Cracking mechanisms in Ag-SnO2 contact materials and their role in the erosion process

The authors present the results of an investigation conducted into the factors governing the erosion of Ag-SnO/sub 2/ electric contact materials by repeated electric arcing and the manner in which these factors are altered by chemical effects. Two features found to have major influences were the inhomogeneous interfaces between the Ag matrix and the SnO/sub 2/ granules, and the wetting characteristics of the surface. The Ag/SnO/sub 2/ interfaces, which serve as paths for crack propagation, appear to have dominant influence during the earlier stages of erosion, while the extent of surface wetting by molten silver, which was found capable of altering the stress intensity at the crack tip, predominates in the later stages. The effect of dopant additives in altering the surface activity was also examined.>