitation
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− | hardening of
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− | AuCu14Pt9Ag4
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− | at different
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− | hardening
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− | temperatures
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− | after 50%
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− | cold working
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− | | |
− | Table 2.4: Contact and Switching Properties of Gold and Gold Alloys
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− | | |
− | Table 2.5: Application Examples and Forms of Gold and Gold Alloys
| |
− | | |
− | ===2.3 Platinum Metal Based Materials===
| |
− | | |
− | The platinum group metals include the elements Pt, Pd, Rh, Ru, Ir, and Os (Table
| |
− | 2.6). For electrical contacts platinum and palladium have practical significance
| |
− | as base alloy materials and ruthenium and iridium are used as alloying components.
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− | Pt and Pd have similar corrosion resistance as gold but because of their
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− | catalytical properties they tend to polymerize adsorbed organic vapors on contact
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− | surfaces. During frictional movement between contact surfaces the polymerized
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− | compounds known as “brown powder” are formed which can lead to significantly
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− | increase in contact resistance. Therefore Pt and Pd are typically used as alloys and
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− | not in their pure form for electrical contact applications.
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− | | |
− | Rhodium is not used as a solid contact material but is applied for example as a
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− | electroplated layer in sliding contact systems. Ruthenium is mostly used as an alloying
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− | component in the material PdRu15. The metals osmium and iridium have no practical
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− | applications in electrical contacts.
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− | | |
− | Since Pd was for the longest time rather stable in price it was looked at as a substitute
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− | for the more expensive gold. This was followed by a steep increase in the Pd price
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− | which caused a significant reduction in its use in electrical contacts. Today (2011) the
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− | Pd price again is lower than that of gold.
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− | | |
− | Alloys of Pt with Ru, Ir, Ni, and W were widely used in electromechanical components
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− | in the telecommunication industry and in heavy duty automotive breaker points (Table
| |
− | 2.7). Today these components have been replaced in many applications by solid
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− | state technology and the usage of these materials is greatly reduced. Pd alloys
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− | however have a more significant importance. PdCu15 is widely used for example in
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− | automotive flasher relays. Because of their resistance to sulfide formation PdAg alloys
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− | are applied in various relay designs. The ability to thermally precipitation harden some
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− | multi component alloys based on PdAgAuPt they find special usage in wear resistant
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− | sliding contact applications. Pd44Ag38Cu15PtAuZn is a standard alloy in this group.
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− | | |
− | Platinum and palladium alloys are mainly used similar to the gold based materials in
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− | the form of welded wire and profile segments but rarely as contact rivets. Because of
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− | the high precious metal prices joining technologies are used that allow the most
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− | economic application of the contact alloy in the area where functionally needed.
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− | Because of their resistance to material transfer they are used for DC applications and
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− | due to their higher arc erosion resistance they are applied for medium electrical loads
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− | up to about 30W in relays and switches (Table 2.10). Multi-component alloys based
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− | on Pd with higher hardness and wear resistance are mainly used as spring arms in
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− | sliding contact systems and DC miniature motors.
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− | | |
− | Table 2.6: Properties, Production Processes, and Application Forms for Platinum Metals
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− | | |
− | Table 2.7: Physical Properties of the Platinum Metals and their Alloys
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− | | |
− | Table 2.8: Mechanical Properties of the Platinum Metals and their Alloys
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− | | |
− | Fig. 2.25:
| |
− | Influence of 1-
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− | 20 atom% of
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− | different additive
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− | metals on the
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− | electrical
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− | resistivity p of
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− | platinum
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− | (Degussa)
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− | | |
− | Fig. 2.26:
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− | Influence of 1-22 atom% of different
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− | additive metals on the electrical
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− | resistivity
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− | p of palladium
| |
− | | |
− | Fig. 2.27:
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− | Phase diagram of
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− | platinum-iridium
| |
− | | |
− | Fig. 2.28:
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− | Phase diagram of
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− | platinum-nickel
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− | | |
− | Fig. 2.29:
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− | Phase diagram
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− | of platinum-tungsten
| |
− | | |
− | Fig. 2.30:
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− | Phase diagram of
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− | palladium-copper
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− | | |
− | Fig. 2.31:
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− | Strain
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− | hardening
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− | of Pt by cold
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− | working
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− | | |
− | Fig. 2.32:
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− | Softening of Pt after
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− | annealing for 0.5 hrs
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− | after 80%
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− | cold working
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− | | |
− | Fig. 2.33:
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− | Strain hardening of PtIr5
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− | by cold working
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− | | |
− | Fig. 2.34:
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− | Softening of PtIr5 after annealing for 1 hr
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− | after different degrees of cold working
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− | | |
− | Fig. 2.35:
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− | Strain hardening
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− | of PtNi8 by cold working
| |
− | | |
− | Fig. 2.36:
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− | Softening of PtNi8 after
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− | annealing
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− | for 1 hr after
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− | 80% cold working
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− | | |
− | Fig. 2.37:
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− | Strain hardening
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− | of PtW5 by cold working
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− | | |
− | Fig. 2.38:
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− | Softening
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− | of PtW5 after
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− | annealing for 1hr
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− | after 80% cold
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− | working
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− | | |
− | Fig. 2.39:
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− | Strain hardening
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− | of Pd 99.99 by cold working
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− | | |
− | Fig. 2.40:
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− | Strain hardening
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− | of PdCu15 by cold working
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− | | |
− | Fig. 2.41:
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− | Softening
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− | of PdCu15 after
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− | annealing
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− | for 0.5 hrs
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− | | |
− | Fig. 2.42:
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− | Strain hardening
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− | of PdCu40 by cold working
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− | | |
− | Fig. 2.43:
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− | Softening
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− | of PdCu40
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− | after annealing
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− | for 0.5 hrs after 80%
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− | cold working
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− | | |
− | Fig. 2.44:
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− | Electrical resistivity p
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− | of PdCu alloys with and without an
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− | annealing step for forming an ordered
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− | phase
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− | | |
− | Table 2.9: Contact and Switching Properties
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− | of the Platinum Metals and their Alloys
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− | | |
− | Table 2.10: Application Examples and Form
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− | of Supply for Platinum Metals and their Alloys
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− | | |
− | ===2.4 Silver Based Materials===
| |
− | | |
− | ===2.4.1 Pure Silver===
| |
− | Pure silver (also called fine silver) exhibits the highest electrical and thermal
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− | conductivity of all metals. It is also resistant against oxidation. Major disadvantages
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− | are its low mechanical wear resistance, the low softening temperature,
| |
− | and especially its strong affinity to sulfur and sulfur compounds. In the presence
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− | of sulfur and sulfur containing compounds brownish to black silver sulfide layer
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− | are formed on its surface. These can cause increased contact resistance or
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− | even total failure of a switching device if they are not mechanically, electrically,
| |
− | or thermally destroyed. Other weaknesses of silver contacts are the tendency to
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− | weld under the influence of over-currents and the low resistance against
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− | material transfer when switching DC loads. In humid environments and under
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− | the influence of an electrical field silver can creep (silver migration) and cause
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− | electrical shorting between adjacent current paths.
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− | | |
− | Table 2.11 shows the typically available quality grades of silver. In certain
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− | economic areas, i.e. China, there are additional grades with varying amounts of
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− | impurities available on the market. In powder form silver is used for a wide
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− | variety of silver based composite contact materials. Different manufacturing
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− | processes result in different grades of Ag powder as shown in Table 2.12.
| |
− | additional properties of silver powders and their usage are described
| |
− | in chapter 8.1.
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− | Semi-finished silver materials can easily be warm or cold formed and can be
| |
− | clad to the usual base materials. For attachment of silver to contact carrier
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− | materials welding of wire or profile cut-offs and brazing are most widely applied.
| |
− | Besides these mechanical processes such as wire insertion (wire staking) and
| |
− | the riveting (staking) of solid or composite contact rivets are used in the
| |
− | manufacture of contact components.
| |
− | | |
− | Contacts made from fine silver are applied in various electrical switching
| |
− | devices such as relays, pushbuttons, appliance and control switches for
| |
− | currents < 2 A (Table 2.16). Electroplated silver coatings are widely used to
| |
− | reduce the contact resistance and improve the brazing behavior of other contact
| |
− | materials and components.
| |
− | | |
− | Table 2.11: Overview of the Most Widely Used Silver Grades
| |
− | | |
− | Table 2.12: Quality Criteria of Differently Manufactured Silver Powders
| |
− | | |
− | Fig. 2.45:
| |
− | Strain hardening
| |
− | of Ag 99.95 by cold working
| |
− | | |
− | Fig. 2.46:
| |
− | Softening of Ag 99.95
| |
− | after annealing for 1 hr after different
| |
− | degrees of strain hardening
| |
− | | |
− | ===2.4.2 Silver Alloys===
| |
− | To improve the physical and contact properties of fine silver melt-metallurgical
| |
− | produced silver alloys are used (Table 2.13). By adding metal components the
| |
− | mechanical properties such as hardness and tensile strength as well as typical
| |
− | contact properties such as erosion resistance, and resistance against material
| |
− | transfer in DC circuits are increased (Table 2.14). On the other hand however,
| |
− | other properties such as electrical conductivity and chemical corrosion
| |
− | resistance can be negatively impacted by alloying (Figs. 2.47 and 2.48).
| |
− | | |
− | ===2.4.2.1 Fine-Grain Silver===
| |
− | Fine-Grain Silver (ARGODUR-Spezial) is defined as a silver alloy with an addition
| |
− | of 0.15 wt% of Nickel. Silver and nickel are not soluble in each other in solid
| |
− | form. In liquid silver only a small amount of nickel is soluble as the phase diagram
| |
− | (Fig. 2.51) illustrates. During solidification of the melt this nickel addition gets
| |
− | finely dispersed in the silver matrix and eliminates the pronounce coarse grain
| |
− | growth after prolonged influence of elevated temperatures (Figs. 2.49 and 2.50.
| |
− | | |
− | Fine-grain silver has almost the same chemical corrosion resistance as fine
| |
− | silver. Compared to pure silver it exhibits a slightly increased hardness and
| |
− | tensile strength (Table 2.14). The electrical conductivity is just slightly decreased
| |
− | by this low nickel addition. Because of its significantly improved contact
| |
− | properties fine grain silver has replaced pure silver in many applications.
| |
− | | |
− | ===2.4.2.2 Hard-Silver Alloys===
| |
− | Using copper as an alloying component increases the mechanical stability of
| |
− | silver significantly. The most important among the binary AgCu alloys is that of
| |
− | AgCu3, known in europe also under the name of hard-silver. This material still
| |
− | has a chemical corrosion resistance close to that of fine silver. In comparison to
| |
− | pure silver and fine-grain silver AgCu3 exhibits increased mechanical strength
| |
− | as well as higher arc erosion resistance and mechanical wear resistance
| |
− | (Table 2.14).
| |
− | | |
− | Increasing the Cu content further also increases the mechanical strength of
| |
− | AgCu alloys and improves arc erosion resistance and resistance against
| |
− | material transfer while at the same time however the tendency to oxide formation
| |
− | becomes detrimental. This causes during switching under arcing conditions an
| |
− | increase in contact resistance with rising numbers of operation. In special
| |
− | applications where highest mechanical strength is recommended and a reduced
| |
− | chemical resistance can be tolerated, the eutectic AgCu alloy with 28 wt% of
| |
− | copper (Fig. 2.52) is used. AgCu10 also known as coin silver has been
| |
− | replaced in many applications by composite silver-based materials while sterling
| |
− | silver (AgCu7.5) has never extended its important usage from decorative table
| |
− | wear and jewelry to industrial applications in electrical contacts.
| |
− | | |
− | Besides these binary alloys, ternary AgCuNi alloys are used in electrical contact
| |
− | applications. From this group the material ARGODUR 27, an alloy of 98 wt% Ag
| |
− | with a 2 wt% Cu and nickel addition has found practical importance close to that
| |
− | of AgCu3. This material is characterized by high resistance to oxidation and low
| |
− | tendency to re-crystallization during exposure to high temperatures. Besides
| |
− | high mechanical stability this AgCuNi alloy also exhibits a strong resistance
| |
− | against arc erosion. Because of its high resistance against material transfer the
| |
− | alloy AgCu24.5Ni0.5 has been used in the automotive industry for an extended
| |
− | time in the North American market. Caused by miniaturization and the related
| |
− | reduction in available contact forces in relays and switches this material has
| |
− | been replaced widely because of its tendency to oxide formation.
