Metallurgical study of Ag-Cd and Ag-CdO alloy electrical contacts

Ag-Cd and Ag-CdO contacts, made both by sintering and postoxidation, were evaluated as to their durability by inductive and capacitive overcurrent tests according to the IEC 328 and NBR 6269 standards. Materials transfer during electric tests were monitored at 10000, 20000, 30000, and 40000 switching operations by scanning electron microscopy (SEM), energy-dispersive X-ray analysis, and chemical analysis. Better performance with regard to erosion was found for Ag-CdO postoxidized contacts, compared with sintered ones. Structural changes on the surface of Ag-Cd and Ag-CdO contacts were studied by SEM. The surface of Ag-Cd contacts changed rather uniformly, while Ag-CdO contacts developed considerable inhomogeneity. Sintered and postoxidized contacts also have also different structures. Sintered Ag-CdO contacts show a matrix with pulverized droplets while postoxidized Ag-CdO show very little change.<
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