Difference between revisions of "Contact Materials for Electrical Engineering"

From Electrical Contacts
Jump to: navigation, search
 
(86 intermediate revisions by 6 users not shown)
Line 1: Line 1:
−
===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
Line 13: Line 9:
 
*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)
Line 71: Line 42:
 
*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
 
−
the accelerated diffusion and also results in near-theoretical densities of the
 
  
−
Fig. 2.1: Powder-metallurgical manufacturing of composite materials (schematic)
+
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.
−
T = Melting point of the lower melting component
 
  
−
composite material. To ensure the shape stability during the sintering process it
+
''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.
 
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
 
−
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
 
−
alloying metal the melting is performed either under in a reducing atmosphere or
 
−
in a vacuum. The choice of alloying metals depends on the intended use of the
 
−
resulting contact material. The binary Au alloys with typically <10 wt% of other
 
−
precious metals such as Pt, Pd, or Ag or non-precious metals like Ni, Co, and
 
−
Cu are the more commonly used ones (Table 2.2). On one hand these alloy
 
−
additions improve the mechanical strength and electrical switching properties
 
−
but on the other hand reduce the electrical conductivity and chemical corrosion
 
−
resistance (Fig. 2.2) to varying degrees.
 
−
 
 
−
Under the aspect of reducing the gold content ternary alloys with a gold content
 
−
of approximately 70 wt% and additions of Ag and Cu or Ag and Ni resp., for
 
−
example AuAg25Cu5 or AuAg20Cu10 are used which exhibit for many
 
−
applications good mechanical stability while at the same time have sufficient
 
−
resistance against the formation of corrosion layers (Table 2.3). Other ternary
 
−
alloys based on the AuAg system are AuAg26Ni3 and AuAg25Pt6. These alloys
 
−
are mechanically similar to the AuAgCu alloys but have significantly higher
 
−
oxidation resistance at elevated temperatures (Table 2.4).
 
−
 
 
−
Caused by higher gold prices over the past years the development of alloys with
 
−
further reduced gold content had a high priority. The starting point has been the
 
−
AuPd system which has continuous solubility of the two components. Besides
 
−
the binary alloy of AuPd40 and the ternary one AuPd35Ag9 other multiple
 
−
component alloys were developed. These alloys typically have < 50 wt% Au and
 
−
often can be solution hardened in order to obtain even higher hardness and
 
−
tensile strength. They are mostly used in sliding contact applications.
 
−
 
 
−
Gold alloys are used in the form of welded wire or profile (also called weldtapes),
 
−
segments, contact rivets, and stampings produced from clad strip
 
−
materials. The selection of the bonding process is based on the cost for the
 
−
joining process, and most importantly on the economical aspect of using the
 
−
least possible amount of the expensive precious metal component.
 
−
 
 
−
Besides being used as switching contacts in relays and pushbuttons, gold
 
−
alloys are also applied in the design of connectors as well as sliding contacts for
 
−
potentiometers, sensors, slip rings, and brushes in miniature DC motors
 
−
(Table 2.5).
 
−
 
 
−
Table 2.3: Mechanical Properties of Gold and Gold-Alloys
 
−
 
 
−
Table 2.1: Commonly Used Grades of Gold
 
−
 
 
−
Table 2.2: Physical Properties of Gold and Gold-Alloys
 
−
 
 
−
Fig. 2.2:
 
−
Influence of 1-10 atomic% of different
 
−
alloying metals on the electrical resistivity of gold
 
−
(according to J. O. Linde)
 
−
 
 
−
Fig. 2.3:
 
−
Phase diagram
 
−
of goldplatinum
 
−
 
 
−
Fig. 2.4:
 
−
Phase diagram
 
−
of gold-silver
 
−
 
 
−
Fig. 2.5:
 
−
Phase diagram
 
−
of gold-copper
 
−
 
 
−
Fig. 2.6: Phase diagram of gold-nickel
 
−
 
 
−
Fig. 2.7: Phase diagram of gold-cobalt
 
−
 
 
−
Fig. 2.8:
 
−
Strain hardening
 
−
of Au by cold working
 
−
 
 
−
Fig. 2.9:
 
−
Softening of Au after annealing
 
−
for 0.5 hrs after 80%
 
−
cold working
 
−
 
 
−
Fig. 2.10:
 
