Changes

<tr><th><p class="s12">Material</p></th><th><p class="s12">Micro Structure Condition</p></th><th><p class="s12">Vickers</p><p class="s12">Hardness HV 10</p></th><th><p class="s12">Tensile Strength</p><p class="s12">[MPa]</p></th></tr><tr><td><p class="s12">WolframTungsten</p></td><td><p class="s12">Lightly worked structure</p><p class="s12">(wire and strip &gt; 1.0 mm thick)</p><p class="s12">Strongly worked structure</p><p class="s12">(wire and strip &lt; 1.0 mm thick)</p><p class="s12">Re-crystallized structure</p></td><td><p class="s12">300 - 500</p><p class="s12">500 - 750</p><p class="s12">360</p></td><td><p class="s12">1000 - 1800</p><p class="s12">1500 - 5000</p><p class="s12">1000 - 1200</p></td></tr><tr><td><p class="s12">MolybdänMolybdenum</p></td><td><p class="s12">Lightly worked structure</p><p class="s12">(wire and strip &gt; 1.0 mm thick)</p><p class="s12">Strongly worked structure</p><p class="s12">(wire and strip &lt; 1.0 mm thick)</p><p class="s12">Re-crystallized structure</p></td><td><p class="s12">140 - 320</p><p class="s12">260 - 550</p><p class="s12">140 - 160</p></td><td><p class="s12">600 - 1100</p><p class="s12">800 - 2500</p><p class="s12">600 - 900</p></td></tr></table>

Ag/W contact materials combine the high electrical and thermal conductivity of silver with the high arc erosion resistance of the high melting tungsten metal (<xr id="tab:Physical Properties of-Contact Materials Basedon Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/><!--(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 (<xr id="fig:Micro structure of Ag W 25 75"/><!--(Fig. 2.134)-->, <xr id="fig:Micro structure of Ag WC 50 50"/><!--(Fig. 2.135)--> and <xr id="tab:Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/>).

During repeated switching under arcing loads, tungsten oxides and mixed oxides (silver tungstates – Ag₂ WO₄) are formed on the Ag/W surface, creating 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 or Ag/WC/C contact parts.

!Vickers<br/>Hardness<br/>[HV10HV5]

|48 47 - 5253|1312,0 9 - 13,49|960|3,85|45|2629 - 38|120 110 - 140175

|38 37 - 4243|1413,0 9 - 14,45|960|4,17|41|2421 - 32|140 150 - 160240

|33 32 - 3738|14,5 - 14,9|960|4,55|38|22|150 - 180|-|Ag/w 30/70 [[#text-reference|¹]]|28 - 32|15,0 - 15,4|960|5,0|34|20|160 - 190|-|Ag/W 25/75 [[#text-reference|¹]]|23 21 - 2731|15,5 - 15,8|960|5,26|33|19|170 160 - 200260

|Ag/W 2032/80 68 [[#text-reference|¹]]|18 29 - 2235|1514,8 3 - 1615,32|960|5,56|31|1821 - 30|180 - 230265

|58 57 - 6263|11,6 - 11,9|960|412,172|41|24|130 21 - 160|-|Ag/WC 50/50 [[#text-reference|¹]]|48 - 52|12,0 - 12,4|960|4,55|38|2229|140 - 170200

|38 37 - 4243|12,4 5 - 1213,83|960|4,76|36|2118 - 25|150 230 - 180340

|Ag/WC 35/65 [[#text-reference|¹]]|33 - 37|12,5 - 12,9|960|5,0|34|20|150 - 190|-|Ag/WC 8480/16C2 [[#text-reference|²]]

|9,8|960|2- 9,869|6030 - 38|35|- 55

|Ag/WC 7380/27C3 17C3 [[#text-reference|²]]|68 78 - 7282|9,6|960|41 - 9,768|3623 - 33|21|5035 - 55

|Ag/Mo 50WC 80/50 19C1 [[#text-reference|¹²]]|48 78 - 5282|9,9 5 - 10,2|960|5,0|34|2028 - 43|120 40 - 14060

|Ag/Mo 40WC 70/60 28C2 [[#text-reference|¹²]]|38 68 - 42 72|9,9 6 - 10,23|960|5,56|31|1824 - 32|130 35 - 17055

|Ag/Mo 3065/70 35 [[#text-reference|¹]]|28 62 - 3268|109,0 9 - 10,49|960|5,88|29|1716 - 28|140 - 180130

This group of contact materials contains typically 40-65 wt-% of the very hard and erosion wear resistant tungsten carbide and the high conductivity silver (<xr id="fig:Micro structure of Ag WC 50 50"/><!--(Fig. 2.135)--> and <xr id="tab:Physical Properties of-Contact Materials Basedon Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/><!--(Table 2.36)-->). Compared to Ag/W the Ag/WC materials exhibit a higher resistance against contact welding (<xr id="tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--(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 19 wt% WC and 3 1 wt% graphite or 16 wt% WC and 2 wt% graphite are manufactured using the single tip press-sinter-repress (PSR) process (<xr id="fig:Micro structure of -Ag WC 27 C3"/><!--(Fig. 2.136)-->).

