Redistribution of SnO₂ particles in Ag/SnO₂ materials during rapid solidification

Melt spinning experiments were performed on Ag-12 wt.% SnO₂ contact materials with and without CuO addition for the purpose of simulating the rapid solidification process of an instantaneously remelted thin surface layer during arcing. The microstructure of the rapidly solidified ribbons was investigated using optical and scanning electron microscopy, and compared with that of the samples subjected to arcing tests. The results evidenced a redistribution of the reinforcement SnO₂ particles during rapid solidification as well as a strong dependence of it on the addition of a small amount of CuO to the starting materials. In CuO-free ribbons, much more of the SnO₂ particles were confined at grain boundaries rather than engulfed in Ag matrix grains. In CuO-doped ribbons, however, the SnO₂ particles were uniformly distributed both inside Ag-matrix grains and at grain boundaries. Additionally, short SnO₂ rods were formed on the surfaces of the CuO-doped ribbons. Similar effects of the addition of CuO were noted for arc-tested samples. The results were discussed with respect to several models dealing with the particle-dendrite interaction during solidification.