Effect of heat treatment on microstructure, mechanical and tribological properties of in-situ (TiC+TiB)/TC4 composites by casting

To enhance the performance of in-situ synthesized 6vol.% (TiC+TiB)/TC4 titanium matrix composites fabricated by casting, a variety of heat treatment processes were carried out. Upon conducting microstructure observations following various heat treatments, it was found that the composites exhibit a basketweave microstructure, consisting of an α phase and a transformed β phase. The sizes of (α+β) phases were found to be refined to varying degrees after the heat treatment processes, while the morphology of TiB remains largely unchanged and TiC becomes granulated. Compressive testing revealed that all composites subjected to different heat treatments demonstrate a notable increase in ultimate compressive strength as well as a slight improvement in plasticity compared to the as-cast state. The results of the tribological performance test indicated that the heat-treated composites exhibit lower average friction coefficient, specific wear rate, and worn surface roughness compared to the as-cast composite. Among the heat treatment processes studied, the composite solution heated at 1,150 °C/1 h followed by air cooling, then 950 °C/1 h followed by air cooling, and finally 500 °C/4 h followed by air cooling, demonstrates the highest levels of hardness, compressive strength, and wear resistance. These improvements are attributed to the combined effects of solid solution strengthening, grain refinement, and the pinning of dislocation slip.