Microstructural evolution and wear properties of in-situ (TiB + TiC)-reinforced Ti6Al4V matrix composite coating by laser melting deposition

Abstract

In this study, a laser melting deposition (LDM) process was employed to deposit titanium matrix composite (TMC) coatings on a titanium alloy substrate by adding 1–5 wt% nanosized B4C particles, which were annealed at 900 °C. The microstructure and dry sliding friction behavior of TMC coatings were studied before and after the annealing treatment. The experimental results show that the TiB + TiC hybrid reinforced phase formed by the in-situ reaction of B4C and Ti matrix mainly precipitated at the grain boundary, providing the grain boundary and second-phase strengthening. Specific orientation relationships of TiB and TiC phases with the matrix phase were revealed, which had an essential effect on the microhardness distribution along the coatings. The annealing treatment promoted the diffusion of hybrid reinforcement into the matrix, strengthening their interface bonding, and has an significant impact on the wear properties of TMC coating. The room temperature friction coefficient (COF) of all the coatings remained relatively constant at 0.3–0.6. With increasing B4C content, the wear loss of the as-deposited coatings continually increased from 0.024 mm3 to 0.054 mm3, while the wear loss of the annealed TMC coatings are much lower than before, from 0.032 mm3 (TMC1) to 0.020 mm3 (TMC2) and then rise to 0.023 mm3 (TMC3). Scanning electron microscopy (SEM) morphologies determined that annealing reduced the abrasive and adhesive wear of TMC composite coating and improved its wear resistance.