Microstructural Evolution, Mechanical Properties and Tribological Behavior of BC-Reinforced Ti In Situ Composites Produced by Laser Powder Bed Fusion.

Based on the advantage of rapid net-shape fabrication, laser powder bed fusion (LPBF) is utilized to process BC-reinforced Ti composites. The effect of volumetric energy density () on the relative density, microstructural evolution, tensile properties and wear behaviors of BC-reinforced Ti composites were systematically investigated. The LPBF-ed samples with high relative density (>99%) can be achieved, while the pores and un-melted powders can be observed in the sample owing to the low energy input (33 J/mm). The additive particulates BC were transformed into needle-like TiB whiskers with nano-scale while C dissolved in the Ti matrix. Fine-scale grains (<10 μm) with random crystallographic orientation can be achieved and the residual stress shows a downtrend as the increases. Through the analysis of the tensile and wear tests, the sample at 61 J/mm showed a good combination of strength and wear performance, with an ultimate tensile strength of 951 MPa and a wear rate of 3.91 × 10 mm·Nm. The microstructural evolution in changes and the corresponding underlying strengthening mechanisms of LPBF-ed Ti + BC composites are conducted in detail.