Effect of B4C Content on the Microstructure and Hardness of In-Situ Formed (TiB + TiC)/TC4 Composites

To enhance the hardness and wear resistance of TC4 titanium alloy, (TiB + TiC)/TC4 matrix composites were fabricated by powder metallurgy using B4C as an in-situ reaction reinforcement and SiO2 as a sintering aid. The influence of B4C mass fractions (0, 5, 10, 15, 20 wt%) on microstructure and microhardness was systematically investigated. Results indicate that densification initially increases and then decreases with B4C addition, peaking at 5 wt%. At this composition, in-situ generated TiB and TiC phases are finely dispersed and tightly bonded to the matrix. The SiO2 sintering aid enhances atomic diffusion through interfacial reactions, facilitating in-situ formation and densification. Microhardness exhibits the similar rising-then-falling trend, reaching 61.9 HRC at 5 wt% B4C (a 23.1% increase over the B4C-free matrix of 50.3 HRC). However, excessive B4C causes structural loosening and a consequent hardness reduction. This study offers experimental guidance for tailoring the composition and improving the performance of B4C-reinforced TC4 composites.