−
Strain hardening of
 
−
AuPt10 by cold working
 
−
 
 
−
Fig. 2.11:
 
−
Strain hardening
 
−
of AuAg20 by cold working
 
−
 
 
−
Fig. 2.12:
 
−
Strain hardening of
 
−
AuAg30 by cold working
 
−
 
 
−
Fig. 2.13:
 
−
Strain hardening of AuNi5
 
−
by cold working
 
−
 
 
−
Fig. 2.14:
 
−
Softening
 
−
of AuNi5 after annealing
 
−
for 0.5 hrs after 80%
 
−
cold working
 
−
 
 
−
Fig. 2.15:
 
−
Strain hardening
 
−
of AuCo5 by cold working
 
−
 
 
−
Fig. 2.16:
 
−
Precipitation hardening of
 
−
AuCo5 at 400°C hardening
 
−
temperature
 
−
 
 
−
Fig. 2.17:
 
−
Strain hardening
 
−
of AuAg25Pt6 by cold working
 
−
 
 
−
Fig. 2.18:
 
−
Strain hardening
 
−
of AuAg26Ni3 by cold working
 
−
 
 
−
Fig. 2.19:
 
−
Softening
 
−
of AuAg26Ni3 after
 
−
annealing for 0.5 hrs
 
−
after 80% cold
 
−
working
 
−
 
 
−
Fig. 2.20:
 
−
Strain hardening of
 
−
AuAg25Cu5
 
−
by cold working
 
−
 
 
−
Fig. 2.21:
 
−
Strain hardening of
 
−
AuAg20Cu10
 
−
by cold working
 
−
 
 
−
Fig. 2.22:
 
−
Softening
 
−
of AuAg20Cu10 after
 
−
annealing for 0.5 hrs
 
−
after 80% cold working
 
−
 
 
−
Fig. 2.23:
 
−
Strain hardening of
 
−
AuCu14Pt9Ag4
 
−
by cold working
 
−
 
 
−
Fig. 2.24:
 
−
Precipitation
 
−
hardening of
 
−
AuCu14Pt9Ag4
 
−
at different
 
−
hardening
 
−
temperatures
 
−
after 50%
 
−
cold working
 
−
 
 
−
Table 2.4: Contact and Switching Properties of Gold and Gold Alloys
 
  
−
Table 2.5: Application Examples and Forms of Gold and Gold Alloys
+
==Gold Based Materials==
  
−
===2.3 Platinum Metal 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.
  
−
The platinum group metals include the elements Pt, Pd, Rh, Ru, Ir, and Os (Table
+
Main Article: [[Gold Based Materials| Gold Based Materials]]
−
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 because of 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 significantly
 
−
increase in contact resistance. Therefore Pt and Pd are typically used as alloys and
 
−
not in their pure form for electrical contact applications.
 
  
−
Rhodium is not used as a solid contact material but is applied for example as a
+
==Platinum Metal Based Materials==
−
electroplated layer in sliding contact systems. Ruthenium is mostly used as an alloying
 
−
component in the material PdRu15. The metals osmium and iridium have no practical
 
−
applications in electrical contacts.
 
  
−
Since Pd was for the longest time rather stable in price it was looked at as a substitute
+
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.
−
for the more expensive gold. This was followed by a steep increase in the Pd price
 
−
which caused a significant reduction in its use in electrical contacts. Today (2011) the
 
−
Pd price again is lower than that of gold.
 
  
−
Alloys of Pt with Ru, Ir, Ni, and W were widely used in electromechanical components
+
Main Article: [[Platinum Metal Based Materials| Platinum Metal Based Materials]]
−
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
 
−
state technology and the usage of these materials is greatly reduced. Pd alloys
 
−
however have a more significant importance. PdCu15 is widely used for example in
 
−
automotive flasher relays. Because of their resistance to sulfide formation PdAg alloys
 
−
are applied in various relay designs. The ability to thermally precipitation harden some
 
−
multi component alloys based on PdAgAuPt they find special usage in wear resistant
 
−
sliding contact applications. Pd44Ag38Cu15PtAuZn is a standard alloy in this group.
 
  
−
Platinum and palladium alloys are mainly used similar to the gold based materials in
+
==Silver Based Materials==
−
the form of welded wire and profile segments but rarely as contact rivets. Because of
 
−
the high precious metal prices joining technologies are used that allow the most
 
−
economic application of the contact alloy in the area where functionally needed.
 
