Titanium-Tungsten Carbide/Silver: A New Electric Contact Material

The performance of a new contact material (Ti,W)C-Ag, has been evaluated. Two compositions of this contact, 50 percent by weight Ag and 35 percent by weight Ag, haye been Used. The former contact showed good performance under switching duty (20 A, 110 V, 99 percent power factor). The latter contact had insufficient Ag, however, to maintain a low contact resistance throughout the switching experiments. Both contact structures showed excellent resistance to arc erosion under short circuit conditions. Microchemical (EDAX, EMA, DIMA), metallographic, and X-ray diffraction techniques have been used to analyze the chemical and micr0structural factors. These have been used to explain the good electrical contact characteristics. Gravimetric oxidation tests have also been conducted to characterize the new contacts. Several factors have been identified that contribute to the improved contact material: a) good wetting of (Ti,W)C with silver; b) higher oxidation resistance of (Ti,W)C; c) wide stability range of the mixed Ti-W carbide phase; d) formation of oxygen solid solutions and/or suboxides of titanium; and e) the generation of a CO/CO2 gas blanket during oxidation. This new contact material is shown to be a significani addition to the family of materials used for electric contact applications.