Abstract
The sintering behaviour of Cu-25 wt-%Cr contact materials produced by powder metallurgy is investigated with respect to the processing variables, such as oxygen content, sintering temperature, time, stearate additives and microstructural features. The sintering temperature of the mixture is determined from the temperature of the liquid phase formation by differential thermal analysis (DTA). Properties of sintered products prepared with and without the reduction treatment of chromium powders are compared in terms of sintered density and electrical conductivity. The initial oxygen content of the chromium powders is decreased from 4500 ppm to 200 ppm by a new method of reduction treatment developed previously and it is observed that the sintered density is increased from 95% theoretical density to 98% theoretical density while the corresponding electrical conductivity increased from 28% IACS to 39% IACS (International Annealed Copper Standard). The sintered density further increased to 99% theoretical density with an electrical conductivity level of 45% IACS by the addition of 0·5 wt-% lithium stearate to the Cu-25 wt-%Cr (200 ppm O2) mixture. By cold working and age hardening, the electrical conductivity is increased to 55% IACS with accomplishing a hardness value of 154 HV5 in the 50% cold worked samples.
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