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

Abstract

The present study concerns development of a hard in situ titanium boride-dispersed Al matrix composite layer on Al substrate with an objective to improve wear resistance property. Laser composite surfacing was carried out by melting the surface of sand blasted commercially pure Al substrate using a continuous wave CO₂ laser and simultaneous deposition of a mixture of K₂TiF₆ and KBF₆ (in the weight ratio of 2 : 1) through an external feeder (at a feed rate of 4 g/min) using Ar as shrouding environment. The process variables used in the present study were applied laser power and scan speed. Following laser irradiation, a detailed characterization of the composite layer was undertaken in terms of microstructure, composition and phases. Important mechanical properties like microhardness and wear resistance were evaluated in details. Irradiation results into melting of the substrate along with the delivered powder mixture, intermixing and rapid solidification to form the composite layer on the surface of the substrate. The microstructure of the composite layer consisted of uniformly dispersed TiB₂ and TiB particles in Al matrix. The microhardness of the surface was improved (to a maximum of 3 times) as compared to that of as-received Al substrate. There was a significant improvement in wear resistance in composite surfaced Al as compared to as-received one. However, corrosion property in a 3.56 wt.% NaCl solution was marginally deteriorated because of the presence of boride phase in the matrix.