| |
− | | |
− | The attachment methods used for the hard silver materials are mostly close to
| |
− | those applied for fine silver and fine grain silver.
| |
− | | |
− | Hard-silver alloys are widely used for switching applications in the information
| |
− | and energy technology for currents up to 10 A, in special cases also for higher
| |
− | current ranges (Table 2.16).
| |
− | | |
− | Dispersion hardened alloys of silver with 0.5 wt% MgO and NiO (ARGODUR 32)
| |
− | are produced by internal oxidation. While the melt-metallurgical alloy is easy to
| |
− | cold-work and form the material becomes very hard and brittle after dispersion
| |
− | hardening. Compared to fine silver and hard-silver this material has a greatly
| |
− | improved temperature stability and can be exposed to brazing temperatures up
| |
− | to 800°C without decreasing its hardness and tensile strength.
| |
− | Because of these mechanical properties and its high electrical conductivity
| |
− | | |
− | Table 2.13: Physical Properties of Silver and Silver Alloys
| |
− | | |
− | ARGODUR 32 is mainly used in the form of contact springs that are exposed to
| |
− | high thermal and mechanical stresses in relays, and contactors for aeronautic
| |
− | applications.
| |
− | | |
− | Fig. 2.47:
| |
− | Influence of 1-10 atom% of different
| |
− | alloying metals on the electrical resistivity of
| |
− | silver
| |
− | | |
− | Fig. 2.48:
| |
− | Electrical resistivity p
| |
− | of AgCu alloys with 0-20 weight% Cu
| |
− | in the soft annealed
| |
− | and tempered stage
| |
− | a) Annealed and quenched
| |
− | b) Tempered at 280°C
| |
− | | |
− | Fig. 2.49: Coarse grain micro structure
| |
− | of Ag 99.97 after 80% cold working
| |
− | and 1 hr annealing at 600°C
| |
− | | |
− | Fig. 2.50: Fine grain microstructure
| |
− | of AgNi0.15 after 80% cold working
| |
− | and 1 hr annealing at 600°C
| |
− | | |
− | Fig. 2.51:
| |
− | Phase diagram
| |
− | of silver-nickel
| |
− | | |
− | Fig. 2.52:
| |
− | Phase diagram
| |
− | of silver-copper
| |
− | | |
− | Fig. 2.53:
| |
− | Phase diagram of
| |
− | silver-cadmium
| |
− | | |
− | Table 2.14: Mechanical Properties of Silver and Silver Alloys
| |
− | | |
− | Fig. 2.54:
| |
− | Strain hardening
| |
− | of AgCu3
| |
− | by cold working
| |
| | | |
− | Fig. 2.55:
| + | ==Gold Based Materials== |
− | Softening of AgCu3
| |
− | after annealing for 1 hr
| |
− | after 80% cold working
| |
| | | |
− | Fig. 2.56:
| + | Pure Gold is besides Platinum the chemically most stable of all precious metals. In its pure form, it is not very suitable for use as a contact material in electromechanical devices because of its tendency to stick and cold-weld at even low contact forces. In addition, it is not hard or strong enough to resist mechanical wear and exhibits high material losses under electrical arcing loads. This limits its use in form of thin electroplated or vacuum deposited layers. |
− | Strain hardening of AgCu5 by cold
| |
− | working
| |
| | | |
− | Fig. 2.57:
| + | Main Article: [[Gold Based Materials| Gold Based Materials]] |
− | Softening of AgCu5 after
| |
− | annealing for 1 hr after 80% cold
| |
− | working
| |
| | | |
− | Fig. 2.58:
| + | ==Platinum Metal Based Materials== |
− | Strain hardening of AgCu 10
| |
− | by cold working
| |
| | | |
− | Fig. 2.59:
| + | The platinum group metals include the elements Pt, Pd, Rh, Ru, Ir and Os ([[Platinum_Metal_Based_Materials|Table 1]]<!--(Table 2.6)-->). For electrical contacts, platinum and palladium have practical significance as base alloy materials and ruthenium and iridium are used as alloying components. Pt and Pd have similar corrosion resistance as gold but due to their catalytical properties, they tend to polymerize adsorbed organic vapors on contact surfaces. During frictional movement between contact surfaces, the polymerized compounds known as “brown powder” are formed, which can lead to a significant increase in contact resistance. Therefore Pt and Pd are typically used as alloys and are rather not used in their pure form for electrical contact applications. |
− | Softening of AgCu10 after
| |
− | annealing for 1 hr after 80% cold
| |
− | working
| |
| | | |
− | Fig. 2.60:
| + | Main Article: [[Platinum Metal Based Materials| Platinum Metal Based Materials]] |
− | Strain hardening of AgCu28 by
| |
− | cold working
| |
| | | |
− | Fig. 2.61:
| + | ==Silver Based Materials== |
− | Softening of AgCu28
| |
− | after annealing for 1 hr after
| |
− | 80% cold working
| |
| | | |
− | Fig. 2.62:
| + | Main Article: [[Silver Based Materials| Silver Based Materials]] |
− | Strain hardening of AgNi0.15
| |
− | by cold working
| |
| | | |
− | Fig. 2.63:
| + | ==Tungsten and Molybdenum Based Materials== |
− | Softening of AgNi0.15
| |
− | after annealing for 1 hr after 80%
| |
− | cold working
| |
| | | |
− | Fig. 2.64:
| + | Main Article: [[Tungsten and Molybdenum Based Materials| Tungsten and Molybdenum Based Materials]] |
− | Strain hardening of
| |
− | ARGODUR 27
| |
− | by cold working
| |
| | | |
− | Fig. 2.65:
| + | ==Contact Materials for Vacuum Switches== |
− | Softening
| |
− | of ARGODUR 27 after annealing
| |
− | for 1 hr after 80% cold working | |
| | | |
− | Table 2.15: Contact and Switching Properties of Silver and Silver Alloys
| + | The low gas content contact materials are developed for the use in vacuum switching devices. |
| | | |
− | Table 2.16: Application Examples and Forms of Supply for Silver and Silver Alloys
| + | Main Article: [[Contact Materials for Vacuum Switches| Contact Materials for Vacuum Switches]] |
| | | |
− | ===2.4.2.3 Silver-Palladium Alloys=== | + | ==References== |
− | The addition of 30 wt% Pd increases the mechanical properties as well as the
| |
− | resistance of silver against the influence of sulfur and sulfur containing
| |
− | compounds significantly (Tables 2.17 and 2.18).
| |
− | Alloys with 40-60 wt% Pd have an even higher resistance against silver sulfide
| |
− | formation. At these percentage ranges however the catalytic properties of
| |
− | palladium can influence the contact resistance behavior negatively. The
| |
− | formability also decreases with increasing Pd contents.
| |
| | | |
− | AgPd alloys are hard, arc erosion resistant, and have a lower tendency towards
| + | Vinaricky, E.(Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen. |
− | material transfer under DC loads (Table 2.19). On the other hand the electrical
| + | Springer-Verlag, Berlin, Heidelberg etc. 2002 |
− | conductivity is decreased at higher Pd contents. The ternary alloy AgPd30Cu5
| |
− | has an even higher hardness which makes it suitable for use in sliding contact
| |
− | systems.
| |
| | | |
− | AgPd alloys are mostly used in relays for the switching of medium to higher loads
| + | Lindmayer, M.: Schaltgeräte-Grundlagen, Aufbau, Wirkungsweise. |
− | (>60V, >2A) as shown in Table 2.20. Because of the high palladium price these
| + | Springer-Verlag, Berlin, Heidelberg, New York, Tokio, 1987 |
− | formerly solid contacts have been widely replaced by multi-layer designs such
| |
− | as AgNi0.15 or AgNi10 with a thin Au surface layer. A broader field of application
| |
− | for AgPd alloys remains in the wear resistant sliding contact systems.
| |
| | | |
− | Fig. 2.66: Phase diagram of silver-palladium
| + | Rau, G.: Metallische Verbundwerkstoffe. Werkstofftechnische |
| + | Verlagsgesellschaft, Karlsruhe 1977 |
| | | |
− | Fig. 2.67:
| + | Schreiner, H.: Pulvermetallurgie elektrischer Kontakte. Springer-Verlag |
− | Strain hardening
| + | Berlin, Göttingen, Heidelberg, 1964 |
− | of AgPd30 by cold working
| |
| | | |
− | Fig. 2.68:
| + | Hansen. M.; Anderko, K.: Constitution of Binary Alloys. New York: |
− | Strain hardening
| + | Mc Graw-Hill, 1958 |
− | of AgPd50 by cold working
| |
| | | |
− | Fig. 2.69:
| + | Shunk, F.A.: Constitution of Binary Alloy. 2 Suppl. New York; Mc Graw-Hill, 1969 |
− | Strain hardening
| |
− | of AgPd30Cu5 | |
− | by cold working
| |
| | | |
− | Fig. 2.70:
| + | Edelmetall-Taschenbuch. ( Herausgeber Degussa AG, Frankfurt a. M.), |
− | Softening of AgPd30, AgPd50,
| + | Heidelberg, Hüthig-Verlag, 1995 |
− | and AgPd30Cu5 after annealing of 1 hr
| |
− | after 80% cold working
| |
| | | |
− | Table 2.17: Physical Properties of Silver-Palladium Alloys
| + | Rau, G.: Elektrische Kontakte-Werkstoffe und Technologie. Eigenverlag G. Rau |
| + | GmbH & Co., Pforzheim, 1984 |
| | | |
− | Table 2.18: Mechanical Properties of Silver-Palladium Alloys
| + | Heraeus, W. C.: Werkstoffdaten. Eigenverlag W.C. Heraeus, Hanau, 1978 |
| | | |
− | Table 2.19: Contact and Switching Properties of Silver-Palladium Alloys
| + | Linde, J.O.: Elektrische Widerstandseigenschaften der verdünnten Legierungen |
| + | des Kupfers, Silbers und Goldes. Lund: Hakan Ohlsson, 1938 |
| | | |
− | Table 2.20: Application Examples and Forms of Suppl for Silver-Palladium Alloys
| + | Engineers Relay Handbook, RSIA, 2006 |
| | | |
− | ===2.4.3 Silver Composite Materials===
| + | Großmann, H. Saeger, K. E.; Vinaricky, E.: Gold and Gold Alloys in Electrical |
| + | Engineering. in: Gold, Progress in Chemistry, Biochemistry and Technology. John |
| + | Wiley & Sons, Chichester etc, (1999) 199-236 |
| | | |
− | ===2.4.3.1 Silver-Nickel (SINIDUR) Materials===
| + | Gehlert, B.: Edelmetall-Legierungen für elektrische Kontakte. |
− | Since silver and nickel are not soluble in each other in solid form and in the liquid
| + | Metall 61 (2007) H. 6, 374-379 |
− | phase have only very limited solubility silver nickel composite materials with
| |
− | higher Ni contents can only be produced by powder metallurgy. During extrusion
| |
− | of sintered Ag/Ni billets into wires, strips and rods the Ni particles embedded in
| |
− | the Ag matrix are stretched and oriented in the microstructure into a pronounced
| |
− | fiber structure (Figs. 2.75. and 2.76)
| |
| | | |
− | The high density produced during hot extrusion aids the arc erosion resistance
| + | Aldinger, F.; Schnabl, R.: Edelmetallarme Kontakte für kleine Ströme. |
− | of these materials (Tables 2.21 and 2.22). The typical application of Ag/Ni
| + | Metall 37 (1983) 23-29 |
− | contact materials is in devices for switching currents of up to 100A (Table 2.24).
| |
− | In this range they are significantly more erosion resistant than silver or silver
| |
− | alloys. In addition they exhibit with nickel contents <20 wt% a low and over their
| |
− | operational lifetime consistent contact resistance and good arc moving
| |
− | properties. In DC applications Ag/Ni materials exhibit a relatively low tendency
| |
− | of material transfer distributed evenly over the contact surfaces (Table 2.23).