−
Because of their resistance to material transfer they are used for DC applications and
 
−
due to their higher arc erosion resistance they are applied for medium electrical loads
 
−
up to about 30W in relays and switches (Table 2.10). Multi-component alloys based
 
−
on Pd with higher hardness and wear resistance are mainly used as spring arms in
 
−
sliding contact systems and DC miniature motors.
 
  
−
Table 2.6: Properties, Production Processes, and Application Forms for Platinum Metals
+
Main Article: [[Silver Based Materials| Silver Based Materials]]
  
−
Table 2.7: Physical Properties of the Platinum Metals and their Alloys
+
==Tungsten and Molybdenum Based Materials==
  
−
Table 2.8: Mechanical Properties of the Platinum Metals and their Alloys
+
Main Article: [[Tungsten and Molybdenum Based Materials| Tungsten and Molybdenum Based Materials]]
  
−
Fig. 2.25:
+
==Contact Materials for Vacuum Switches==
−
Influence of 1-
 
−
20 atom% of
 
−
different additive
 
−
metals on the
 
−
electrical
 
−
resistivity p of
 
−
platinum
 
−
(Degussa)
 
  
−
Fig. 2.26:
+
The low gas content contact materials are developed for the use in vacuum switching devices.  
−
Influence of 1-22 atom% of different
 
−
additive metals on the electrical
 
−
resistivity
 
−
p of palladium
 
  
−
Fig. 2.27:
+
Main Article: [[Contact Materials for Vacuum Switches| Contact Materials for Vacuum Switches]]
−
Phase diagram of
 
−
platinum-iridium
 
  
−
Fig. 2.28:
+
==References==
−
Phase diagram of
 
−
platinum-nickel
 
  
−
Fig. 2.29:
+
Vinaricky, E.(Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen.
−
Phase diagram
+
Springer-Verlag, Berlin, Heidelberg etc. 2002
−
of platinum-tungsten
 
  
−
Fig. 2.30:
+
Lindmayer, M.: Schaltgeräte-Grundlagen, Aufbau, Wirkungsweise.
−
Phase diagram of
+
Springer-Verlag, Berlin, Heidelberg, New York, Tokio, 1987
−
palladium-copper
 
  
−
Fig. 2.31:
+
Rau, G.: Metallische Verbundwerkstoffe. Werkstofftechnische
−
Strain
+
Verlagsgesellschaft, Karlsruhe 1977
−
hardening
 
−
of Pt by cold
 
−
working
 
  
−
Fig. 2.32:
+
Schreiner, H.: Pulvermetallurgie elektrischer Kontakte. Springer-Verlag
−
Softening of Pt after
+
Berlin, Göttingen, Heidelberg, 1964
−
annealing for 0.5 hrs
 
−
after 80%
 
−
cold working
 
  
−
Fig. 2.33:
+
Hansen. M.; Anderko, K.: Constitution of Binary Alloys. New York:
−
Strain hardening of PtIr5
+
Mc Graw-Hill, 1958
−
by cold working
 
  
−
Fig. 2.34:
+
Shunk, F.A.: Constitution of Binary Alloy. 2 Suppl. New York; Mc Graw-Hill, 1969
−
Softening of PtIr5 after annealing for 1 hr
 
−
after different degrees of cold working
 
  
−
Fig. 2.35:
+
Edelmetall-Taschenbuch. ( Herausgeber Degussa AG, Frankfurt a. M.),
−
Strain hardening
+
Heidelberg, Hüthig-Verlag, 1995
−
of PtNi8 by cold working
 
  
−
Fig. 2.36:
+
Rau, G.: Elektrische Kontakte-Werkstoffe und Technologie. Eigenverlag G. Rau
−
Softening of PtNi8 after
+
GmbH & Co., Pforzheim, 1984
−
annealing
 
−
for 1 hr after
 
−
80% cold working
 
  
−
Fig. 2.37:
+
Heraeus, W. C.: Werkstoffdaten. Eigenverlag W.C. Heraeus, Hanau, 1978
−
Strain hardening
 
