Microstructures and mechanical properties of WCP/Ti-6Al-4V composite coatings by laser melt injection and laser-induction hybrid melt injection

Abstract

To improve the coating thickness and process efficiency of conventional laser melt injection (LMI), we introduced laser-induction hybrid melt injection (LIHMI) to prepare spherical WC particle (WCP)-reinforced metal matrix composite coatings on a Ti-6Al-4V substrate. The laser-induction hybrid melt injected coatings were 2.0–2.2 times thicker than that of the conventional laser melt injected coatings. The microstructure and mechanical properties of the WCP/Ti-6Al-4V composite coatings by LMI, LIHMI with induction preheating (pre-LIHMI) and LIHMI with induction preheating and post heating (pre/post-LIHMI) was investigated systemically. LIHMI inhibited the nucleation of primary TiC dendrites in the laser molten pool between adjacent WCP; therefore, the total amount of TiC in the laser-induction hybrid melt injected coatings was far less than that in the laser melt injected coatings. We found that (5.6–5.8)% TiC, β-Ti, and β-Ti/α-Ti formed in the laser-induction hybrid melt injected coatings, while 23% TiC, (Ti,W)C1-X and β-Ti formed in the laser melt injected coatings. In addition, pre/post-LIHMI led to a drastic WCP/Ti interfacial reaction due to the long dwell time and high temperature of the laser molten pool, which greatly deteriorated the mechanical properties of the coatings. Compared with those of the pre/post-LIHMI samples, the pre-LIHMI samples exhibited a shorter liquid residence time and lower temperature of the laser molten pool and a more moderate WCP/Ti interfacial reaction. In addition, tension strength of pre-LIHMI sample and pre/post-LIHMI sample is 34% and 12% higher than that of LMI sample.