| |
| | | |
− | Typically Ag/Ni (SINIDUR) materials are usually produced with contents of 10-40
| + | Bischoff, A.; Aldinger, F.: Einfluss geringer Zusätze auf die mechanischen |
− | wt% Ni. The most widely used materials SINIDUR 10 and SINIDUR 20- and also
| + | Eigenschaften von Au-Ag-Pd-Legierungen. Metall 36 (1982) 752-765 |
− | SINIDUR 15, mostly used in north america-, are easily formable and applied by
| |
− | cladding (Figs. 2.71-2.74). They can be, without any additional welding aids,
| |
− | economically welded and brazed to the commonly used contact carrier
| |
− | materials.
| |
− | The (SINIDUR) materials with nickel contents of 30 and 40 wt% are used in
| |
− | switching devices requiring a higher arc erosion resistance and where increases
| |
− | in contact resistance can be compensated through higher contact forces.
| |
| | | |
− | The most important applications for Ag/Ni contact materials are typically in
| + | Wise, E.M.: Palladium, Recovery, Properties and Uses. New York, London: |
− | relays, wiring devices, appliance switches, thermostatic controls, auxiliary
| + | Academic Press 1968 |
− | switches, and small contactors with nominal currents >20A (Table 2.24).
| |
| | | |
− | Table 2.21: Physical Properties of Silver-Nickel (SINIDUR) Materials
| + | Savitskii, E.M.; Polyakova, V.P.; Tylina, M.A.: Palladium Alloys, Primary Sources. |
| + | New York: Publishers 1969 |
| | | |
− | Table 2.22: Mechanical Properties of Silver-Nickel (SINIDUR) Materials
| + | Gehlert, B.: Lebensdaueruntersuchungen von Edelmetall Kontaktwerkstoff- |
| + | Kombinationen für Schleifringübertrager. VDE-Fachbericht 61, (2005) 95-100 |
| | | |
− | Fig. 2.71:
| + | Holzapfel,C.: Verschweiß und elektrische Eigenschaften von |
− | Strain hardening
| + | Schleifringübertragern. VDE-Fachbericht 67 (2011) 111-120 |
− | of Ag/Ni 90/10 by cold working
| |
| | | |
− | Fig. 2.72:
| + | Schnabl, R.; Gehlert, B.: Lebensdauerprüfungen von Edelmetall- |
− | Softening of Ag/Ni 90/10
| + | Schleifkontaktwerkstoffen für Gleichstrom Kleinmotoren. |
− | after annealing
| + | Feinwerktechnik & Messtechnik (1984) 8, 389-393 |
− | for 1 hr after 80% cold working
| |
| | | |
− | Fig. 2.73:
| + | Kobayashi, T.; Koibuchi, K.; Sawa, K.; Endo, K.; Hagino, H.: A Study of Lifetime |
− | Strain hardening
| + | of Au-plated Slip-Ring and AgPd Brush System for Power Supply. |
− | of Ag/Ni 80/20 by cold working
| + | th Proc. 24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 537-542 |
| | | |
− | Fig. 2.74:
| + | Harmsen, U.; Saeger K.E.: Über das Entfestigungsverhalten von Silber |
− | Softening of Ag/Ni 80/20
| + | verschiedener Reinheiten. Metall 28 (1974) 683-686 |
− | after annealing
| |
− | for 1 hr after 80% cold working
| |
| | | |
− | Fig. 2.75: Micro structure of Ag/Ni 90/10 a) perpendicular to the extrusion direction
| + | Behrens, V.; Michal, R.; Minkenberg, J.N.; Saeger, K.E.: Abbrand und |
− | b) parallel to the extrusion direction
| + | Kontaktwiderstandsverhalten von Kontaktwerkstoffen auf Basis von Silber- |
| + | Nickel. e.& i. 107. Jg. (1990), 2, 72-77 |
| | | |
− | Fig. 2.76: Micro structure of Ag/Ni 80/20 a) perpendicular to the extrusion direction
| + | Behrens, V.: Silber/Nickel und Silber/Grafit- zwei Spezialisten auf dem Gebiet |
− | b) parallel t o the extrusion direction
| + | der Kontaktwerkstoffe. Metall 61 (2007) H.6, 380-384 |
| | | |
− | Table 2.23: Contact and Switching Properties of Silver-Nickel (SINIDUR) Materials
| + | Rieder, W.: Silber / Metalloxyd-Werkstoffe für elektrische Kontakte, |
| + | VDE - Fachbericht 42 (1991) 65-81 |
| | | |
− | Table 2.24: Application Examples and Forms of Supply
| + | Harmsen,U.: Die innere Oxidation von AgCd-Legierungen unter |
− | for Silver-Nickel (SINIDUR) Materials
| + | Sauerstoffdruck. |
| + | Metall 25 (1991), H.2, 133-137 |
| | | |
− | ===2.4.3.2: Silver-Metal Oxide Materials Ag/CdO, Ag/SnO , Ag/ZnO===
| + | Muravjeva, E.M.; Povoloskaja, M.D.: Verbundwerkstoffe Silber-Zinkoxid und |
− | The family of silver-metal oxide contact materials includes the material groups:
| + | Silber-Zinnoxid, hergestellt durch Oxidationsglühen. |
− | silver-cadmium oxide (DODURIT CdO), silver-tin oxide (SISTADOX), and silverzinc
| + | Elektrotechnika 3 (1965) 37-39 |
− | oxide (DODURIT ZnO). Because of their very good contact and switching
| |
− | properties like high resistance against welding, low contact resistance, and high
| |
− | arc erosion resistance, silver-metal oxides have gained an outstanding position
| |
− | in a broad field of applications. They mainly are used in low voltage electrical
| |
− | switching devices like relays, installation and distribution switches, appliances,
| |
− | industrial controls, motor controls, and protective devices (Table 2.13).
| |
| | | |
− | *Silver-cadmium oxide (DODURIT CdO) materials
| + | Behrens, V.; Honig Th.; Kraus, A.; Michal, R.; Saeger, K.-E.; Schmidberger, R.; |
| + | Staneff, Th.: Eine neue Generation von AgSnO<sub>2</sub> -Kontaktwerkstoffen. |
| + | VDE-Fachbericht 44, (1993) 99-114 |
| | | |
− | Silver-cadmium oxide (DODURIT CdO) materials with 10-15 wt% are produced
| + | Braumann, P.; Lang, J.: Kontaktverhalten von Ag-Metalloxiden für den Bereich |
− | by both, internal oxidation and powder metallurgical methods (Table 2.25).
| + | hoher Ströme. VDE-Fachbericht 42, (1991) 89-94 |
| | | |
− | The manufacturing of strips and wires by internal oxidation starts with a molten
| + | Hauner, F.; Jeannot, D.; Mc Neilly, U.; Pinard, J.: Advanced AgSnO Contact 2 |
− | alloy of silver and cadmium. During a heat treatment below it's melting point in a
| + | th Materials for High Current Contactors. Proc. 20 Int. Conf. on Electr. Contact |
− | oxygen rich atmosphere in such a homogeneous alloy the oxygen diffuses from
| + | Phenom., Stockholm 2000, 193-198 |
− | the surface into the bulk of the material and oxidizes the Cd to CdO in a more or
| |
− | less fine particle precipitation inside the Ag matrix. The CdO particles are rather
| |
− | fine in the surface area and are becoming larger further away towards the center
| |
− | of the material (Fig. 2.83).
| |
| | | |
− | During the manufacturing of Ag/CdO contact material by internal oxidation the
| + | Wintz, J.-L.; Hardy, S.; Bourda, C.: Influence on the Electrical Performances of |
− | processes vary depending on the type of semi-finished material.
| + | Assembly Process, Supports Materials and Production Means for AgSnO<sub>2</sub> . |
− | For Ag/CdO wires a complete oxidation of the AgCd wire is performed, followed
| + | Proc.24<sub>th</sub> Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 75-81 |
− | by wire-drawing to the required diameter (Figs. 2.77 and 2.78). The resulting
| |
− | material is used for example in the production of contact rivets. For Ag/CdO strip
| |
− | materials two processes are commonly used: Cladding of an AgCd alloy strip
| |
− | with fine silver followed by complete oxidation results in a strip material with a
| |
− | small depletion area in the center of it's thickness and a Ag backing suitable for
| |
− | easy attachment by brazing (sometimes called “Conventional Ag/CdO”). Using
| |
− | a technology that allows the partial oxidation of a dual-strip AgCd alloy material
| |
− | in a higher pressure pure oxygen atmosphere yields a composite Ag/CdO strip
| |
− | material that has besides a relatively fine CdO precipitation also a easily brazable
| |
− | AgCd alloy backing (Fig. 2.85). These materials (DODURIT CdO ZH) are mainly
| |
− | used as the basis for contact profiles and contact tips.
| |
| | | |
− | During powder metallurgical production the powder mixed made by different
| + | Behrens, V.; Honig, Th.; Kraus, A.; Michal, R.: Schalteigenschaften von |
− | processes are typically converted by pressing, sintering and extrusion to wires
| + | verschiedenen Silber-Zinnoxidwerkstoffen in Kfz-Relais. VDE-Fachbericht 51 |
− | and strips. The high degree of deformation during hot extrusion produces a
| + | (1997) 51-57 |
− | uniform and fine dispersion of CdO particles in the Ag matrix while at the same
| |
− | time achieving a high density which is advantageous for good contact properties
| |
− | (Fig. 2.84). To obtain a backing suitable for brazing, a fine silver layer is applied
| |
− | by either com-pound extrusion or hot cladding prior to or right after the extrusion
| |
− | (Fig. 2.86). | |
| | | |
− | For larger contact tips, and especially those with a rounded shape, the single tip
| + | Schöpf, Th.: Silber/Zinnoxid und andere Silber-Metalloxidwerkstoffe in |
− | Press-Sinter-Repress process (PSR) offers economical advantages. The
| + | Netzrelais. VDE-Fachbericht 51 (1997) 41-50 |
− | powder mix is pressed in a die close to the final desired shape, the “green” tips
| |
− | are sintered, and in most cases the repress process forms the final exact shape
| |
− | while at the same time increasing the contact density and hardness.
| |
| | | |
− | Using different silver powders and minor additives for the basic Ag and CdO
| + | Schöpf, Th.; Behrens, V.; Honig, Th.; Kraus, A.: Development of Silver Zinc |
− | starting materials can help influence certain contact properties for specialized
| + | th Oxide for General-Purpose Relays. Proc. 20 Int. Conf. on Electr. Contacts, |
− | applications.