−
of PtW5 by cold working
 
  
−
Fig. 2.38:
+
Linde, J.O.: Elektrische Widerstandseigenschaften der verdünnten Legierungen
−
Softening
+
des Kupfers, Silbers und Goldes. Lund: Hakan Ohlsson, 1938
−
of PtW5 after
 
−
annealing for 1hr
 
−
after 80% cold
 
−
working
 
  
−
Fig. 2.39:
+
Engineers Relay Handbook, RSIA, 2006
−
Strain hardening
 
−
of Pd 99.99 by cold working
 
  
−
Fig. 2.40:
+
Großmann, H. Saeger, K. E.; Vinaricky, E.: Gold and Gold Alloys in Electrical
−
Strain hardening
+
Engineering. in: Gold, Progress in Chemistry, Biochemistry and Technology. John
−
of PdCu15 by cold working
+
Wiley & Sons, Chichester etc, (1999) 199-236
  
−
Fig. 2.41:
+
Gehlert, B.: Edelmetall-Legierungen für elektrische Kontakte.
−
Softening
+
Metall 61 (2007) H. 6, 374-379
−
of PdCu15 after
 
−
annealing
 
−
for 0.5 hrs
 
  
−
Fig. 2.42:
+
Aldinger, F.; Schnabl, R.: Edelmetallarme Kontakte für kleine Ströme.
−
Strain hardening
+
Metall 37 (1983) 23-29
−
of PdCu40 by cold working
 
  
−
Fig. 2.43:
+
Bischoff, A.; Aldinger, F.: Einfluss geringer Zusätze auf die mechanischen
−
Softening
+
Eigenschaften von Au-Ag-Pd-Legierungen. Metall 36 (1982) 752-765
−
of PdCu40
 
−
after annealing
 
−
for 0.5 hrs after 80%
 
−
cold working
 
  
−
Fig. 2.44:
+
Wise, E.M.: Palladium, Recovery, Properties and Uses. New York, London:
−
Electrical resistivity p
+
Academic Press 1968
−
of PdCu alloys with and without an
 
−
annealing step for forming an ordered
 
−
phase
 
  
−
Table 2.9: Contact and Switching Properties
+
Savitskii, E.M.; Polyakova, V.P.; Tylina, M.A.: Palladium Alloys, Primary Sources.
−
of the Platinum Metals and their Alloys
+
New York: Publishers 1969
  
−
Table 2.10: Application Examples and Form
+
Gehlert, B.: Lebensdaueruntersuchungen von Edelmetall Kontaktwerkstoff-
−
of Supply for Platinum Metals and their Alloys
+
Kombinationen für Schleifringübertrager. VDE-Fachbericht 61, (2005) 95-100
  
−
===2.4 Silver Based Materials===
+
Holzapfel,C.: Verschweiß und elektrische Eigenschaften von
 +
Schleifringübertragern. VDE-Fachbericht 67 (2011) 111-120
  
−
===2.4.1 Pure Silver===
+
Schnabl, R.; Gehlert, B.: Lebensdauerprüfungen von Edelmetall-
−
Pure silver (also called fine silver) exhibits the highest electrical and thermal
+
Schleifkontaktwerkstoffen für Gleichstrom Kleinmotoren.
−
conductivity of all metals. It is also resistant against oxidation. Major disadvantages
+
Feinwerktechnik & Messtechnik (1984) 8, 389-393
−
are its low mechanical wear resistance, the low softening temperature,
 
−
and especially its strong affinity to sulfur and sulfur compounds. In the presence
 
−
of sulfur and sulfur containing compounds brownish to black silver sulfide layer
 
−
are formed on its surface. These can cause increased contact resistance or
 
−
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
 
−
weld under the influence of over-currents and the low resistance against
 
−
material transfer when switching DC loads. In humid environments and under
 
−
the influence of an electrical field silver can creep (silver migration) and cause
 
−
electrical shorting between adjacent current paths.
 
  
−
Table 2.11 shows the typically available quality grades of silver. In certain
+
Kobayashi, T.; Koibuchi, K.; Sawa, K.; Endo, K.; Hagino, H.: A Study of Lifetime
−
economic areas, i.e. China, there are additional grades with varying amounts of
+
of Au-plated Slip-Ring and AgPd Brush System for Power Supply.
−
impurities available on the market. In powder form silver is used for a wide
+
th Proc. 24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 537-542
−
variety of silver based composite contact materials. Different manufacturing
 
−
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.
 
