Silver Alloy Surface Modification for Mechanical Property Enhancement in Aviation and Transportation

Abstract

Silver alloys are often used for electrical switches in railway transportation. However, a well-known issue with these switches is their relatively short application period due to certain disadvantages of silver alloys, mainly their low hardness and low resistance to abrasive wear, in contrast to their excellent electrical conductivity. Therefore, the main goal of this study was to increase or maintain the hardness of the surface layer in order to extend the life of worn parts without compromising their electrical properties. Instead of ceramic particles, as in other studies, metallic powders were used, which could increase the electrical and/or thermal properties of silver alloys. The following work presents the use of laser processing as a relatively new technique for metal and metal alloy surface processing technology. In particular, a process based on the melting of silver (Ag) with metallic powders, such as chromium (Cr) and nickel (Ni) particles, is presented. The aim was for these powders to create intermetallic phases with a silver matrix in the obtained surface layer, significantly improving the mechanical properties based on the formation of the phases coherent or semi-coherent with the silver matrix. Regarding the original practical implications of this work, it was important to investigate the possibility of applying fibre laser for surface property enhancement. The scientific aim was to describe the changes in microstructure and compounds that occurred in the laser-remelted surface silver layer after Ni and Cr particles were fed into the basic silver material. It was concluded that the surface layer obtained after chromium application was without cracks and defects and had a higher hardness than the untreated material. A three-zone structure was also found in the obtained surface layer: (1) the remelted zone, (2) the heat-affected zone, and (3) the matrix material. The remelting zone revealed a higher hardness compared to the untreated material, reaching 92 HV0.3, which is more than twice the initial hardness value.

Keywords

• surface treatment
• fibre laser
• silver alloys
• laser feeding
• metal powder