| + | Stockholm 2000, 187-192 |
| | | |
− | Fig. 2.77:
| + | Braumann, P.; Koffler, A.: Einfluss von Herstellverfahren, Metalloxidgehalt und |
− | Strain hardening of internally oxidized
| + | Wirkzusätzen auf das Schaltverhalten von Ag/SnO in Relais. 2 |
− | Ag/CdO 90/10 by cold working | + | VDE-Fachbericht 59, (2003) 133-142 |
| | | |
− | Fig. 2.78:
| + | Kempf, B.; Braumann, P.; Böhm, C.; Fischer-Bühner, J.: Silber-Zinnoxid- |
− | Softening of internally oxidized
| + | Werkstoffe: Herstellverfahren und Eigenschaften. Metall 61(2007) H. 6, 404-408 |
− | Ag/CdO 90/10 after annealing
| |
− | for 1 hr after 40% cold working
| |
| | | |
− | Table 2.25: Physical and Mechanical Properties as well as Manufacturing Processes and
| + | Lutz, O.; Behrens, V.; Finkbeiner, M.; Honig, T.; Späth, D.: Ag/CdO-Ersatz in |
− | Forms of Supply of Extruded Silver Cadmium Oxide
| + | Lichtschaltern. VDE-Fachbericht 61, (2005) 165-173 |
− | (DODURIT CdO) Contact Materials | |
| | | |
− | Fig. 2.79:
| + | Lutz, O.; Behrens, V.; Wasserbäch, W.; Franz, S.; Honig, Th.; Späth, |
− | Strain hardening of
| + | D.; Heinrich, J.: Improved Silver/Tin Oxide Contact Materials for Automotive |
− | Ag/CdO 90/10 P by cold working
| + | th Applications. Proc.24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008, |
| + | 88-93 |
| | | |
− | Fig. 2.80: Softening
| + | Leung, C.; Behrens, V.: A Review of Ag/SnO Contact Materials and Arc Erosion. 2 |
− | of Ag/CdO 90/10 P after annealing | + | th Proc.24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 82-87 |
− | for 1 hr after 40% cold working
| |
| | | |
− | Fig. 2.81:
| + | Chen, Z.K.; Witter, G.J.: Comparison in Performance for Silver–Tin–Indium |
− | Strain hardening
| + | Oxide Materials Made by Internal Oxidation and Powder Metallurgy. |
− | of Ag/CdO 88/12 WP
| + | th Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver, BC, Canada, |
| + | (2009) 167 – 176 |
| | | |
− | Fig. 2.82:
| + | Roehberg, J.; Honig, Th.; Witulski, N.; Finkbeiner, M.; Behrens, V.: Performance |
− | Softening of Ag/CdO 88/12WP after annealing
| + | of Different Silver/Tin Oxide Contact Materials for Applications in Low Voltage |
− | for 1 hr after different degrees of
| + | th Circuit Breakers. Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver, |
− | cold working
| + | BC, Canada, (2009) 187 – 194 |
| | | |
− | Fig. 2.83: Micro structure of Ag/CdO 90/10 i.o. a) close to surface
| + | Muetzel, T.; Braumann, P.; Niederreuther, R.: Temperature Rise Behavior of |
− | b) in center area
| + | th Ag/SnO Contact Materials for Contactor Applications. Proc. 55 IEEE Holm 2 |
| + | Conf. on Electrical Contacts, Vancouver, BC, Canada, (2009) 200 – 205 |
| | | |
− | Fig. 2.84: Micro structure of Ag/CdO 90/10 P:
| + | Lutz, O. et al.: Silber/Zinnoxid – Kontaktwerkstoffe auf Basis der Inneren |
− | a) perpendicular to extrusion direction
| + | Oxidation fuer AC – und DC – Anwendungen. |
− | b) parallel to extrusion direction
| + | VDE Fachbericht 65 (2009) 167 – 176 |
| | | |
− | Fig. 2.85:
| + | Harmsen, U.; Meyer, C.L.: Mechanische Eigenschaften stranggepresster Silber- |
− | Micro structure of Ag/CdO 90/10 ZH:
| + | Graphit-Verbundwerkstoffe. Metall 21 (1967), 731-733 |
− | 1) Ag/CdO layer
| |
− | 2) AgCd backing layer
| |
| | | |
− | Fig. 2.86: Micro structure of AgCdO 88/12 WP: a) perpendicular to extrusion direction
| + | Behrens, V.: Mahle, E.; Michal, R.; Saeger, K.E.: An Advanced Silver/Graphite |
− | b) parallel to extrusion direction
| + | th Contact Material Based on Graphite Fibre. Proc. 16 Int. Conf. on Electr. |
| + | Contacts, Loghborough 1992, 185-189 |
| | | |
− | *Silver–tin oxide(SISTADOX)materials
| + | Schröder, K.-H.; Schulz, E.-D.: Über den Einfluss des Herstellungsverfahrens |
− | Over the past years, many Ag/CdO contact materials have been replaced by
| + | th auf das Schaltverhalten von Kontaktwerkstoffen der Energietechnik. Proc. 7 Int. |
− | Ag/SnO<sub>2</sub> based materials with 2-14 wt% SnO<sub>2</sub> because of the toxicity of
| + | Conf. on Electr. Contacts, Paris 1974, 38-45 |
− | Cadmium. This changeover was further favored by the fact that Ag/SnO<sub>2</sub>
| |
− | contacts quite often show improved contact and switching properties such as
| |
− | lower arc erosion, higher weld resistance, and a significant lower tendency
| |
− | towards material transfer in DC switching circuits ''(Table 2.30)''. Ag/SnO<sub>2</sub>
| |
− | materials have been optimized for a broad range of applications by other metal
| |
− | oxide additives and modification in the manufacturing processes that result in
| |
− | different metallurgical, physical and electrical properties ''(Table 2.29)''.
| |
| | | |
− | Manufacturing of Ag/SnO<sub>2</sub> by ''internal oxidation'' is possible in principle, but
| + | Mützel, T.: Niederreuther, R.: Kontaktwerkstoffe für Hochleistungsanwendungen. |
− | during heat treatment of alloys containing > 5 wt% of tin in oxygen, dense oxide
| + | VDE-Bericht 67 (2011) 103-110 |
− | layers formed on the surface of the material prohibit the further diffusion of
| |
− | oxygen into the bulk of the material. By adding Indium or Bismuth to the alloy the
| |
− | internal oxidation is possible and results in materials that typically are rather hard
| |
− | and brittle and may show somewhat elevated contact resistance and is limited
| |
− | to applications in relays. To make a ductile material with fine oxide dispersion
| |
− | (SISTADOX TOS F) ''(Fig. 2.114)'' it is necessary to use special process variations | |
− | in oxidation and extrusion which lead to materials with improved properties in
| |
− | relays. Adding a brazable fine silver layer to such materials results in a semifinished
| |
− | material suitable for the manufacture as smaller weld profiles
| |
− | (SISTADOX WTOS F) ''(Fig. 2.116)''. Because of their resistance to material
| |
− | transfer and low arc erosion these materials find for example a broader
| |
− | application in automotive relays ''(Table 2.31)''.
| |
| | | |
− | ''Powder metallurgy'' plays a significant role in the manufacturing of Ag/SnO<sub>2</sub>
| + | Lambert, C.; Cambon, G.: The Influence of Manufacturing Conditions and |
− | contact materials. Besides SnO<sub>2</sub> a smaller amount (<1 wt%) of one or more
| + | Metalurgical Characteristics on the Electrical Behaviour of Silver-Graphite |
− | other metal oxides such as WO<sub>3</sub>, MoO<sub>3</sub>, CuO and/or Bi<sub>2</sub>O<sub>3</sub> are added. These
| + | th Contact Materials. Proc. 9 Int. Conf.on Electr. Contacts, |
− | additives improve the wettability of the oxide particles and increase the viscosity
| + | Chicago 1978, 401-406 |
− | of the Ag melt. They also provide additional benefits to the mechanical and
| |
− | arcing contact properties of materials in this group ''(Table 2.26)''.
| |
| | | |
− | In the manufacture the initial powder mixes different processes are applied
| + | Vinaricky, E.: Grundsätzliche Untersuchungen zum Abbrand- und |
− | which provide specific advantages of the resulting materials in respect to their
| + | Schweißverhalten von Ag/C-Kontaktwerkstoffen. VDE-Fachbericht 47 (1995) |
− | contact properties ''(Figs. 2.87 – 2.119)''. Some of them are described here as
| + | 159-169 |
− | follows:
| |
− | :'''a) Powder blending from single component powders''' <br> In this common process all components including additives that are part of the powder mix are blended as single powders. The blending is usually performed in the dry stage in blenders of different design.
| |
| | | |
− | :'''b) Powder blending on the basis of doped powders''' <br> For incorporation of additive oxides in the SnO<sub>2</sub> powder the reactive spray process (RSV) has shown advantages. This process starts with a waterbased solution of the tin and other metal compounds. This solution is nebulized under high pressure and temperature in a reactor chamber. Through the rapid evaporation of the water each small droplet is converted into a salt crystal and from there by oxidation into a tin oxide particle in which the additive metals are distributed evenly as oxides. The so created doped AgSnO2 powder is then mechanically mixed with silver powder.
| + | Agte, C.; Vacek, J.: Wolfram und Molybdän. Berlin: Akademie-Verlag 1959 |
| | | |
− | :'''c) Powder blending based on coated oxide powders''' <br> In this process tin oxide powder is blended with lower meting additive oxides such as for example Ag<sub>2</sub> MoO<sub>4</sub> and then heat treated. The SnO<sub>2</sub> particles are coated in this step with a thin layer of the additive oxide. | + | Keil, A.; Meyer, C.-L.: Der Einfluß des Faserverlaufes auf die elektrische |
| + | Verschleißfestigkeit von Wolfram-Kontakten. ETZ 72, (1951) 343-346 |
| | | |
− | :'''d) Powder blending based on internally oxidized alloy powders''' <br> A combination of powder metallurgy and internal oxidation this process starts with atomized Ag alloy powder which is subsequently oxidized in pure oxygen. During this process the Sn and other metal components are transformed to metal oxide and precipitated inside the silver matrix of each powder particle. | + | Slade, P. G.: Electric Contacts for Power Interruption. A Review. Proc. 19 Int. |
| + | Conf. on Electric Contact Phenom. Nuremberg (Germany) 1998, 239-245 |
| | | |
− | :'''e) Powder blending based on chemically precipitated compound powders''' <br> A silver salt solution is added to a suspension of for example SnO<sub>2</sub> together with a precipitation agent. In a chemical reaction silver and silver oxide respectively are precipitated around the additive metal oxide particles who act as crystallization sites. Further chemical treatment then reduces the silver oxide with the resulting precipitated powder being a mix of Ag and SnO<sub>2</sub>. | + | Slade, P. G.: Variations in Contact Resistance Resulting from Oxide Formation |
| + | and Decomposition in AgW and Ag-WC-C Contacts Passing Steady Currents |
| + | for Long Time Periods. IEEE Trans. Components, Hybrids and Manuf. Technol. |
| + | CHMT-9,1 (1986) 3-16 |
| | | |
− | Further processing of these differently produced powders follows the
| + | Slade, P. G.: Effect of the Electric Arc and the Ambient Air on the Contact |
− | conventional processes of pressing, sintering and hot extrusion to wires and
| + | Resistance of Silver, Tungsten and Silver-Tungsten Contacts. |
− | strips. From these contact parts such as contact rivets and tips are
| + | J.Appl.Phys. 47, 8 (1976) 3438-3443 |
− | manufactured. To obtain a brazable backing the same processes as used for
| |
− | Ag/CdO are applied. As for Ag/CdO, larger contact tips can also be
| |
− | manufactured more economically using the press-sinter-repress (PSR) process
| |
− | ''(Table 2.27).''