−
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
 
−
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
+
Harmsen, U.; Saeger K.E.: Über das Entfestigungsverhalten von Silber
−
devices such as relays, pushbuttons, appliance and control switches for
+
verschiedener Reinheiten. Metall 28 (1974) 683-686
−
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
+
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
  
−
Table 2.12: Quality Criteria of Differently Manufactured Silver Powders
+
Behrens, V.: Silber/Nickel und Silber/Grafit- zwei Spezialisten auf dem Gebiet
 +
der Kontaktwerkstoffe. Metall 61 (2007) H.6, 380-384
  
−
Fig. 2.45:
+
Rieder, W.: Silber / Metalloxyd-Werkstoffe für elektrische Kontakte,
−
Strain hardening
+
VDE - Fachbericht 42 (1991) 65-81
−
of Ag 99.95 by cold working
 
  
−
Fig. 2.46:
+
Harmsen,U.: Die innere Oxidation von AgCd-Legierungen unter
−
Softening of Ag 99.95
+
Sauerstoffdruck.
−
after annealing for 1 hr after different
+
Metall 25 (1991), H.2, 133-137
−
degrees of strain hardening
 
  
−
===2.4.2 Silver Alloys===
+
Muravjeva, E.M.; Povoloskaja, M.D.: Verbundwerkstoffe Silber-Zinkoxid und
−
To improve the physical and contact properties of fine silver melt-metallurgical
+
Silber-Zinnoxid, hergestellt durch Oxidationsglühen.
−
produced silver alloys are used (Table 2.13). By adding metal components the
+
Elektrotechnika 3 (1965) 37-39
−
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===
+
Behrens, V.; Honig Th.; Kraus, A.; Michal, R.; Saeger, K.-E.; Schmidberger, R.;
−
Fine-Grain Silver (ARGODUR-Spezial) is defined as a silver alloy with an addition
+
Staneff, Th.: Eine neue Generation von AgSnO<sub>2</sub> -Kontaktwerkstoffen.
−
of 0.15 wt% of Nickel. Silver and nickel are not soluble in each other in solid
+
VDE-Fachbericht 44, (1993) 99-114
−
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
+
Braumann, P.; Lang, J.: Kontaktverhalten von Ag-Metalloxiden für den Bereich
−
silver. Compared to pure silver it exhibits a slightly increased hardness and
+
hoher Ströme. VDE-Fachbericht 42, (1991) 89-94
−
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===
+
Hauner, F.; Jeannot, D.; Mc Neilly, U.; Pinard, J.: Advanced AgSnO Contact 2
−
Using copper as an alloying component increases the mechanical stability of
+
th Materials for High Current Contactors. Proc. 20 Int. Conf. on Electr. Contact
−
silver significantly. The most important among the binary AgCu alloys is that of
+
Phenom., Stockholm 2000, 193-198
−
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
+
Wintz, J.-L.; Hardy, S.; Bourda, C.: Influence on the Electrical Performances of
−
AgCu alloys and improves arc erosion resistance and resistance against
+
Assembly Process, Supports Materials and Production Means for AgSnO<sub>2</sub> .
−
material transfer while at the same time however the tendency to oxide formation
+
Proc.24<sub>th</sub> Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 75-81
−
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
+
Behrens, V.; Honig, Th.; Kraus, A.; Michal, R.: Schalteigenschaften von
−
applications. From this group the material ARGODUR 27, an alloy of 98 wt% Ag
+
verschiedenen Silber-Zinnoxidwerkstoffen in Kfz-Relais. VDE-Fachbericht 51
−
with a 2 wt% Cu and nickel addition has found practical importance close to that
+
(1997) 51-57
−
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
+
Schöpf, Th.: Silber/Zinnoxid und andere Silber-Metalloxidwerkstoffe in
−
those applied for fine silver and fine grain silver.
+
Netzrelais. VDE-Fachbericht 51 (1997) 41-50
  
−
Hard-silver alloys are widely used for switching applications in the information
+
Schöpf, Th.; Behrens, V.; Honig, Th.; Kraus, A.: Development of Silver Zinc
−
and energy technology for currents up to 10 A, in special cases also for higher
+
th Oxide for General-Purpose Relays. Proc. 20 Int. Conf. on Electr. Contacts,
−
current ranges (Table 2.16).
+
Stockholm 2000, 187-192
  
