| Summary: In this study, AgSnO2 based composite electrical contact materials doped with various amounts of TiO2 reinforcement were produced by powder metallurgy and mechanical alloying techniques. First of all, starting powders were mixed to prepare powder mixtures having different chemical compositions. Powder mixtures were then milled in a high-energy planetary-type ball mill to achieve homogeneously mixed composite powders, followed by pressing in a closed die to obtain green compacts with a cylindrical shape, and sintering under vacuum to obtain composites. Composites were subjected to electrical wear tests under inductive loads to investigate the arc-erosion performance of electrical contacts in a new life-test rig designed and built for this work. Surface deteriorations and mass losses of electrical contacts were also evaluated as a function of increasing TiO2 reinforcement. Characterization of the starting and composite powders, green compacts, composites and arc-originated surface deteriorations was carried out using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The degree of particle size reduction was found to be higher in compositions having 3 to 7 wt% TiO2 than that in 1 % TiO2. Hardness of the composites was increased with increasing TiO2 content. In addition, porosity ratio was found to decrease up to 1 % TiO2 and to increase from 3 to 7 % TiO2. Comparison between surface morphologies and mass losses of arc-eroded specimens reveals that the Ag8SnO2-5TiO2 composite exhibits optimum arc-erosion performance among all compositions. The Ag8SnO2-5TiO2 composite was also subjected to several sintering tests thereafter to improve its physical, mechanical and wear properties. Optimum sintering time was determined as 5 h.
Key Words: Arc-erosion test rig, Electrical contact materials, Mechanical alloying, Metal matrix composites, Powder metallurgy, TiO2
|