| |
| | | |
− | Fig. 2.87:
| + | Lindmayer, M.; Roth, M.: Contact Resistance and Arc-Erosion of W-Ag and |
− | Strain hardening of
| + | WC-Ag. IEEE Trans components, Hybrids and Manuf. Technol. |
− | Ag/SnO<sub>2</sub> 92/8 PE by cold working | + | CHMT-2, 1 (1979) 70-75 |
| | | |
− | Fig. 2.88:
| + | Leung, C.-H.; Kim, H.J.: A Comparison of Ag/W, Ag/WC and Ag/Mo Electrical |
− | Softening of
| + | Contacts. IEEE Trans. Components, Hybrids, Manuf. Technol., |
− | Ag/SnO<sub>2</sub> 92/8 PE after annealing | + | Vol. CHMT-7, 1 (1984) 69-75 |
− | for 1 hr after 40% cold working
| |
| | | |
− | Table 2.26: Physical and Mechanical Properties as well as Manufacturing Processes and
| + | Allen, S.E.; Streicher, E.: The Effect of Microstructure on the Electrical |
− | Forms of Supply of Extruded Silver-Tin Oxide (SISTADOX) Contact Materials
| + | th Performance of Ag-WC-C Contact Materials. Proc. 44 IEEE Holm Conf. on Electr. |
| + | Contacts, Arlington, VA, USA (1998), 276-285 |
| | | |
− | Fig. 2.89:
| + | Haufe, W.; Reichel, W.; Schreiner H.: Abbrand verschiedener W/Cu-Sinter- |
− | Strain hardening of
| + | Tränkwerkstoffe an Luft bei hohen Strömen. Z. Metallkd. 63 (1972) 651-654 |
− | Ag/SnO<sub>2</sub> 88/12 PE by cold working
| |
| | | |
− | Fig. 2.90:
| + | Althaus, B.; Vinaricky, E.: Das Abbrandverhalten verschieden hergestellter |
− | Softening of Ag/SnO<sub>2</sub> 88/12 PE
| + | Wolfram-Kupfer-Verbundwerkstoffe im Hochstromlichtbogen. |
− | after annealing for
| + | Metall 22 (1968) 697-701 |
− | 1 hr after 40% cold working
| |
| | | |
− | Fig. 2.91:
| + | Gessinger, G.H.; Melton, K.N.: Burn-off Behaviour of WCu Contact Materials in an |
− | Strain hardening of oxidized
| + | Electric Arc. Powder Metall. Int. 9 (1977) 67-72 |
− | Ag/SnO<sub>2</sub> 88/12 PW4 by cold working
| |
| | | |
− | Fig. 2.92:
| + | Magnusson, M.: Abbrandverhalten und Rißbildung bei WCu-Tränkwerkstoffen |
− | Softening of Ag/SnO<sub>2</sub> 88/12 PW4 after
| + | unterschiedlicher Wolframteilchengröße. ETZ-A 98 (1977) 681-683 |
− | annealing for 1 hr
| |
− | after 30% cold working
| |
| | | |
− | Fig. 2.93:
| + | Heitzinger, F.; Kippenberg, H.; Saeger, K.E.; Schröder, K.H.: Contact Materials for |
− | Strain hardening of
| + | Vacuum Switching Devices. Proc. XVth ISDEIV, Darmstadt 1992, 273-278 |
− | Ag/SnO<sub>2</sub> 98/2 PX
| |
− | by cold working
| |
| | | |
− | Fig. 2.94:
| + | Grill, R.; Müller, F.: Verbundwerkstoffe auf Wolframbasis für |
− | Softening of
| + | Hochspannungsschaltgeräte. Metall 61 (2007) H. 6, 390-393 |
− | Ag/SnO<sub>2</sub> 98/2 PX
| |
− | after annealing
| |
− | for 1 hr after 80%
| |
− | cold working
| |
| | | |
− | Fig 2.95:
| + | Slade, P.: G.: The Vacuum Interrupter- Theory; Design; and Application. CRC |
− | Strain hardening
| + | Press, Boca Raton, FL (USA), 2008 |
− | of Ag/SnO<sub>2</sub> 92/8 PX
| |
− | by cold working
| |
| | | |
− | Fig. 2.96:
| + | Frey, P.; Klink, N.; Saeger, K.E.: Untersuchungen zum Abreißstromverhalten von |
− | Softening of
| + | Kontaktwerkstoffen für Vakuumschütze. Metall 38 (1984) 647-651 |
− | Ag/SnO<sub>2</sub> 92/8 PX
| |
− | after annealing for 1 hr
| |
− | after 40% cold working
| |
| | | |
− | Fig. 2.97:
| + | Frey, P.; Klink, N.; Michal, R.; Saeger, K.E.: Metallurgical Aspects of Contact |
− | Strain hardening of internally
| + | Materials for Vacuum Switching Devices. IEEE Trans. Plasma Sc. 17, (1989) 743- |
− | oxidized
| + | 740 |
− | Ag/SnO<sub>2</sub> 88/12 TOS F
| |
− | by cold working
| |
| | | |
− | Fig. 2.98:
| + | Slade, P.: Advances in Material Development for High Power Vacuum Interrupter |
− | Softening of
| + | th Contacts. Proc.16 Int. Conf. on Electr. Contact Phenom., |
− | Ag/SnO<sub>2</sub> 88/12 TOS F after
| + | Loughborough 1992,1-10 |
− | annealing for 1 hr after 30%
| |
− | cold working
| |
| | | |
− | Fig. 2.99:
| + | Behrens, V.; Honig, Th.; Kraus, A.; Allen, S.: Comparison of Different Contact |
− | Strain hardening of
| + | th Materials for Low Voltage Vacuum Applications. Proc.19 Int. Conf. on Electr. |
− | internally oxidized
| + | Contact Phenom., Nuremberg 1998, 247-251 |
− | Ag/SnO<sub>2</sub> 88/12P
| |
− | by cold working
| |
| | | |
− | Fig. 2.100:
| + | Rolle, S.; Lietz, A.; Amft, D.; Hauner, F.: CuCr Contact Material for Low Voltage |
− | Softening of
| + | th Vacuum Contactors. Proc. 20 int. Conf. on Electr. Contact. Phenom. Stockholm |
− | Ag/SnO<sub>2</sub> 88/12P
| + | 2000, 179-186 |
− | after annealing for 1 hr after
| |
− | 40% cold working
| |
| | | |
− | Fig. 2.101:
| + | Kippenberg, H.: CrCu as a Contact Material for Vacuum Interrupters. |
− | Strain hardening of
| + | th Proc.13 Int. Conf. on Electr. Contact Phenom. Lausanne 1986, 140-144 |
− | Ag/SnO<sub>2</sub> 88/12 WPC
| |
− | by cold working
| |
| | | |
− | Fig. 2.102:
| + | Hauner, F.; Müller, R.; Tiefel, R.: CuCr für Vakuumschaltgeräte- |
− | Softening of Ag/SnO<sub>2</sub> 88/12 WPC after annealing
| + | Herstellungsverfahren, Eigenschaften und Anwendung. |
− | for 1 hr after different degrees of cold working
| + | Metall 61 (2007) H. 6, 385-389 |
| | | |
− | Fig. 2.103:
| + | Manufacturing Equipment for Semi-Finished Materials |
− | Strain hardening of
| |
− | Ag/SnO<sub>2</sub> 86/14 WPC
| |
− | by cold working
| |
− | | |
− | Fig. 2.104:
| |
− | Softening of Ag/SnO<sub>2</sub> 86/14 WPC after annealing
| |
− | for 1 hr after different degrees of cold working
| |
− | | |
− | Fig. 2.105:
| |
− | Strain hardening of
| |
− | Ag/SnO<sub>2</sub> 88/12 WPD
| |
− | by cold working
| |
− | | |
− | Fig. 2.106:
| |
− | Softening of Ag/SnO<sub>2</sub> 88/12 WPD after
| |
− | annealing for 1 hr after different degrees
| |
− | of cold working
| |
− | | |
− | Fig. 2.108:
| |
− | Softening of Ag/SnO<sub>2</sub> 88/12 WPX after
| |
− | annealing for 1 hr after different degrees
| |
− | of cold working
| |
− | | |
− | Fig. 2.107:
| |
− | Strain hardening of
| |
− | Ag/SnO<sub>2</sub> 88/12 WPX
| |
− | by cold working
| |
− | | |
− | Fig. 2.109: Micro structure of Ag/SnO<sub>2</sub> 92/8 PE: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction
| |
− | | |
− | Fig. 2.110: Micro structure of Ag/SnO<sub>2</sub> 88/12 PE: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction
| |
− | | |
− | Fig. 2.111: Micro structure of Ag/SnO<sub>2</sub> 88/12 PW: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction
| |
− | | |
− | Fig. 2.112: Micro structure of Ag/SnO<sub>2</sub> 98/2 PX: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction
| |
− | | |
− | Fig. 2.113: Micro structure of Ag/SnO<sub>2</sub> 92/8 PX: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction
| |
− | | |
− | Fig. 2.114: Micro structure of Ag/SnO<sub>2</sub> 88/12 TOS F: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction
| |
− | | |
− | Fig. 2.115: Micro structure of Ag/SnO<sub>2</sub> 86/14 WPC: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction, 1) AgSnO<sub>2</sub> contact layer, 2) Ag backing layer
| |
− | | |
− | Fig. 2.116: Micro structure of Ag/SnO<sub>2</sub> 92/8 WTOS F: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction,1) AgSnO<sub>2</sub> contact layer, 2) Ag backing layer
| |
− | | |
− | Fig. 2.117: Micro structure of
| |
− | Ag/SnO<sub>2</sub> 88/12 WPD: parallel to extrusion direction
| |
− | 1) AgSnO<sub>2</sub> contact layer, 2) Ag backing layer
| |
− | | |
− | Fig. 2.118: Micro structure of
| |
− | Ag/SnO<sub>2</sub> 88/12 WPX:parallel to extrusion direction
| |
− | 1) AgSnO<sub>2</sub> contact layer, 2) Ag backing layer
| |
− | | |
− | Fig. 2.119: Micro structure of Ag/SnO<sub>2</sub> 86/14 WPX: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction, 1) AgSnO<sub>2</sub> contact layer, 2) Ag backing layer
| |
− | | |
− | Table 2.27: Physical Properties of Powder Metallurgical Silver-Metal Oxide Materials
| |
− | with Fine Silver Backing Produced by the Press-Sinter-Repress Process
| |
− | | |
− | *'''Silver–zinc oxide (DODURIT ZnO) materials'''
| |
− | Silver zinc oxide (DODURIT ZnO) contact materials with mostly 6 - 10 wt% oxide
| |
− | content including other small metal oxides are produced exclusively by powder
| |
− | metallurgy ''(Figs. 2.120 – 2.125)'' ''(Table 2.28)''. Adding Ag<sub>2</sub>WO<sub>4</sub> in the process b)
| |
− | as described in the preceding chapter on Ag/SnO<sub>2</sub> has proven most effective
| |
− | for applications in AC relays, wiring devices, and appliance controls. Just like
| |
− | with the other Ag metal oxide materials, semi-finished materials in strip and wire
| |
− | form are used to manufacture contact tips and rivets.
| |
− | Because of their high resistance against welding and arc erosion Ag/ZnO
| |
− | materials present an economic alternative to Cd free Ag-tin oxide contact
| |
− | materials ''(Tables 2.30 and 2.31)''.
| |
− | | |
− | Table 2.28: Physical and Mechanical Properties as well as Manufacturing Processes and
| |
− | Forms of Supply of Extruded Silver-Zinc Oxide (DODURIT ZnO) Contact
| |
− | | |
− | Fig. 2.120: Strain hardening of
| |
− | Ag/ZnO 92/8 PW25 by cold working
| |
− | | |
− | Fig. 2.121: Softening of Ag/ZnO 92/8 PW25
| |
− | after annealing for 1 hr after 30% cold working
| |
− | | |
− | Fig. 2.122: Strain hardening of
| |
− | Ag/ZnO 92/8 WPW25
| |
− | by cold working
| |
− | | |
− | Fig. 2.123: Softening of
| |
− | Ag/ZnO 92/8 WPW25 after annealing for
| |
− | 1hr after different degrees of cold working
| |
− | | |
− | Fig. 2.115: Micro structure of Ag/ZnO 92/8 Pw25: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction
| |
− | | |
− | Fig. 2.116: Micro structure of Ag/ZnO 92/8 WPW25:a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction, 1) Ag/ZnO contact layer, 2) Ag backing layer
| |
− | | |
− | Table 2.29: Optimizing of Silver–Tin Oxide Materials Regarding their Switching
| |
− | Properties and Forming Behavior
| |
− | | |
− | Table 2.30: Contact and Switching Properties of Silver–Metal Oxide Materials
| |
− | | |
− | Table 2.31: Application Examples of Silver–Metal Oxide Materials
| |
− | | |
− | ===2.4.3.3 Silver–Graphite (GRAPHOR)-Materials===
| |
− | Ag/C (GRAPHOR) contact materials are usually produced by powder metallurgy
| |
− | with graphite contents of 2 – 5 wt% ''(Table 2.32)''. The earlier typical
| |
− | manufacturing process of single pressed tips by pressing - sintering - repressing
| |
− | (PSR) has been replaced in Europe for quite some time by extrusion. In North
| |
− | America and some other regions however the PSR process is still used to some
| |
− | extend mainly for cost reasons.
| |
− | | |
− | The extrusion of sintered billets is now the dominant manufacturing method for
| |
− | semi-finished AgC materials ''(Figs. 2.126 – 2.129)''. The hot extrusion process
| |
− | results in a high density material with graphite particles stretched and oriented in
| |
− | the extrusion direction ''(Figs. 2.130 – 2.133)''. Depending on the extrusion
| |
− | method in either rod or strip form the graphite particles can be oriented in the
| |
− | finished contact tips perpendicular (GRAPHOR) or parallel (GRAPHOR D) to the
| |
− | switching contact surface ''(Figs. 2.131 and 2.132)''.
| |
− | | |
− | Since the graphite particles in the Ag matrix of Ag/C materials prevent contact
| |
− | tips from directly being welded or brazed, a graphite free bottom layer is
| |
− | required. This is achieved by either burning out (de-graphitizing) the graphite
| |
− | selectively on one side of the tips or by compound extrusion of a Ag/C billet
| |
− | covered with a fine silver shell.
| |
− | | |
− | Ag/C contact materials exhibit on the one hand an extremely high resistance to
| |
− | contact welding but on the other have a low arc erosion resistance. This is
| |
− | caused by the reaction of graphite with the oxygen in the surrounding
| |
− | atmosphere at the high temperatures created by the arcing. The weld resistance
| |
− | is especially high for materials with the graphite particle orientation parallel to the
| |
− | arcing contact surface. Since the contact surface after arcing consists of pure
| |
− | silver the contact resistance stays consistently low during the electrical life of the
| |
− | contact parts.
