Main Articel: [[Silver Based Materials| Silver Based Materials]]
==Silver Composite Materials==
===Silver-Nickel (SINIDUR) Materials===
Since silver and nickel are not soluble in each other in solid form and in the liquid
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
of these materials ''(Tables 2.21 and 2.22)''. The typical application of Ag/Ni
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
wt% Ni. The most widely used materials SINIDUR 10 and SINIDUR 20- and also
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
relays, wiring devices, appliance switches, thermostatic controls, auxiliary
switches, and small contactors with nominal currents >20A ''(Table 2.24)''.
Table 2.21: Physical Properties of Silver-Nickel (SINIDUR) Materials
Table 2.22: Mechanical Properties of Silver-Nickel (SINIDUR) Materials
Fig. 2.71:
Strain hardening
of Ag/Ni 90/10 by cold working
Fig. 2.72:
Softening of Ag/Ni 90/10
after annealing
for 1 hr after 80% cold working
Fig. 2.73:
Strain hardening
of Ag/Ni 80/20 by cold working
Fig. 2.74:
Softening of Ag/Ni 80/20
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
b) parallel to the extrusion direction
Fig. 2.76: Micro structure of Ag/Ni 80/20 a) perpendicular to the extrusion direction
b) parallel t o the extrusion direction
Table 2.23: Contact and Switching Properties of Silver-Nickel (SINIDUR) Materials
Table 2.24: Application Examples and Forms of Supply
for Silver-Nickel (SINIDUR) Materials
=== Silver-Metal Oxide Materials Ag/CdO, Ag/SnO<sub>2</sub>, Ag/ZnO===
The family of silver-metal oxide contact materials includes the material groups:
silver-cadmium oxide (DODURIT CdO), silver-tin oxide (SISTADOX), and silverzinc
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
Silver-cadmium oxide (DODURIT CdO) materials with 10-15 wt% are produced
by both, internal oxidation and powder metallurgical methods ''(Table 2.25)''.
The manufacturing of strips and wires by internal oxidation starts with a molten
alloy of silver and cadmium. During a heat treatment below it's melting point in a
oxygen rich atmosphere in such a homogeneous alloy the oxygen diffuses from
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
processes vary depending on the type of semi-finished material.
For Ag/CdO wires a complete oxidation of the AgCd wire is performed, followed
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
processes are typically converted by pressing, sintering and extrusion to wires
and strips. The high degree of deformation during hot extrusion produces a
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
Press-Sinter-Repress process (PSR) offers economical advantages. The
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
starting materials can help influence certain contact properties for specialized
applications.
Fig. 2.77:
Strain hardening of internally oxidized
Ag/CdO 90/10 by cold working
Fig. 2.78:
Softening of internally oxidized
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
Forms of Supply of Extruded Silver Cadmium Oxide
(DODURIT CdO) Contact Materials
Fig. 2.79:
Strain hardening of
Ag/CdO 90/10 P by cold working
Fig. 2.80: Softening
of Ag/CdO 90/10 P after annealing
for 1 hr after 40% cold working
Fig. 2.81:
Strain hardening
of Ag/CdO 88/12 WP
Fig. 2.82:
Softening of Ag/CdO 88/12WP after annealing
for 1 hr after different degrees of
cold working
Fig. 2.83: Micro structure of Ag/CdO 90/10 i.o. a) close to surface
b) in center area
Fig. 2.84: Micro structure of Ag/CdO 90/10 P:
a) perpendicular to extrusion direction
b) parallel to extrusion direction
Fig. 2.85:
Micro structure of Ag/CdO 90/10 ZH:
1) Ag/CdO layer
2) AgCd backing layer
Fig. 2.86: Micro structure of AgCdO 88/12 WP: a) perpendicular to extrusion direction
b) parallel to extrusion direction
*Silver–tin oxide(SISTADOX)materials
Over the past years, many Ag/CdO contact materials have been replaced by
Ag/SnO<sub>2</sub> based materials with 2-14 wt% SnO<sub>2</sub> because of the toxicity of
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
during heat treatment of alloys containing > 5 wt% of tin in oxygen, dense oxide
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>
contact materials. Besides SnO<sub>2</sub> a smaller amount (<1 wt%) of one or more
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
additives improve the wettability of the oxide particles and increase the viscosity
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
which provide specific advantages of the resulting materials in respect to their
contact properties ''(Figs. 2.87 – 2.119)''. Some of them are described here as
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.
:'''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.
:'''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.
:'''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>.
Further processing of these differently produced powders follows the
conventional processes of pressing, sintering and hot extrusion to wires and
strips. From these contact parts such as contact rivets and tips are
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:
Strain hardening of
Ag/SnO<sub>2</sub> 92/8 PE by cold working
Fig. 2.88:
Softening of
Ag/SnO<sub>2</sub> 92/8 PE after annealing
for 1 hr after 40% cold working
Table 2.26: Physical and Mechanical Properties as well as Manufacturing Processes and
Forms of Supply of Extruded Silver-Tin Oxide (SISTADOX) Contact Materials
Fig. 2.89:
Strain hardening of
Ag/SnO<sub>2</sub> 88/12 PE by cold working
Fig. 2.90:
Softening of Ag/SnO<sub>2</sub> 88/12 PE
after annealing for
1 hr after 40% cold working
Fig. 2.91:
Strain hardening of oxidized
Ag/SnO<sub>2</sub> 88/12 PW4 by cold working
Fig. 2.92:
Softening of Ag/SnO<sub>2</sub> 88/12 PW4 after
annealing for 1 hr
after 30% cold working
Fig. 2.93:
Strain hardening of
Ag/SnO<sub>2</sub> 98/2 PX
by cold working
Fig. 2.94:
Softening of
Ag/SnO<sub>2</sub> 98/2 PX
after annealing
for 1 hr after 80%
cold working
Fig 2.95:
Strain hardening
of Ag/SnO<sub>2</sub> 92/8 PX
by cold working
Fig. 2.96:
Softening of
Ag/SnO<sub>2</sub> 92/8 PX
after annealing for 1 hr
after 40% cold working
Fig. 2.97:
Strain hardening of internally
oxidized
Ag/SnO<sub>2</sub> 88/12 TOS F
by cold working
Fig. 2.98:
Softening of
Ag/SnO<sub>2</sub> 88/12 TOS F after
annealing for 1 hr after 30%
cold working
Fig. 2.99:
Strain hardening of
internally oxidized
Ag/SnO<sub>2</sub> 88/12P
by cold working
Fig. 2.100:
Softening of
Ag/SnO<sub>2</sub> 88/12P
after annealing for 1 hr after
40% cold working
Fig. 2.101:
Strain hardening of
Ag/SnO<sub>2</sub> 88/12 WPC
by cold working
Fig. 2.102:
Softening of Ag/SnO<sub>2</sub> 88/12 WPC after annealing
for 1 hr after different degrees of cold working
Fig. 2.103:
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
====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)
==Tungsten and Molybdenum Based Materials==
