Cracking mechanisms in Ag-SnO/sub 2/ contact materials and their role in the erosion process

An investigation has been 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 influence 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 be the 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.<
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