Metallurgical study of CuCr contact surface in breakdown

The correlation between conditioning and surface morphological change in cathode and anode electrodes was studied using CuCr alloy contacts. In the cathode test, on the early stage of conditioning, many small craters caused by breakdown were observed on the Cr particles of the cathode electrode, together with small sputter particles mainly composed of Cu. On the next stage, large craters were developed on the Cu matrix in addition to the small craters on the Cr particles, and sputter particles composed of Cu and Cr increased. On the final stage, broad molten areas surrounded with a sputter-covered and non-molten region were formed. In the anode test, pits and tracks were first formed preferentially on Cu/Cr interfaces and scratches. The broad area including both Cu matrix and Cr particles next melted at the center of the contact, and this molten area merely enlarged until the completion of conditioning. The surface morphological change in the cathode electrode well corresponded to the conditioning process in dc breakdown. 6 refs., 6 figs.