In-situ dispersion of titanium boride on copper by laser composite surfacing for improved wear resistance

Abstract

The present study concerns the development of a hard in-situ titanium boride dispersed in a composite layer on a copper substrate with the objective of improving the wear resistance. Laser composite surfacing was carried out by melting the surface of a sand blasted commercially pure copper substrate using a continuous wave CO₂ laser (with a beam diameter of 3.5 mm) and the simultaneous deposition of a mixture of K₂TiF₆ and KBF6 (in the weight ratio of 2:1) using an external feeder (at a feed rate of 4 g/min) and Ar as shroud. The process variables used in the present study were the laser power applied and the scan speed. Following the laser irradiation, a detailed characterisation of the composite layer was undertaken in terms of microstructure, composition and phases. Surface dependent mechanical properties such as micro-hardness and wear resistance were also evaluated in detail. Irradiation resulted in melting of the substrate, along with the delivered powder mixture, intermixing and rapid solidification. The microstructure of the composite layer consisted of uniformly dispersed titanium boride particles in a grain-refined copper matrix. The micro-hardness of the surface was improved threefold as compared to that of as-received copper substrate. There was a significant improvement in the wear resistance of the composite surfaced copper, as compared to that of the as-received copper. The mechanism of wear was investigated.