Microstructural evolution, mechanical and tribological properties of TiC/Ti6Al4V composites with unique microstructure prepared by SLM

Based on the advantage of rapidly fabricating parts with complex geometric shapes, selective laser melting (SLM), an additive manufacturing technology, is utilized to process 3 wt.% TiC/Ti6Al4V composites. A TiC-reinforced Ti6Al4V composite with directionally grown unique microstructures is prepared by SLM. The effect of the laser power and scanning speed on the relative density, constitutional phases, and microstructure features is investigated systematically. The microstructure evolution mechanism is clarified. Moreover, the influence of the unique microstructure on the mechanical and tribological properties is investigated. The results indicate that the relative density of the SLM-processed TiC/Ti6Al4V composite can reach 98.7%. Because of the special processing technology used in SLM, unique nanoscale lamellar and needle-like eutectic TiC reinforcement phases, which have never been observed in TiC/Ti6Al4V composites prepared by other flexible laser additive manufacturing technologies, are formed. Furthermore, the composites are dominated by extremely small grains. The nanoscale eutectic TiC and refined grains significantly enhance the hardness and tensile strength of the composites. The microhardness and ultimate tensile strength reach 487 HV and 1565 MPa, respectively. More importantly, the nanoscale reinforcement promotes the migration of C and the formation of a dense solid lubricant film during friction, leading to excellent tribological properties at different applied loads. As the applied load increases from 5 N to 15 N, due to the enhancement of the effect of the nanoscale reinforcement, the tribological properties of the SLM-processed TiC/Ti6Al4V composites are further improved. At an applied load of 15 N, the friction coefficient and wear rate reach 0.303 and 1.221 mm3/m∙N, respectively.