Tungsten is characterized by its advantageous properties of high melting and boiling points, sufficient electrical and thermal conductivity and high hardness and density ''(<xr id="tab:Mechanical_Properties_of_Tungsten_and_Molybdenum"/><!--(Table 2.35)''-->). It is mainly used in the form of brazed contact tips for switching duties , that require a rapid switching sequence , such as horn contacts for cars and trucks.

<figtable id="tab:Mechanical_Properties_of_Tungsten_and_Molybdenum"><caption>'''<!--Table 2.35: -->Mechanical Properties of Tungsten and Molybdenum'''</caption><table border="1" cellspacingclass="0" style="border-collapse:collapsetwocolortable"><tr><tdth><p class="s12">Material</p></tdth><tdth><p class="s12">Micro Structure Condition</p></tdth><tdth><p class="s12">Vickers</p><p class="s12">Hardness HV 10</p></tdth><tdth><p class="s12">Tensile Strength</p><p class="s12">[MPa]</p></tdth></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></figtable>

=== Silver–Tungsten (SIWODUR) Materials===Ag/W (SIWODUR) contact materials combine the high electrical and thermal conductivity of silver with the high arc erosion resistance of the high meltingtungsten metal ''(<xr id="tab:Physical Properties of Contact Materials Based on 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 ofliquid phase sintering or by infiltration. Particle size and shape of the starting powders are determining the micro structure and the contact specific properties of this material group ''(Figs<xr id="fig:Micro structure of Ag W 25 75"/><!--(Fig. 2.134 and )-->, <xr id="fig:Micro structure of Ag WC 50 50"/><!--(Fig. 2.135) (Table 2.37--> 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 2 4 poorly conducting layers which increase the contact resistance and by this the temperature rise during current carrying. Because of this fact the Ag/W is paired in many applications with Ag/C or Ag/WC/C contact parts.

switches and industrial circuit breakers ''(<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)''-->). In north and south america they are also used in large volumes in miniature circuit breakers of small to medium current ratings in domestic wiring as well as for commercial power distribution.

<figtable id=== Silver–Tungsten Carbide (SIWODUR C) "tab:Physical Properties of Contact Materials===This group of contact materials contains the typically 40Based on Silver-65 wtTungsten, Silver-% of the very hard Tungsten Carbide and erosion wear resistant tungsten carbide and the high conductivity silver Silver Molybdenum"><caption>'''(Fig. 2.135) (<!--Table 2.36)'7:-->Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum'. Compared to Ag/W the Ag/WC (SIWODUR C) materials exhibit a higher resistance against contact welding ''(Table 2.37)''. The rise in contact resistance experienced with Ag</W is less pronounced in Ag/WC because during arcing a protective gas layer of CO is formed which limits the reaction of oxygen on the contact surface and therefore the formation of metal oxides.caption>

Higher requirements on low temperature rise can be fulfilled by adding a small amount of graphite which however increases the arc erosion. Silver–tungsten{| class="twocolortable" style="text-align: left; font-size: 12px"|-!Materialcarbide–graphite materials with for example 27 !Silver<br/>Content<br/>[wt.% ]!Density<br/>[g/cm³]!Electrical<br/>Conductivity<br/>[MS/m]!Vickers<br/>Hardness<br/>[HV5]|-|Ag/W 50/50 [[#text-reference|¹]]<br/>|47 - 53|12,9 - 13,9|29 - 38|110 - 175|-|Ag/W 40/60 [[#text-reference|¹]]|37 - 43|13,9 - 14,5|21 - 32|150 - 240|-|Ag/W 35/65 [[#text-reference|¹]]|32 - 38|14,1 - 15,1|21 - 31|160 - 260|-|Ag/W 32/68 [[#text-reference|¹]]|29 - 35|14,3 - 15,2|21 - 30|180 - 265|-|Ag/WC and 60/40 [[#text-reference|¹]]|57 - 63|11,6 - 12,2|21 - 29|140 - 200|-|Ag/WC 40/60 [[#text-reference|¹]]|37 - 43|12,5 - 13,3 wt% graphite or |18 - 25|230 - 340|-|Ag/WC 80/16C2 [[#text-reference|²]]|80 - 84|9,2 - 9,9|30 - 38|35 - 55|-|Ag/WC 80/17C3 [[#text-reference|²]]|78 - 82|9,1 - 9,8|23 - 33|35 - 55|-|Ag/WC 80/19C1 [[#text-reference|²]]|78 - 82|9,5 - 10,5|28 - 43|40 - 60|-|Ag/WC 70/28C2 [[#text-reference|²]]|68 - 72|9,6 - 10,3|24 - 32|35 - 55|-|Ag/Mo 65/35 [[#text-reference|¹]]|62 - 68|9,9 - 10,9|16 wt% WC and - 28|140 - 130|-|}<div id="text-reference">₁manufactured by infiltration</div><div id="text-reference">_{2 wt% graphite are} manufactured using the single tip by press-sinter-repress (PSR) process ''(Fig. 2.136)''.</div></figtable>

