CuW composites are used where the combination of high heat resistance, high electrical and thermal conductivity, and low thermal expansion are needed. Some of the applications are in
electric resistance welding, as
electrical contacts, and as
heat sinks. As contact material, the composite is resistant to erosion by electric arc. WCu alloys are also used in electrodes for
electrical discharge machining and
electrochemical machining. The CuW75 composite, with 75% tungsten, is widely used in
chip carriers, substrates, flanges, and frames for
power semiconductor devices. The high thermal conductivity of copper together with the low thermal expansion of tungsten allows thermal expansion matching to
silicon,
gallium arsenide, and some
ceramics. Other materials for this applications are copper-molybdenum alloy,
AlSiC, and
Dymalloy. Composites with 70–90% of tungsten are used in liners of some specialty
shaped charges. The penetration is enhanced by factor 1.3 against copper for homogeneous steel target, as both the density and the break-up time are increased. Tungsten powder based shaped charge liners are especially suitable for
oil well completion. Other ductile metals can be used as a binder in place of copper as well.
Graphite can be added as lubricant to the powder. CuW can also be used as a contact material in a vacuum. When the contact is very fine grained (VFG), the electrical conductivity is much higher than a normal piece of copper tungsten. Copper tungsten is a good choice for a vacuum contact due to its low cost, resistance to arc erosion, good conductivity, and resistance to mechanical wear and contact welding. CuW is usually a contact for vacuum, oil, and gas systems. It is not a good contact for air since the surface will oxidize when exposed. CuW is less likely to erode in air when the concentration of copper is higher in the material. The uses of CuW in the air are as an arc tip, arc plate, and an arc runner. Copper tungsten materials are often used for arcing contacts in medium to high voltage
sulfur hexafluoride (SF6) circuit breakers in environments that can reach temperatures above 20,000K. The copper tungsten material's resistance to arc erosion can be increased by modifying the grain size and chemical composition. == Properties ==