| |
− | | |
− | A disadvantage of the Ag/C materials is their rather high erosion rate. In materials
| |
− | with parallel graphite orientation this can be improved if part of the graphite is
| |
− | incorporated into the material in the form of fibers (GRAPHOR DF), ''(Fig. 2.133)''.
| |
− | The weld resistance is determined by the total content of graphite particles.
| |
− | | |
− | Ag/C tips with vertical graphite particle orientation are produced in a specific
| |
− | sequence: Extrusion to rods, cutting of double thickness tips, burning out of
| |
− | graphite to a controlled layer thickness, and a second cutting to single tips.
| |
− | Such contact tips are especially well suited for applications which require both,
| |
− | a high weld resistance and a sufficiently high arc erosion resistance ''(Table 2.33)''.
| |
− | For attachment of Ag/C tips welding and brazing techniques are applied.
| |
− | | |
− | welding the actual process depends on the material's graphite orientation. For
| |
− | Ag/C tips with vertical graphite orientation the contacts are assembled with
| |
− | single tips. For parallel orientation a more economical attachment starting with
| |
− | contact material in strip or profile tape form is used in integrated stamping and
| |
− | welding operations with the tape fed into the weld station, cut off to tip form and
| |
− | then welded to the carrier material before forming the final contact assembly
| |
− | part. For special low energy welding the Ag/C profile tapes GRAPHOR D and DF
| |
− | can be pre-coated with a thin layer of high temperature brazing alloys such as
| |
− | CuAgP.
| |
− | | |
− | In a rather limited way, Ag/C with 2 – 3 wt% graphite can be produced in wire
| |
− | form and headed into contact rivet shape with low head deformation ratios.
| |
− | | |
− | The main applications for Ag/C materials are protective switching devices such
| |
− | as miniature molded case circuit breakers, motor-protective circuit breakers,
| |
− | and fault current circuit breakers, where during short circuit failures highest
| |
− | resistance against welding is required ''(Table 2.34)''. For higher currents the low
| |
− | arc erosion resistance of Ag/C is compensated by asymmetrical pairing with
| |
− | more erosion resistant materials such as Ag/Ni and Ag/W.
| |
− | | |
− | Fig. 2.126:
| |
− | Strain hardening
| |
− | of Ag/C 96/4 D
| |
− | by cold working
| |
− | | |
− | Fig. 2.127:
| |
− | Softening of Ag/C 96/4 D after
| |
− | annealing
| |
− | | |
− | Fig. 2.128: Strain hardening
| |
− | of Ag/C DF by cold working
| |
− | | |
− | Fig. 2.129: Softening
| |
− | of Ag/C DF after annealing
| |
− | | |
− | Fig. 2.130: Micro structure of Ag/C 97/3: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag backing layer
| |
− | | |
− | Fig. 2.131: Micro structure of Ag/C 95/5: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag backing layer
| |
− | | |
− | Fig. 2.132: Micro structure of Ag/C 96/4 D: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag backing layer
| |
− | | |
− | Fig. 2.133: Micro structure of Ag/C DF: a) perpendicular to extrusion direction
| |
− | b) parallel to extrusion direction, 1) Ag/C contact layer, 2) Ag/Ni 90/10 backing layer
| |
− | | |
− | Table 2.32: Physical Properties of Silver–Graphite (GRAPHOR) Contact Materials
| |
− | | |
− | Table 2.33: Contact and Switching properties of Silver–Graphite (GRAPHOR) Contact Materials
| |
− | | |
− | Table 2.34: Application Examples and Forms of Supply of Silver–
| |
− | Graphite (GRAPHOR) Contact Materials
| |
− | | |
− | Pre-Production of Contact Materials
| |
| (Bild) | | (Bild) |
| | | |
− | ===2.5 Tungsten and Molybdenum Based Materials===
| + | [[de:Kontaktwerkstoffe_für_die_Elektrotechnik]] |
− | | |
− | ===2.5.1 Tungsten and Molybdenum (Pure Metals)===
| |
− | Tungsten is characterized by its advantageous properties of high melting and
| |
− | boiling points, sufficient electrical and thermal conductivity and high hardness
| |
− | and density ''(Table 2.35)''. It is mainly used in the form of brazed contact tips for
| |
− | switching duties that require a rapid switching sequence such as horn contacts
| |
− | for cars and trucks.
| |
− | | |
− | Molybdenum has a much lesser importance as a contact material since it is less
| |
− | resistant against oxidation than tungsten.
| |
− | Both metals are however used in large amounts as components in composite
| |
− | materials with silver and copper.
| |
− | | |
− | Table 2.35: Mechanical Properties of Tungsten and Molybdenum
| |
− | | |
− | ===2.5.2 Silver–Tungsten (SIWODUR) Materials===
| |
− | Ag/W (SIWODUR) contact materials combine the high electrical and thermal
| |
− | conductivity of silver with the high arc erosion resistance of the high melting
| |
− | tungsten metal ''(Table 2.36)''. The manufacturing of materials with typically
| |
− | 50-80 wt% tungsten is performed by the powder metallurgical processes of
| |
− | liquid phase sintering or by infiltration. Particle size and shape of the starting
| |
− | powders are determining the micro structure and the contact specific properties
| |
− | of this material group ''(Figs. 2.134 and 2.135) (Table 2.37)''.
| |
− | | |
− | During repeated switching under arcing loads tungsten oxides and mixed
| |
− | oxides (silver tungstates – Ag<sub>2</sub> WO<sub>4</sub> ) are formed on the Ag/W surface creating 2 4
| |
− | poorly conducting layers which increase the contact resistance and by this the
| |
− | temperature rise during current carrying. Because of this fact the Ag/W is paired
| |
− | in many applications with Ag/C contact parts.
| |
− | | |
− | Silver–tungsten contact tips are used in a variety of shapes and are produced for
| |
− | the ease of attachment with a fine silver backing layer and quite often an
| |
− | additional thin layer of a brazing alloy. The attachment to contact carriers is
| |
− | usually done by brazing, but also by direct resistance welding for smaller tips.
| |
− | | |
− | Ag/W materials are mostly used as the arcing contacts in disconnect switches
| |
− | for higher loads and as the main contacts in small and medium duty power
| |
− | switches and industrial circuit breakers ''(Table 2.38)''. In north and south america
| |
− | they are also used in large volumes in miniature circuit breakers of small to
| |
− | medium current ratings in domestic wiring as well as for commercial power
| |
− | distribution.
| |
− | | |
− | ===2.5.3 Silver–Tungsten Carbide (SIWODUR C) Materials===
| |
− | This group of contact materials contains the typically 40-65 wt-% of the very
| |
− | hard and erosion wear resistant tungsten carbide and the high conductivity silver
| |
− | ''(Fig. 2.135) (Table 2.36)''. Compared to Ag/W the Ag/WC (SIWODUR C)
| |
− | materials exhibit a higher resistance against contact welding ''(Table 2.37)''. The
| |
− | rise in contact resistance experienced with Ag/W is less pronounced in Ag/WC
| |
− | because during arcing a protective gas layer of CO is formed which limits the
| |
− | reaction of oxygen on the contact surface and therefore the formation of metal
| |
− | oxides.
| |
− | | |
− | Higher requirements on low temperature rise can be fulfilled by adding a small
| |
− | amount of graphite which however increases the arc erosion. Silver–tungsten
| |
− | carbide–graphite materials with for example 27 wt% WC and
| |
− | 3 wt% graphite or 16 wt% WC and 2 wt% graphite are manufactured using the
| |
− | single tip press-sinter-repress (PSR) process ''(Fig. 2.136)''.
| |
− | | |
− | The applications of Ag/WC contacts are similar to those for Ag/W ''(Table 2.38)''.
| |
− | | |
− | ===2.5.4 Silver–Molybdenum (SILMODUR) Materials===
| |
− | Ag/Mo materials with typically 50-70 wt% molybdenum are usually produced by
| |
− | the powder metallurgical infiltration process ''(Fig. 2.137) (Table 2.36)''. Their
| |
− | contact properties are similar to those of Ag/W materials ''(Table 2.37)''. Since the
| |
− | molybdenum oxide is thermally less stable than tungsten oxide the self-cleaning
| |
− | effect of Ag/Mo contact surface during arcing is more pronounced and the
| |
− | contact resistance remains lower than that of Ag/W. The arc erosion resistance
| |
− | of Ag/Mo however is lower than the one for Ag/W materials. The main
| |
− | applications for Ag/Mo contacts are in equipment protecting switching devices
| |
− | ''(Table 2.38)''.
| |
− | | |
− | Fig. 2.134: Micro structure of Ag/W 25/75
| |
− | | |
− | Fig. 2.135: Micro structure of Ag/WC 50/50
| |
− | | |
− | Fig. 2.136: Micro structure of Ag/WC27/C3
| |
− | | |
− | Fig. 2.137: Micro structure of Ag/Mo 35/65
| |
− | | |
− | Table 2.36: Physical Properties of Contact Materials Based on Silver–Tungsten (SIWODUR),
| |
− | Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)
| |
− | | |
− | Table 2.37: Contact and Switching Properties of Contact Materials Based on Silver – Tungsten
| |
− | (SIWODUR), Silver–Tungsten Carbide (SIWODUR C)
| |
− | and Silver Molybdenum (SILMODUR)
| |
− | | |
− | Table 2.38: Application Examples and Forms of Supply for Contact Materials Based
| |
− | on Silver–Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C)
| |
− | and Silver Molybdenum (SILMODUR)
| |
− | | |
− | ===2.5.5 Copper–Tungsten (CUWODUR) Materials===
| |
− | Copper–tungsten (CUWODUR) materials with typically 50-85 wt% tungsten are
| |
− | produced by the infiltration process with the tungsten particle size selected
| |
− | according to the end application ''(Figs. 2.138 – 2.141) (Table 2.39)''. To increase
| |
− | the wettability of the tungsten skeleton by copper a small amount of nickel
| |
− | < 1 wt% is added to the starting powder mix.
| |
− | | |
− | W/Cu materials exhibit a very high arc erosion resistance ''(Table 2.40)''.
| |
− | Compared to silver–tungsten materials they are however less suitable to carry
| |
− | permanent current.
| |
− | | |
− | With a solid tungsten skeleton as it is the case for W/C infiltrated materials with
| |
− | 70-85 wt% tungsten the lower melting component copper melts and vaporizes
| |
− | in the intense electrical arc. At the boiling point of copper (2567°C) the still solid
| |
− | tungsten is efficiently “cooled” and remains pretty much unchanged.
| |
− | | |
− | During very high thermal stress on the W/Cu contacts, for example during short
| |
− | circuit currents > 40 kA the tungsten skeleton requires special high mechanical
| |
− | strength. For such applications a high temperature sintering of tungsten from
| |
− | selected particle size powder is applied before the usual infiltration with copper
| |
− | (example: CUWODUR H).
| |
− | | |
− | For high voltage load switches the most advantageous contact system consists
| |
− | of a contact tulip and a contact rod. Both contact assemblies are made usually
| |
− | from the mechanically strong and high conductive CuCrZr material and W/Cu as
| |
− | the arcing tips. The thermally and mechanically highly stressed attachment
| |
− | between the two components is often achieved by utilizing electron beam
| |
− | welding or capacitor discharge percussion welding. Other attachment methods
| |
− | include brazing and cast-on of copper followed by cold forming steps to
| |
− | increase hardness and strength.
| |
− | | |
− | The main application areas for CUWODUR materials are as arcing contacts in
| |
− | load and high power switching in medium and high voltage switchgear as well
| |
− | as electrodes for spark gaps and over voltage arresters ''(Table 2.41)''.
