Titanium boride and titanium silicide phase formation by high power diode laser alloying of B4C and SiC particles with Ti: Microstructure, hardness and wear studies

In this work a novel multiphase titanium metal matrix composite (TMMC) coating was developed by high power diode laser assisted alloying of Cp-Ti with the preplaced Boropak powder consisting of B4C and SiC ceramic particles. The XRD, optical microscopy, scanning electron microscopy, EDAX, microhardness and wear testing techniques were employed to investigate structural phase, hardness and wear properties of the alloyed coating. Under the influence of multipass laser alloying, the B4C and SiC ceramic particles decompose to yield boron, silicon and carbon species that react with molten titanium to form TiB2, TiB, TiC and Ti5Si3 phases in the laser alloyed coating. In addition, the un-melted B4C and SiC ceramic particles are dispersed in the titanium matrix. Microstructure of the alloyed coating consists of dendrites and coralline-like structure. The tips of the coralline-like structure are in the range of 150-500 nm. The ceramic multiphase TiB2, TiB, TiC and Ti5Si3 formation resulted in average microhardness around 800-2200 HV0.2 at different regions of the TMMC coating cross section. To correlate the phase formation and microstructural features, surface temperature evolved at the interaction area during laser surface alloying was estimated by a simple equation. Activation energy for the laser melted track was calculated using the Arhennius equation. The linear reciprocating wear test performed on laser alloyed coating against WC ball showed wear rate value of 1.623 x 10(-4) mm(3)/N.m which is 6 times lower compared to the untreated titanium.