The effects of Te and misch metal additions on the microstructure and properties of rapidly solidified Ag-Sn-In alloy for electrical contact applications

Abstract

High wear resistance with a stable contact resistance is a prerequisite Im electrical contact applications. Although Ag-CdO has been widely used as an electrical contact material, there are intrinsic problems of forming large Cd oxide particles and environmental regulations against using Cd. Newly developed Ag-SnO2 alloys are considered good candidates to replace Ag-CdO alloys due to their stable and fine oxide formation capabilities. In addition, further improvements in performance are expected in Ag-SnO2 alloys by alloy modification and/or solidification processing to produce finer and stable oxide dispersions through internal oxidation. The effect of the addition of Te and misch metal, which function as oxide forming elements, on Ag-Sn-In ternary alloy was investigated. Up to 0.5 wt.% of Te and misch metals were added and rapidly solidified to maximize their effect on fine oxide formation in an Ag matrix. Resulting microstructrual changes and properties were evaluated through electron microscopy, spectroscopy, and hardness measurements. The role of Te addition was to provide nucleation sites for complex oxides such as In2TeO6 phase and to ensure fine and well dispersed SnO2 oxide particles. A rapid increase in size was observed for both grain and oxide particles when Te content exceeded 0.3 wt.%. Misch metal addition, on the other hand, had a pronounced effect on grain size reduction of the Ag matrix, and was interpreted as a consequence of decreasing the latent heat of solidification. Maximum hardness was achieved at 0.3 wt.% misch metal addition. In both cases, hardness decreased rapidly at 0.5 wt.% addition and was attributed to the large grain size of the matrix, and also large oxide particles aggregated in the matrix grains.