−
Dispersion hardened alloys of silver with 0.5 wt% MgO and NiO (ARGODUR 32)
+
Braumann, P.; Koffler, A.: Einfluss von Herstellverfahren, Metalloxidgehalt und
−
are produced by internal oxidation. While the melt-metallurgical alloy is easy to
+
Wirkzusätzen auf das Schaltverhalten von Ag/SnO in Relais. 2
−
cold-work and form the material becomes very hard and brittle after dispersion
+
VDE-Fachbericht 59, (2003) 133-142
−
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
+
Kempf, B.; Braumann, P.; Böhm, C.; Fischer-Bühner, J.: Silber-Zinnoxid-
 +
Werkstoffe: Herstellverfahren und Eigenschaften. Metall 61(2007) H. 6, 404-408
  
−
ARGODUR 32 is mainly used in the form of contact springs that are exposed to
+
Lutz, O.; Behrens, V.; Finkbeiner, M.; Honig, T.; Späth, D.: Ag/CdO-Ersatz in
−
high thermal and mechanical stresses in relays, and contactors for aeronautic
+
Lichtschaltern. VDE-Fachbericht 61, (2005) 165-173
−
applications.
 
  
−
Fig. 2.47:
+
Lutz, O.; Behrens, V.; Wasserbäch, W.; Franz, S.; Honig, Th.; Späth,
−
Influence of 1-10 atom% of different
+
D.; Heinrich, J.: Improved Silver/Tin Oxide Contact Materials for Automotive
−
alloying metals on the electrical resistivity of
+
th Applications. Proc.24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008,
−
silver
+
88-93
  
−
Fig. 2.48:
+
Leung, C.; Behrens, V.: A Review of Ag/SnO Contact Materials and Arc Erosion. 2
−
Electrical resistivity p
+
th Proc.24 Int. Conf. on Electr. Contacts, Saint Malo, France 2008, 82-87
−
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
+
Chen, Z.K.; Witter, G.J.: Comparison in Performance for Silver–Tin–Indium
−
of Ag 99.97 after 80% cold working
+
Oxide Materials Made by Internal Oxidation and Powder Metallurgy.
−
and 1 hr annealing at 600°C
+
th Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver, BC, Canada,
 +
(2009) 167 – 176
  
−
Fig. 2.50: Fine grain microstructure
+
Roehberg, J.; Honig, Th.; Witulski, N.; Finkbeiner, M.; Behrens, V.: Performance
−
of AgNi0.15 after 80% cold working
+
of Different Silver/Tin Oxide Contact Materials for Applications in Low Voltage
−
and 1 hr annealing at 600°C
+
th Circuit Breakers. Proc. 55 IEEE Holm Conf. on Electrical Contacts, Vancouver,
 +
BC, Canada, (2009) 187 – 194
  
−
Fig. 2.51:
+
Muetzel, T.; Braumann, P.; Niederreuther, R.: Temperature Rise Behavior of
−
Phase diagram
+
th Ag/SnO Contact Materials for Contactor Applications. Proc. 55 IEEE Holm 2
−
of silver-nickel
+
Conf. on Electrical Contacts, Vancouver, BC, Canada, (2009) 200 – 205
  
−
Fig. 2.52:
+
Lutz, O. et al.: Silber/Zinnoxid – Kontaktwerkstoffe auf Basis der Inneren
−
Phase diagram
+
Oxidation fuer AC – und DC – Anwendungen.
−
of silver-copper
+
VDE Fachbericht 65 (2009) 167 – 176
  
−
Fig. 2.53:
+
Harmsen, U.; Meyer, C.L.: Mechanische Eigenschaften stranggepresster Silber-
−
Phase diagram of
+
Graphit-Verbundwerkstoffe. Metall 21 (1967), 731-733
−
silver-cadmium
 
  
−
Table 2.14: Mechanical Properties of Silver and Silver Alloys
+
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
  
−
Fig. 2.54:
+
Schröder, K.-H.; Schulz, E.-D.: Über den Einfluss des Herstellungsverfahrens
−
Strain hardening
+
th auf das Schaltverhalten von Kontaktwerkstoffen der Energietechnik. Proc. 7 Int.
−
of AgCu3
+
Conf. on Electr. Contacts, Paris 1974, 38-45
−
by cold working
 
