Author:

Abstract:

WC-Ag and W-Ag refractory electrical contacts belong to one of the most important contact material families used in state-of-the-art circuit breakers which operate at a wide range of currents (10-630-6300 A) in air depending on their application. During a short circuit or overload (5-250 kA), the contact must “open” to protect the remaining circuit. Consequently, an arc is generated which is fuelled by the plasma generated from ionization of molecules in air which reaches temperatures close to 20000°C. The superior thermal and electrical conductivity of silver combined with adequate mechanical and arc erosion resistance of a refractory carbide, makes it the ideal material for usage under severe arcing conditions. The hard WC particles suspended in the soft Ag matrix inhibits the contacts to weld together at such high temperatures. In the present study, spark plasma sintering is explored as a new densification route and compared with the conventional densification process by infiltration of silver in a porous network of WC. SPS proved to be an interesting alternative technology to produce fully dense Ag-WC composites with a significantly refined microstructure. Break-only test, which simulate arcing conditions in real switching devices, were carried out to investigate the microstructure after switching. The effect of the WC particle size and amount of Ag on the Vickers hardness was also studied.