Microstructural Evolution, Mechanical Properties and Tribological Behavior of B₄C-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 B₄C-reinforced Ti composites. The effect of volumetric energy density (VED) on the relative density, microstructural evolution, tensile properties and wear behaviors of B₄C-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/mm³). The additive particulates B₄C 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 VED increases. Through the analysis of the tensile and wear tests, the sample at 61 J/mm³ VED 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^-4 mm³·N^-1m^-1. The microstructural evolution in VED changes and the corresponding underlying strengthening mechanisms of LPBF-ed Ti + B₄C composites are conducted in detail.