  
−
Fig. 2.55:
+
Mützel, T.: Niederreuther, R.: Kontaktwerkstoffe für Hochleistungsanwendungen.
−
Softening of AgCu3
+
VDE-Bericht 67 (2011) 103-110
−
after annealing for 1 hr
 
−
after 80% cold working
 
  
−
Fig. 2.56:
+
Lambert, C.; Cambon, G.: The Influence of Manufacturing Conditions and
−
Strain hardening of AgCu5 by cold
+
Metalurgical Characteristics on the Electrical Behaviour of Silver-Graphite
−
working
+
th Contact Materials. Proc. 9 Int. Conf.on Electr. Contacts,
 +
Chicago 1978, 401-406
  
−
Fig. 2.57:
+
Vinaricky, E.: Grundsätzliche Untersuchungen zum Abbrand- und
−
Softening of AgCu5 after
+
Schweißverhalten von Ag/C-Kontaktwerkstoffen. VDE-Fachbericht 47 (1995)
−
annealing for 1 hr after 80% cold
+
159-169
−
working
 
  
−
Fig. 2.58:
+
Agte, C.; Vacek, J.: Wolfram und Molybdän. Berlin: Akademie-Verlag 1959
−
Strain hardening of AgCu 10
 
−
by cold working
 
  
−
Fig. 2.59:
+
Keil, A.; Meyer, C.-L.: Der Einfluß des Faserverlaufes auf die elektrische
−
Softening of AgCu10 after
+
Verschleißfestigkeit von Wolfram-Kontakten. ETZ 72, (1951) 343-346
−
annealing for 1 hr after 80% cold
 
−
working
 
  
−
Fig. 2.60:
+
Slade, P. G.: Electric Contacts for Power Interruption. A Review. Proc. 19 Int.
−
Strain hardening of AgCu28 by
+
Conf. on Electric Contact Phenom. Nuremberg (Germany) 1998, 239-245
−
cold working
 
  
−
Fig. 2.61:
+
Slade, P. G.: Variations in Contact Resistance Resulting from Oxide Formation
−
Softening of AgCu28
+
and Decomposition in AgW and Ag-WC-C Contacts Passing Steady Currents
−
after annealing for 1 hr after
+
for Long Time Periods. IEEE Trans. Components, Hybrids and Manuf. Technol.
−
80% cold working
+
CHMT-9,1 (1986) 3-16
  
−
Fig. 2.62:
+
Slade, P. G.: Effect of the Electric Arc and the Ambient Air on the Contact
−
Strain hardening of AgNi0.15
+
Resistance of Silver, Tungsten and Silver-Tungsten Contacts.
−
by cold working
+
J.Appl.Phys. 47, 8 (1976) 3438-3443
  
−
Fig. 2.63:
+
Lindmayer, M.; Roth, M.: Contact Resistance and Arc-Erosion of W-Ag and
−
Softening of AgNi0.15
+
WC-Ag. IEEE Trans components, Hybrids and Manuf. Technol.
−
after annealing for 1 hr after 80%
+
CHMT-2, 1 (1979) 70-75
−
cold working
 
  
−
Fig. 2.64:
+
Leung, C.-H.; Kim, H.J.: A Comparison of Ag/W, Ag/WC and Ag/Mo Electrical
−
Strain hardening of
+
Contacts. IEEE Trans. Components, Hybrids, Manuf. Technol.,
−
ARGODUR 27
+
Vol. CHMT-7, 1 (1984) 69-75
−
by cold working
 
  
−
Fig. 2.65:
+
Allen, S.E.; Streicher, E.: The Effect of Microstructure on the Electrical
−
Softening
+
th Performance of Ag-WC-C Contact Materials. Proc. 44 IEEE Holm Conf. on Electr.
−
of ARGODUR 27 after annealing
+
Contacts, Arlington, VA, USA (1998), 276-285
−
for 1 hr after 80% cold working
 
  
−
Table 2.15: Contact and Switching Properties of Silver and Silver Alloys
+
Haufe, W.; Reichel, W.; Schreiner H.: Abbrand verschiedener W/Cu-Sinter-
 +
Tränkwerkstoffe an Luft bei hohen Strömen. Z. Metallkd. 63 (1972) 651-654
  