| |
− | | |
− | Table 2.39: Physical Properties of Copper–Tungsten (CUWODUR) Contact Materials
| |
− | | |
− | Fig. 2.139: Micro structure of W/Cu 70/30 G Fig. 2.140: Micro structure of W/Cu 70/30 H
| |
− | | |
− | Fig. 2.138: Micro structure of W/Cu 70/30 F Fig. 2.141: Micro structure of W/Cu 80/20 H
| |
− | | |
− | Manufacturing of Contact Parts for
| |
− | Medium and High Voltage Switchgear
| |
− | | |
− | Table 2.40: Contact and Switching Properties of Copper–Tungsten
| |
− | (CUWODUR) Contact Materials
| |
− | | |
− | Table 2.41: Application Examples and Forms of Supply for Tungsten–
| |
− | Copper (CUWODUR) Contact Materials
| |
− | | |
− | ===2.6 Special Contact Materials (VAKURIT) for Vacuum Switches===
| |
− | The trade name VAKURIT is assigned to a family of low gas content contact
| |
− | materials developed for the use in vacuum switching devices ''(Table 2.42)''.
| |
− | | |
− | ===2.6.1 Low Gas Content Materials Based on Refractory Metals===
| |
− | Contact materials of W/Cu, W/Ag, WC/Ag, or Mo/Cu can be used in vacuum
| |
− | switches if their total gas content does not exceed approximately 150 ppm. In
| |
− | the low gas content W/Cu (VAKURIT) material mostly used in vacuum contactors
| |
− | the high melting W skeleton is responsible for the high erosion resistance when
| |
− | combined with the high conductivity copper component which evaporates
| |
− | already in noticeable amounts at temperatures around 2000 °C.
| |
− | | |
− | Since there is almost no solubility of tungsten, tungsten carbide, or molybdenum
| |
− | in copper or silver the manufacturing of these material is performed powdermetallurgically.
| |
− | The W, WC, or Mo powders are pressed and sintered and then
| |
− | infiltrated with low gas content Cu or Ag. The content of the refractory metals is
| |
− | typically between 60 and 85 wt% ''(Figs. 2.142 and 2.143)''.
| |
− | | |
− | By adding approximately 1 wt% antimony the chopping current, i.e. the abrupt
| |
− | current decline shortly before the natural current-zero, can be improved for
| |
− | W/Cu (VAKURIT) materials ''(Table 2.43)''.
| |
− | The contact components mostly used in vacuum contactors are usually shaped
| |
− | as round discs. These are then attached by brazing in a vacuum environment to
| |
− | their contact carriers ''(Table 2.44)''.
| |
− | | |
− | ===2.6.2 Low Gas Content Materials Based on Copper-Chromium===
| |
− | As contact materials in vacuum interupters in medium voltage devices low gas
| |
− | materials based on Cu/Cr have gained broad acceptance. The typical chromium
| |
− | contents are between 25 and 55 wt% ''(Figs. 2.144 and 2.145)''. During the
| |
− | powder metallurgical manufacturing a mix of chromium and copper powders is
| |
− | pressed into discs and subsequently sintering in a reducing atmosphere or
| |
− | vacuum below the melting point of copper. This step is followed by cold or hot
| |
− | re-pressing. Depending on the composition the Cu/Cr (VAKURIT) materials
| |
− | combine a relatively high electrical and thermal conductivity with high dielectric
| |
− | stability. They exhibit a low arc erosion rate and good resistance against welding
| |
− | as well as favorable values of the chopping current in medium voltage load
| |
− | switches, caused by the combined effects of the two components, copper and
| |
− | chromium ''(Table 2.43)''.
| |
− | | |
− | The switching properties of Cu/Cr (VAKURIT) materials are dependent on the
| |
− | purity of the Cr metal powders and especially the type and quantity of impurities
| |
− | contained in the chromium powder used. Besides this the particle size and
| |
− | distribution of the Cr powder are of high importance. Because of the getter
| |
− | activity of chromium a higher total gas content of up to about 650 ppm
| |
− | compared to the limits in refractory based materials can be tolerated in these
| |
− | Cu/Cr contact materials. Besides the more economical sinter technology also
| |
− | infiltration and vacuum arc melting are used to manufacture these materials.
| |
− | Cu/Cr contacts are supplied in the shape of discs or rings which often also
| |
− | contain slots especially for vacuum load switches in medium voltage devices
| |
− | ''(Table 2.44)''. Increased applications of round discs can also be observed for low
| |
− | voltage vacuum contactors.
| |
− | | |
− | Table 2.42: Physical Properties of the Low Gas Materials (VAKURIT) for Vacuum Switches
| |
− | | |
− | Fig. 2.142: Micro structure of W/Cu 30Sb1
| |
− | – low gas
| |
− | | |
− | Fig. 2.143: Micro structure of WC/Ag 50/50
| |
− | – low gas
| |
− | | |
− | Fig. 2.144: Micro structure of Cu/Cr 75/25
| |
− | – low gas
| |
− | | |
− | Fig. 2.145: Micro structure of Cu/Cr 50/50
| |
− | – low gas
| |
− | | |
− | Table 2.43: Contact and Switching Properties of VAKURIT Materials
| |
− | | |
− | Table 2.44: Application Examples and Form of Supply for VAKURIT Materials
| |
− | | |
− | ===References===
| |
− | | |
− | <ref>Vinaricky, E.(Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen.
| |
− | Springer-Verlag, Berlin, Heidelberg etc. 2002</ref>
| |
The contact parts are important components in switching devices. They have to maintain their function from the new state until the end of the functional life of the devices.
The requirements on contacts are rather broad. Besides typical contact properties such as
- High arc erosion resistance
- High resistance against welding
- Low contact resistance
- Good arc moving properties
- Good arc extinguishing capability
They have to exhibit physical, mechanical and chemical properties like high electrical and thermal conductivity, high hardness, high corrosion resistance etc. and besides this, should have good mechanical workability and also be suitable for good weld and brazing attachment to contact carriers. In addition they must be made from environmentally friendly materials.
Materials suited for use as electrical contacts can be divided into the following groups based on their composition and metallurgical structure:
- Pure metals
- Alloys
- Composite materials
Pure metals
Within this group, silver has the greatest importance for switching devices in the higher energy technology. Other precious metals such as gold and platinum are only used in applications for the information technology in the form of thin surface layers. As a nonprecious metal, tungsten is used for some special applications such as, for example, automotive horn contacts. In some rarer cases, pure copper is used, but mainly paired to a silver-based contact material.
Alloys
Besides these few pure metals, a larger number of alloy materials made by melt technology are available for the use as contacts. An alloy is characterized by the fact, that its components are completely or partially soluble in each other in the solid state. Phase diagrams for multiple metal compositions show the number and type of the crystal structure as a function of the temperature and composition of the alloying components.
They indicate the boundaries of liquid and solid phases and define the parameters of solidification.
Alloying allows to improve the properties of one material at the cost of changing them for the second material. As an example, the hardness of a base metal may be increased while at the same time the electrical conductivity decreases with even small additions of the second alloying component.
Composite Materials
Composite materials are a material group whose properties are of great importance for electrical contacts that are used in switching devices for higher
electrical currents.
Those used in electrical contacts are heterogeneous materials, composed of two or more uniformly dispersed components, in which the largest volume portion consists of a metal.
The properties of composite materials are determined mainly independent from each other by the properties of their individual components. Therefore it is, for example, possible to combine the high melting point and arc erosion resistance of tungsten with the low melting and good electrical conductivity of copper or the high conductivity of silver with the weld resistant metalloid graphite. Figure 1 shows the schematic manufacturing processes from powder blending to contact material. Three basic process variations are typically applied:
- Sintering without liquid phase (Press-Sinter-Repress, PSR)
- Sintering with liquid phase
- Infiltration (Press-Sinter-Infiltrate, PSI)
During sintering without a liquid phase (left side of schematic), the powder mix is first densified by pressing, then undergoes a heat treatment (sintering) and eventually is re-pressed again to further increase the density. The sintering atmosphere depends on the material components and later application; a vacuum is used for example for the low gas content material Cu/Cr. This process is used for individual contact parts and also termed press-sinter-repress (PSR). For materials with high silver content, the starting point before pressing is mostly a large block (or billet) which is then, after sintering, hot extruded into wire, rod or strip form. The extrusion further increases the density of these composite materials and contributes to higher arc erosion resistance. Materials such as Ag/Ni, Ag/MeO and Ag/C are typically produced by this process.
Sintering with liquid phase has the advantage of shorter process times due to the accelerated diffusion and also results in near-theoretical densities of the composite material. To ensure the shape stability during the sintering process, it
is however necessary to limit the volume content of the liquid phase material.
As opposed to the liquid phase sintering, which has limited use for electrical contact manufacturing, the Infiltration process as shown on the right side of the schematic, has a broad practical range of applications. In this process the powder of the higher melting component, sometimes also as a powder mix with a small amount of the second material, is pressed into parts. Then, right after sintering, the porous skeleton is infiltrated with liquid metal of the second material. The fill-up process of the pores happens through capillary forces. This process reaches, after the infiltration, near-theoretical density without subsequent pressing and is widely used for Ag- and Cu-refractory contacts. For Ag/W or Ag/WC contacts, controlling the amount or excess on the bottom side of the contact of the infiltration metal Ag, results in contact tips that can be easily attached to their carriers by resistance welding. For larger Cu/W contacts, additional machining is often used to obtain the final shape of the contact component.
Gold Based Materials
Pure Gold is besides Platinum the chemically most stable of all precious metals. In its pure form, it is not very suitable for use as a contact material in electromechanical devices because of its tendency to stick and cold-weld at even low contact forces. In addition, it is not hard or strong enough to resist mechanical wear and exhibits high material losses under electrical arcing loads. This limits its use in form of thin electroplated or vacuum deposited layers.
Main Article: Gold Based Materials
Platinum Metal Based Materials
The platinum group metals include the elements Pt, Pd, Rh, Ru, Ir and Os (Table 1). For electrical contacts, platinum and palladium have practical significance as base alloy materials and ruthenium and iridium are used as alloying components. Pt and Pd have similar corrosion resistance as gold but due to their catalytical properties, they tend to polymerize adsorbed organic vapors on contact surfaces. During frictional movement between contact surfaces, the polymerized compounds known as “brown powder” are formed, which can lead to a significant increase in contact resistance. Therefore Pt and Pd are typically used as alloys and are rather not used in their pure form for electrical contact applications.
Main Article: Platinum Metal Based Materials
Silver Based Materials
Main Article: Silver Based Materials
Tungsten and Molybdenum Based Materials
Main Article: Tungsten and Molybdenum Based Materials
Contact Materials for Vacuum Switches
The low gas content contact materials are developed for the use in vacuum switching devices.
Main Article: Contact Materials for Vacuum Switches
References
Vinaricky, E.(Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen.
Springer-Verlag, Berlin, Heidelberg etc. 2002
Lindmayer, M.: Schaltgeräte-Grundlagen, Aufbau, Wirkungsweise.
Springer-Verlag, Berlin, Heidelberg, New York, Tokio, 1987
Rau, G.: Metallische Verbundwerkstoffe. Werkstofftechnische
Verlagsgesellschaft, Karlsruhe 1977
Schreiner, H.: Pulvermetallurgie elektrischer Kontakte. Springer-Verlag
Berlin, Göttingen, Heidelberg, 1964
Hansen. M.; Anderko, K.: Constitution of Binary Alloys. New York:
Mc Graw-Hill, 1958
Shunk, F.A.: Constitution of Binary Alloy. 2 Suppl. New York; Mc Graw-Hill, 1969
Edelmetall-Taschenbuch. ( Herausgeber Degussa AG, Frankfurt a. M.),
Heidelberg, Hüthig-Verlag, 1995
Rau, G.: Elektrische Kontakte-Werkstoffe und Technologie. Eigenverlag G. Rau
GmbH & Co., Pforzheim, 1984
Heraeus, W. C.: Werkstoffdaten. Eigenverlag W.C. Heraeus, Hanau, 1978
Linde, J.O.: Elektrische Widerstandseigenschaften der verdünnten Legierungen
des Kupfers, Silbers und Goldes. Lund: Hakan Ohlsson, 1938
Engineers Relay Handbook, RSIA, 2006
Großmann, H. Saeger, K. E.; Vinaricky, E.: Gold and Gold Alloys in Electrical
Engineering. in: Gold, Progress in Chemistry, Biochemistry and Technology. John
Wiley & Sons, Chichester etc, (1999) 199-236
Gehlert, B.: Edelmetall-Legierungen für elektrische Kontakte.
Metall 61 (2007) H. 6, 374-379
Aldinger, F.; Schnabl, R.: Edelmetallarme Kontakte für kleine Ströme.
