Microstructural evolutions induced by an electrical breakdown in a binary Cu-25Cr alloy

Abstract

Cu-Cr based alloys with a high Cr content are widely used as electrical contact materials in vacuum interrupters due to their good combination of electrical, thermal, and mechanical properties. During a current interruption process in a vacuum, the establishment of an electrical arc results in a severe local thermal input onto the contact material surface. Few studies have closely investigated the microstructural evolution during this phenomenon as well as the Cu-Cr alloy properties evolution. This study reports the microstructural, electrical conductivity, and hardness evolution of a Cu-25Cr (25 wt%Cr) solid state sintered alloy as electrical contact before and after successive current interruptions. Electron scanning and optical microscopy show that this microstructural evolution is a result of a complex phenomenon. Local and heterogeneous thermal conditions take place resulting in significant microstructural evolution. The resulting microstructure is related to out-of-equilibrium solidification conditions. Electrical conductivity is decreased by half in the whole thermally affected zone by the electrical arc and hardness is multiplied by three to four times.