−
Table 2.16: Application Examples and Forms of Supply for Silver and Silver Alloys
+
Althaus, B.; Vinaricky, E.: Das Abbrandverhalten verschieden hergestellter
 +
Wolfram-Kupfer-Verbundwerkstoffe im Hochstromlichtbogen.
 +
Metall 22 (1968) 697-701
  
−
===2.4.2.3 Silver-Palladium Alloys===
+
Gessinger, G.H.; Melton, K.N.: Burn-off Behaviour of WCu Contact Materials in an
−
The addition of 30 wt% Pd increases the mechanical properties as well as the
+
Electric Arc. Powder Metall. Int. 9 (1977) 67-72
−
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
+
Magnusson, M.: Abbrandverhalten und Rißbildung bei WCu-Tränkwerkstoffen
−
material transfer under DC loads (Table 2.19). On the other hand the electrical
+
unterschiedlicher Wolframteilchengröße. ETZ-A 98 (1977) 681-683
−
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
+
Heitzinger, F.; Kippenberg, H.; Saeger, K.E.; Schröder, K.H.: Contact Materials for
−
(>60V, >2A) as shown in Table 2.20. Because of the high palladium price these
+
Vacuum Switching Devices. Proc. XVth ISDEIV, Darmstadt 1992, 273-278
−
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
+
Grill, R.; Müller, F.: Verbundwerkstoffe auf Wolframbasis für
 +
Hochspannungsschaltgeräte. Metall 61 (2007) H. 6, 390-393
  
−
Fig. 2.67:
+
Slade, P.: G.: The Vacuum Interrupter- Theory; Design; and Application. CRC
−
Strain hardening
+
Press, Boca Raton, FL (USA), 2008
−
of AgPd30 by cold working
 
  
−
Fig. 2.68:
+
Frey, P.; Klink, N.; Saeger, K.E.: Untersuchungen zum Abreißstromverhalten von
−
Strain hardening
+
Kontaktwerkstoffen für Vakuumschütze. Metall 38 (1984) 647-651
−
of AgPd50 by cold working
 
  
−
Fig. 2.69:
+
Frey, P.; Klink, N.; Michal, R.; Saeger, K.E.: Metallurgical Aspects of Contact
−
Strain hardening
+
Materials for Vacuum Switching Devices. IEEE Trans. Plasma Sc. 17, (1989) 743-
−
of AgPd30Cu5
+
740
−
by cold working
 
  
−
Fig. 2.70:
+
Slade, P.: Advances in Material Development for High Power Vacuum Interrupter
−
Softening of AgPd30, AgPd50,
+
th Contacts. Proc.16 Int. Conf. on Electr. Contact Phenom.,
−
and AgPd30Cu5 after annealing of 1 hr
+
Loughborough 1992,1-10
−
after 80% cold working
 
  
−
Table 2.17: Physical Properties of Silver-Palladium Alloys
+
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
  
−
Table 2.18: Mechanical Properties of Silver-Palladium Alloys
+
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
  
−
Table 2.19: Contact and Switching Properties of Silver-Palladium Alloys
+
Kippenberg, H.: CrCu as a Contact Material for Vacuum Interrupters.
 +
th Proc.13 Int. Conf. on Electr. Contact Phenom. Lausanne 1986, 140-144
  
−
Table 2.20: Application Examples and Forms of Suppl for Silver-Palladium Alloys
+
Hauner, F.; Müller, R.; Tiefel, R.: CuCr für Vakuumschaltgeräte-
 +
Herstellungsverfahren, Eigenschaften und Anwendung.
 +
Metall 61 (2007) H. 6, 385-389
  
−
===2.4.3 Silver Composite Materials===
+
Manufacturing Equipment for Semi-Finished Materials
 +
(Bild)
  
−
===2.4.3.1 Silver-Nickel (SINIDUR) Materials===
+
[[de:Kontaktwerkstoffe_für_die_Elektrotechnik]]

Latest revision as of 12:54, 26 January 2023

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)
Figure 1: Powder-metallurgical manufacturing of composite materials (schematic) Ts = Melting point of the lower melting component)

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 (Bild)

Retrieved from "https://www.electrical-contacts-wiki.com/index.php?title=Contact_Materials_for_Electrical_Engineering&oldid=5513"