Effects of high oxygen-affinity elements on microstructure of Cu-Cr alloy ingots

Cu-Cr alloys with additions of high oxygen affinity elements C, Al, La, Ti and Zr were inductively melted and cast in an alumina crucible. Microstructure of the as-cast ingots was investigated using an optical microscope and a scanning electron microscope. The ingots with low Cr contents solidify into a dendritic microstructure, whereas those with high Cr content solidify into a droplet-shaped microstructure due to the occurrence of liquid phase separation before solidification. The additions of these elements reduce the amount of oxide inclusions generally, and alter the morphology of the oxide inclusions as well. However, they produced different effects on the liquid miscibility gap of high Cr alloys. The additions of Al, Ti and La tend to reduce the miscibility gap, whereas the addition of C tends to broaden the miscibility gap. These changes in the microstructure were discussed with respect to the performance of the Cu-Cr contact material.