The applications === Silver–Tungsten Carbide Materials===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 AgWC 50 50"/><!--(Fig. 2.135)--> and <xr id="tab:Physical Properties of Contact Materials Based on Silver-Tungsten, Silver-Tungsten Carbide and Silver Molybdenum"/WC contacts are similar ><!--(Table 2.36)-->). Compared to those for 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 2.3837)-->)''. 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.

=== Silver–Molybdenum (SILMODUR) Materials===Ag/Mo 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 typically 50-70 for example 19 wt% WC and 1 wt% graphite or 16 wt% WC and 2 wt% molybdenum graphite are usually produced by manufactured using the powder metallurgical infiltration process ''single tip press-sinter-repress (Fig. 2.137PSR) process (Table 2.36)''. Their contact properties are similar to those <xr id="fig:Micro structure of -AgWC 27 C3"/W materials ''><!--(Table Fig. 2.37136)''. Since the molybdenum oxide is thermally less stable than tungsten oxide the self-cleaning effect of Ag/Mo contact surface during arcing is more pronounced and the contact resistance remains lower than that of Ag/W. The arc erosion resistance of Ag/Mo however is lower than the one for Ag/W materials. The main applications for Ag/Mo contacts are in equipment protecting switching devices ''(Table 2.38->)''.

Fig. 2.134: Micro structure The applications of Ag/WC contacts are similar to those for Ag/W 25(<xr id="tab:Contact and Switching Properties of Contact Materials Based on Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"/75><!--(Table 2.38)-->).

=== Silver–Molybdenum Materials===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. 2.135137)--> and <xr id="tab:Physical Properties of Contact Materials Based on 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: Micro structure 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/WC 50Mo 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)"/50><!--(Table 2.38)-->).

'''Table 2.36<figtable id="tab: Physical Contact and Switching Properties of Contact Materials Based on Silver–Tungsten Silver – Tungsten (SIWODUR),Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)"><caption>'''<!--Table 2.37:-->Contact and Switching Properties of Contact Materials Based on Silver – Tungsten, Silver–Tungsten Carbide and Silver Molybdenum'''</caption><table class="twocolortable"><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 Graphite</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/WC</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></figtable>

[[File<figtable id="tab:Physical Properties of-Contact Materials Based.jpg|right|thumb|Physical and Switching Properties of Contact Materials Based on Silver–Tungsten Silver – Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)]]"><caption>'''<!--Table 2.38:-->Contact and Switching Properties of Contact Materials Based on Silver – Tungsten, Silver–Tungsten Carbide and Silver Molybdenum'''</caption>

'''Table 2.37{| class="twocolortable" style="text-align: Contact and Switching Properties left; font-size: 12px"|-!Material !Application Examples!Form of Contact Materials Based on Silver – TungstenSupply|-|Ag/W<br />|Circuit breakers (SIWODURnot current limiting)|rowspan="3" | Contact tips, Silver–Tungsten Carbide brazed and welded<br />contact parts|-|Ag/W<br /><br />Ag/WC<br /><br />Ag/WC/C<br /> |(SIWODUR Main) Power switches<br /> paired with Ag/C) and Silver Molybdenum <br />Fault current circuit breakers<br />(SILMODURpaired with Ag/C)'''|-|Ag/Mo<br />|Device protection switches|}</figtable>