Metall 37 (1983) 23-29
Bischoff, A.; Aldinger, F.: Einfluss geringer Zusätze auf die mechanischen
Eigenschaften von Au-Ag-Pd-Legierungen. Metall 36 (1982) 752-765
Wise, E.M.: Palladium, Recovery, Properties and Uses. New York, London:
Academic Press 1968
Savitskii, E.M.; Polyakova, V.P.; Tylina, M.A.: Palladium Alloys, Primary Sources.
New York: Publishers 1969
Gehlert, B.: Lebensdaueruntersuchungen von Edelmetall Kontaktwerkstoff-
Kombinationen für Schleifringübertrager. VDE-Fachbericht 61, (2005) 95-100
Holzapfel,C.: Verschweiß und elektrische Eigenschaften von
Schleifringübertragern. VDE-Fachbericht 67 (2011) 111-120
Schnabl, R.; Gehlert, B.: Lebensdauerprüfungen von Edelmetall-
Schleifkontaktwerkstoffen für Gleichstrom Kleinmotoren.
Feinwerktechnik & Messtechnik (1984) 8, 389-393
Kobayashi, T.; Koibuchi, K.; Sawa, K.; Endo, K.; Hagino, H.: A Study of Lifetime
of Au-plated Slip-Ring and AgPd Brush System for Power Supply.
th Proc. 24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 537-542
Harmsen, U.; Saeger K.E.: Über das Entfestigungsverhalten von Silber
verschiedener Reinheiten. Metall 28 (1974) 683-686
Behrens, V.; Michal, R.; Minkenberg, J.N.; Saeger, K.E.: Abbrand und
Kontaktwiderstandsverhalten von Kontaktwerkstoffen auf Basis von Silber-
Nickel. e.& i. 107. Jg. (1990), 2, 72-77
Behrens, V.: Silber/Nickel und Silber/Grafit- zwei Spezialisten auf dem Gebiet
der Kontaktwerkstoffe. Metall 61 (2007) H.6, 380-384
Rieder, W.: Silber / Metalloxyd-Werkstoffe für elektrische Kontakte,
VDE - Fachbericht 42 (1991) 65-81
Harmsen,U.: Die innere Oxidation von AgCd-Legierungen unter
Sauerstoffdruck.
Metall 25 (1991), H.2, 133-137
Muravjeva, E.M.; Povoloskaja, M.D.: Verbundwerkstoffe Silber-Zinkoxid und
Silber-Zinnoxid, hergestellt durch Oxidationsglühen.
Elektrotechnika 3 (1965) 37-39
Behrens, V.; Honig Th.; Kraus, A.; Michal, R.; Saeger, K.-E.; Schmidberger, R.;
Staneff, Th.: Eine neue Generation von AgSnO2 -Kontaktwerkstoffen.
VDE-Fachbericht 44, (1993) 99-114
Braumann, P.; Lang, J.: Kontaktverhalten von Ag-Metalloxiden für den Bereich
hoher Ströme. VDE-Fachbericht 42, (1991) 89-94
Hauner, F.; Jeannot, D.; Mc Neilly, U.; Pinard, J.: Advanced AgSnO Contact 2
th Materials for High Current Contactors. Proc. 20 Int. Conf. on Electr. Contact
Phenom., Stockholm 2000, 193-198
Wintz, J.-L.; Hardy, S.; Bourda, C.: Influence on the Electrical Performances of
Assembly Process, Supports Materials and Production Means for AgSnO2 .
Proc.24th Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 75-81
Behrens, V.; Honig, Th.; Kraus, A.; Michal, R.: Schalteigenschaften von
verschiedenen Silber-Zinnoxidwerkstoffen in Kfz-Relais. VDE-Fachbericht 51
(1997) 51-57
Schöpf, Th.: Silber/Zinnoxid und andere Silber-Metalloxidwerkstoffe in
Netzrelais. VDE-Fachbericht 51 (1997) 41-50
Schöpf, Th.; Behrens, V.; Honig, Th.; Kraus, A.: Development of Silver Zinc
th Oxide for General-Purpose Relays. Proc. 20 Int. Conf. on Electr. Contacts,
Stockholm 2000, 187-192
Braumann, P.; Koffler, A.: Einfluss von Herstellverfahren, Metalloxidgehalt und
Wirkzusätzen auf das Schaltverhalten von Ag/SnO in Relais. 2
VDE-Fachbericht 59, (2003) 133-142
Kempf, B.; Braumann, P.; Böhm, C.; Fischer-Bühner, J.: Silber-Zinnoxid-
Werkstoffe: Herstellverfahren und Eigenschaften. Metall 61(2007) H. 6, 404-408
Lutz, O.; Behrens, V.; Finkbeiner, M.; Honig, T.; Späth, D.: Ag/CdO-Ersatz in
Lichtschaltern. VDE-Fachbericht 61, (2005) 165-173
Lutz, O.; Behrens, V.; Wasserbäch, W.; Franz, S.; Honig, Th.; Späth,
D.; Heinrich, J.: Improved Silver/Tin Oxide Contact Materials for Automotive
th Applications. Proc.24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008,
88-93
Leung, C.; Behrens, V.: A Review of Ag/SnO Contact Materials and Arc Erosion. 2
th Proc.24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 82-87
Chen, Z.K.; Witter, G.J.: Comparison in Performance for Silver–Tin–Indium
Oxide Materials Made by Internal Oxidation and Powder Metallurgy.
th Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver, BC, Canada,
(2009) 167 – 176
Roehberg, J.; Honig, Th.; Witulski, N.; Finkbeiner, M.; Behrens, V.: Performance
of Different Silver/Tin Oxide Contact Materials for Applications in Low Voltage
th Circuit Breakers. Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver,
BC, Canada, (2009) 187 – 194
Muetzel, T.; Braumann, P.; Niederreuther, R.: Temperature Rise Behavior of
th Ag/SnO Contact Materials for Contactor Applications. Proc. 55 IEEE Holm 2
Conf. on Electrical Contacts, Vancouver, BC, Canada, (2009) 200 – 205
Lutz, O. et al.: Silber/Zinnoxid – Kontaktwerkstoffe auf Basis der Inneren
Oxidation fuer AC – und DC – Anwendungen.
VDE Fachbericht 65 (2009) 167 – 176
Harmsen, U.; Meyer, C.L.: Mechanische Eigenschaften stranggepresster Silber-
Graphit-Verbundwerkstoffe. Metall 21 (1967), 731-733
Behrens, V.: Mahle, E.; Michal, R.; Saeger, K.E.: An Advanced Silver/Graphite
th Contact Material Based on Graphite Fibre. Proc. 16 Int. Conf. on Electr.
Contacts, Loghborough 1992, 185-189
Schröder, K.-H.; Schulz, E.-D.: Über den Einfluss des Herstellungsverfahrens
th auf das Schaltverhalten von Kontaktwerkstoffen der Energietechnik. Proc. 7 Int.
Conf. on Electr. Contacts, Paris 1974, 38-45
Mützel, T.: Niederreuther, R.: Kontaktwerkstoffe für Hochleistungsanwendungen.
VDE-Bericht 67 (2011) 103-110
Lambert, C.; Cambon, G.: The Influence of Manufacturing Conditions and
Metalurgical Characteristics on the Electrical Behaviour of Silver-Graphite
th Contact Materials. Proc. 9 Int. Conf.on Electr. Contacts,
Chicago 1978, 401-406
Vinaricky, E.: Grundsätzliche Untersuchungen zum Abbrand- und
Schweißverhalten von Ag/C-Kontaktwerkstoffen. VDE-Fachbericht 47 (1995)
159-169
Agte, C.; Vacek, J.: Wolfram und Molybdän. Berlin: Akademie-Verlag 1959
Keil, A.; Meyer, C.-L.: Der Einfluß des Faserverlaufes auf die elektrische
Verschleißfestigkeit von Wolfram-Kontakten. ETZ 72, (1951) 343-346
Slade, P. G.: Electric Contacts for Power Interruption. A Review. Proc. 19 Int.
Conf. on Electric Contact Phenom. Nuremberg (Germany) 1998, 239-245
Slade, P. G.: Variations in Contact Resistance Resulting from Oxide Formation
and Decomposition in AgW and Ag-WC-C Contacts Passing Steady Currents
for Long Time Periods. IEEE Trans. Components, Hybrids and Manuf. Technol.
CHMT-9,1 (1986) 3-16
Slade, P. G.: Effect of the Electric Arc and the Ambient Air on the Contact
Resistance of Silver, Tungsten and Silver-Tungsten Contacts.
J.Appl.Phys. 47, 8 (1976) 3438-3443
Lindmayer, M.; Roth, M.: Contact Resistance and Arc-Erosion of W-Ag and
WC-Ag. IEEE Trans components, Hybrids and Manuf. Technol.
CHMT-2, 1 (1979) 70-75
Leung, C.-H.; Kim, H.J.: A Comparison of Ag/W, Ag/WC and Ag/Mo Electrical
Contacts. IEEE Trans. Components, Hybrids, Manuf. Technol.,
Vol. CHMT-7, 1 (1984) 69-75
Allen, S.E.; Streicher, E.: The Effect of Microstructure on the Electrical
th Performance of Ag-WC-C Contact Materials. Proc. 44 IEEE Holm Conf. on Electr.
Contacts, Arlington, VA, USA (1998), 276-285
Haufe, W.; Reichel, W.; Schreiner H.: Abbrand verschiedener W/Cu-Sinter-
Tränkwerkstoffe an Luft bei hohen Strömen. Z. Metallkd. 63 (1972) 651-654
Althaus, B.; Vinaricky, E.: Das Abbrandverhalten verschieden hergestellter
Wolfram-Kupfer-Verbundwerkstoffe im Hochstromlichtbogen.
Metall 22 (1968) 697-701
Gessinger, G.H.; Melton, K.N.: Burn-off Behaviour of WCu Contact Materials in an
Electric Arc. Powder Metall. Int. 9 (1977) 67-72
Magnusson, M.: Abbrandverhalten und Rißbildung bei WCu-Tränkwerkstoffen
unterschiedlicher Wolframteilchengröße. ETZ-A 98 (1977) 681-683
Heitzinger, F.; Kippenberg, H.; Saeger, K.E.; Schröder, K.H.: Contact Materials for
Vacuum Switching Devices. Proc. XVth ISDEIV, Darmstadt 1992, 273-278
Grill, R.; Müller, F.: Verbundwerkstoffe auf Wolframbasis für
Hochspannungsschaltgeräte. Metall 61 (2007) H. 6, 390-393
Slade, P.: G.: The Vacuum Interrupter- Theory; Design; and Application. CRC
Press, Boca Raton, FL (USA), 2008
Frey, P.; Klink, N.; Saeger, K.E.: Untersuchungen zum Abreißstromverhalten von
Kontaktwerkstoffen für Vakuumschütze. Metall 38 (1984) 647-651
Frey, P.; Klink, N.; Michal, R.; Saeger, K.E.: Metallurgical Aspects of Contact
Materials for Vacuum Switching Devices. IEEE Trans. Plasma Sc. 17, (1989) 743-
740
Slade, P.: Advances in Material Development for High Power Vacuum Interrupter
th Contacts. Proc.16 Int. Conf. on Electr. Contact Phenom.,
Loughborough 1992,1-10
Behrens, V.; Honig, Th.; Kraus, A.; Allen, S.: Comparison of Different Contact
th Materials for Low Voltage Vacuum Applications. Proc.19 Int. Conf. on Electr.
Contact Phenom., Nuremberg 1998, 247-251
Rolle, S.; Lietz, A.; Amft, D.; Hauner, F.: CuCr Contact Material for Low Voltage
th Vacuum Contactors. Proc. 20 int. Conf. on Electr. Contact. Phenom. Stockholm
2000, 179-186
Kippenberg, H.: CrCu as a Contact Material for Vacuum Interrupters.
th Proc.13 Int. Conf. on Electr. Contact Phenom. Lausanne 1986, 140-144
Hauner, F.; Müller, R.; Tiefel, R.: CuCr für Vakuumschaltgeräte-
Herstellungsverfahren, Eigenschaften und Anwendung.
Metall 61 (2007) H. 6, 385-389
Manufacturing Equipment for Semi-Finished Materials
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