Ag/Mo materials with typically 50-70 wt% molybdenum are usually produced by the powder metallurgical infiltration process (<xr id="fig:Micro structure of Ag Mo 35 65"/><!--(Fig. 2.137)--> and <xr id="tab:Physical Properties of-Contact Materials Basedon Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/><!--(Table 2.36)-->). Their contact properties are similar to those of Ag/W materials (<xr id="tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--(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 (<xr id="tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/><!--(Table 2.38)-->).

<tr><th><p class="s12">Material</p></th><th><p class="s12">Properties</p></th></tr><tr><td><p class="s12">Silver-Tungsten</p><p class="s12"></p><p class="s12">Silver-tungsten carbide</p></td><td><p class="s12">Tendency to weld at high make currents in symmetrical pairing,</p><p class="s12">Higher contact resistance and higher temperature rise over increased number of operations through tungsten oxide and tungstate formation, especially for Ag/W,</p><p class="s12">High welding tendency of closed contacts during short circuit,</p><p class="s12">Very high arc erosion resistance, poor arc moving properties, High hardness and low formability,</p><p class="s12">Easy to braze and weld through Ag enriched backing layer</p></td></tr><tr><td><p class="s12">Silver-Tungsten Carbide plus GrafitGraphite</p></td><td><p class="s12">Low contact resistance and low temperature rise through graphite addition,</p><p class="s12">Lower tendency to contact welding, Lower arc erosion resistance than Ag/WWC</p></td></tr><tr><td><p class="s12">Silver-Molybdenum</p><p class="s12"></p></td><td><p class="s12">Better contact resistance stability due to less stable surface layers,</p><p class="s12">Lower arc erosion resistance than Ag/W</p></td></tr></table>

Copper–tungsten materials with typically 50-85 wt% tungsten are produced by the infiltration process with the tungsten particle size selected according to the end application [[#figures4|(Figs. 5 – 86)]] <!--(Figs. 2.138 – 2.141)--> and (<xr id="tab:Physical properties of copper-tungsten materials"/><!--(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 60/40 [[#text-reference1|^F]]<br/>|58 57 - 6263

|160 150 - 200

|W/Cu 65/35 [[#text-reference1|^F]]

|W/Cu 70/30 [[#text-reference1|^F]]|68 - 72|13,9 - 14,4|1083|4,55 - 5,56|31 - 38|18 - 22|190 - 230|-|W/Cu 80/20 [[#text-reference1|^F]]|78 - 82|15,3 - 15,9|1083|5,0 - 6,25|28 - 34|16 - 20|240 - 280|-|W/Cu 60/40 [[#text-reference2|^G]]|58 - 62|12,9 - 13,3|1083|3,85 - 4,55|38 - 45|22 - 26|150 - 180|-|W/Cu 65/35 [[#text-reference2|^G]]|63 - 67|13,6 - 14,0|1083|4,17 - 5,0|34 - 41|20 - 24|160 - 190|-|W/Cu 70/30 [[#text-reference2|^G]]

|160 - 195230

|W/Cu 75/25 [[#text-reference2|^G]]

|W/Cu 80/20 [[#text-reference2|^G]]

|180 - 210|-|W/Cu 70/30 [[#text-reference3|^H]]|68 - 72|13,9 - 14,4|1083|3,85 - 5,56|31 - 38|18 - 22 |180 - 210|-|W/Cu 75/25 [[#text-reference3|^H]]|73 - 77|14,6 - 15,2|1083|4,76 - 5,88|29 - 36|17 - 21|190 - 220|-|W/Cu 80/20 [[#text-reference3|^H]]|78 - 82|15,3 - 15,9|1083|5,0 - 6,25|28 - 34|16 - 20|200 - 240|-|W/Cu 85/15 [[#text-reference3|^H]]|83 - 87|15,8 - 16,5|1083|5,0 - 6,67|26 - 34|15 - 20|210 - 250280

W/Cu materials exhibit a very high arc erosion resistance (<xr id="tab:Contact and Switching Properties of Copper–Tungsten (CUWODUR) Contact Materials"/><!--(Table 2.40)-->). Compared to silver–tungsten materials, they are however less suitable to carry permanent current.

The main application areas for W/Cu 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 (<xr id="tab:Application Examples and Forms of Supply for Tungsten– Copper (CUWODUR) Contact Materials"/><!--(Table 2.41)-->). <figtable id="tab:Physical Properties of Copper Tungsten CUWODUR Contact Materials">[[File:Physical Properties of Copper Tungsten CUWODUR Contact Materials.jpg|right|thumb|Physical Properties of Copper Tungsten Contact Materials]]</figtable> 

[[File:Micro structure of W Cu 70 30 G.jpg|left|thumb|<caption>Micro structure of W/Cu 70/30 G</caption>]]</figure> <figure id="fig:Micro structure of W Cu 70 30 H">[[File:Micro structure of W Cu 70 30 H.jpg|left|thumb|<caption>Micro structure of W/Cu 70/30 H(coarse)</caption>]]

[[File:Micro structure of W Cu 70 30 F.jpg|left|thumb|<caption>Micro structure of W/Cu 70/30 F(fine)</caption>]]