<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p classCopper–Tungsten Materials="s12">Material/ DODUCO- Designation</p></td><td><p class="s12">Properties</p></td></tr><tr><td><p class="s12">Silver-Tungsten</p><p class="s12">SIWODUR</p><p class="s12">SilverCopper–tungsten materials with typically 50-85 wt% tungsten are produced by the infiltration process with the tungsten carbide SIWODUR C</p></td><td><p class="s12">Tendency particle size selected according to weld at high make currents in symmetrical pairing,the end application [[#figures4|(Figs. 5 – 6)]] </p!--(Figs. 2.138 – 2.141)-->and (<p classxr id="s12">Higher contact resistance and higher temperature rise over increased number tab:Physical properties of operations through copper-tungsten oxide and tungstate formation, especially for Ag/W,</p><p class="s12materials">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!--(Table 2.39)-Tungsten Carbide plus Grafit SIWODUR C Plus</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/W</p></td></tr><tr><td><p class="s12">Silver-Molybdenum</p>). To increase the wettability of the tungsten skeleton by copper a small amount of nickel <p class="s12">SILMODUR</p></td><td><p class="s12">Better contact resistance stability due 1 wt% is added to less stable surface layers,</p><p class="s12">Lower arc erosion resistance than Ag/W</p></td></tr></table>the starting powder mix.

<figtable id="tab:Physical properties of copper-tungsten materials"><caption>'''Table 2.38: Application Examples and Forms Physical properties of Supply for Contact Materials Basedon Silver–Tungsten (SIWODUR), Silver–Tungsten Carbide (SIWODUR C) and Silver Molybdenum (SILMODUR)copper-tungsten materials'''</caption>

{| class="twocolortable" style== Copper–Tungsten (CUWODUR) Materials==="text-align: left; font-size: 12px"Copper–tungsten (CUWODUR) materials with typically 50|-85 !Material!Tungsten<br/>Content<br/>[wt.% tungsten are produced by the infiltration process with the tungsten particle size selected]!Density<br/>[g/cm³]!Melting Point<br/>[°C]!Electrical<br/>Resistivity<br/>[µΩ*cm]!Electrical<br/>Conductivity<br/>[% IACS]!Electrical<br/>Conductivity<br/>[MS/m]!Vickers<br/>Hardness<br/>[HV10]|-|W/Cu 60/40 <br/>|57 - 63|12,9 - 13,3|1083|3,85 - 4,55|38 - 45|22 - 26|150 - 200|-|W/Cu 65/35|63 - 67|13,6 - 14,0|1083|4,17 - 5,0|34 - 41|20 - 24|160 - 210|-|W/Cu 70/30 |68 - 72|13,9 - 14,4|1083|3,85 - 5,56|31 - 38|18 - 22|160 - 230|-|W/Cu 75/25 |73 - 77according to the end application ''(Figs. |14,6 - 15,2.138 – 2.141) (Table 2.39)''. To increase the wettability of the tungsten skeleton by copper a small amount of nickel |1083|4,76 - 5,88|29 - 36|17 - 21|180 - 210|-|W/Cu 80/20|78 - 82|15,3 - 15,9|1083|5,0 - 6,25|28 - 34|16 - 20|180 - 280|-|}< 1 wt% is added to the starting powder mix./figtable>

W/Cu materials exhibit a very high arc erosion resistance ''(Table 2.40)''. Compared to silver–tungsten materials , they are however less suitable to carrypermanent current.

With a solid tungsten skeleton , as it is the case for W/C infiltrated materials with 70-85 wt% tungsten , the lower melting component copper melts and vaporizes in the intense electrical arc. At the boiling point of copper (2567°C) , the still solid tungsten is efficiently “cooled” and remains pretty much unchanged.

During very high thermal stress on the W/Cu contacts, for example during short circuit currents > 40 kA , the tungsten skeleton requires special high mechanical strength. For such applications , a high temperature sintering of tungsten from selected particle size powder is applied before the usual infiltration with copper (example: CUWODUR H).

For high voltage load switches , the most advantageous contact system consists of a contact tulip and a contact rod. Both contact assemblies are usually made usually from the mechanically strong and high conductive CuCrZr material and W/Cu as the arcing tips. The thermally and mechanically highly stressed attachment between the two components is often achieved by utilizing electron beam welding or capacitor discharge percussion welding. Other attachment methods include brazing and cast-on of copper , followed by cold forming steps to increase hardness and strength.

The main application areas for CUWODUR W/Cu materials are as arcing contacts in load and high power switching , in medium and high voltage switchgear as wellas electrodes for spark gaps and over voltage arresters ''(Table 2.41)''.

'''Table 2<div class="multiple-images"><figure id="fig:Micro structure of W Cu 70 30 G"> [[File:Micro structure of W Cu 70 30 G.39: Physical Properties jpg|left|thumb|<caption>Micro structure of Copper–Tungsten W/Cu 70/30 (CUWODURcoarse) Contact Materials'''</caption>]]</figure>

<figure id="fig:Micro structure of W Cu 70 30 F">[[File:Physical Properties Micro structure of Copper Tungsten CUWODUR Contact MaterialsW Cu 70 30 F.jpg|rightleft|thumb|Physical Properties <caption>Micro structure of Copper Tungsten W/Cu 70/30 (CUWODURfine) Contact Materials</caption>]]</figure>

Fig. 2.139: Micro structure of W/Cu 70/30 G Fig. 2.140: Micro structure of W/Cu 70/30 H Fig. 2.138: Micro structure of W/Cu 70/30 F Fig. 2.141: Micro structure of W/Cu 80/20 H [[File:Micro structure of2.jpg|right|thumb|Micro structure of W/Cu 70/30 G, W/Cu 70/30 H, W/Cu 70/30 F, W/Cu 80/20 H]] '''Table 2.40:''' Contact and Switching Properties of Copper–Tungsten (CUWODUR) Contact Materials<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s12">Material/ DODUCO- Designation</p></td><td><p class="s12">Properties</p></td></tr><tr><td><p class="s12">W/Cu F</p><p class="s12">CUWODUR F</p></td><td><p class="s12">Very high arc erosion resistance,</p><p class="s12">Uniform erosion pattern after high operation frequency, Very high mechanical strength,</p><p class="s12">Highly resistant against thermal and mechanical shock</p></td></tr><tr><td><p class="s12">W/Cu G</p><p class="s12">CUWODUR G</p></td><td><p class="s12">Very high arc erosion resistance, Very high mechanical strength,</p><p class="s12">Highly resistant against thermal and mechanical shock.</p></td></tr><tr><td><p class="s12">W/Cu H</p><p class="s12">CUWODUR H</p></td><td><p class="s12">Very high arc erosion resistance, very high mechanical strength, Especially high resistance against thermal and mechanical shock.</p></td></tr></tablediv> '''Table 2.41:''' Application Examples and Forms of Supply for Tungsten– Copper (CUWODUR) Contact Materials<table border="1" cellspacing="0" style="border-collapse:collapse"><tr><td><p class="s12">Material</p></td><td><p class="s12">Application Examples</p></td><td><p class="s12">Form of Supply</p></td></tr><tr><td><p class="s12">W/Cu F</p></td><td><p class="s12">Transformer tap changers,</p><p class="s12">Medium voltage circuit breakers</p></td><td><p class="s12">Contact tips, formed parts, brazed</p><p class="s12">and welded contact parts</p></td></tr><tr><td><p class="s12">W/Cu G</p></td><td><p class="s12">Overvoltage arresters with spark gap,</p><p class="s12">Medium voltage circuit breakers, Medium voltage power switches, High voltage power switches and circuit breakers</p></td><td><p div class="s12clear">Contact tips, formed parts, brazed</p><p class="s12">and welded contact parts; Contact tulips, rods and tubes</p></td></tr><tr><td><p class="s12">W/Cu H</p></td><td><p class="s12">High voltage power switches and circuit</p><p class="s12">breakers for very high short circuit currents</p></td><td><p class="s12">Welded contact parts; Contact tulips,</p><p class="s12">rods</p></td></tr></tablediv>