Refined microstructure and enhanced wear resistance of titanium matrix composites produced by selective laser melting
Optics and Laser Technology
School of Engineering
Outstanding Youth Foundation of Jiangxi Province Natural Science Foundation of Tianjin Department of Education of Guangdong Province Project of Engineering Research Centre of Foshan
© 2020 Elsevier Ltd In order to investigate the effect of TiB2 contents on the microstructure and wear resistance of titanium matrix composites, commercial pure Ti (CP-Ti) powders with 0–7.5 wt.% TiB2 particles were melted by selective laser melting (SLM) to produce the in-situ Ti-TiB composites. When the TiB2 content increases from 2.5 wt.% to 7.5 wt.%, the microstructures of the Ti-TiB composites undergo a transition from the single phase of α′-Ti to the mixed phases of α′-Ti, TiB and TiB2, and the acicular α′-Ti is refined significantly from 1.03 ± 0.24 μm to 0.36 ± 0.05 μm, showing that increasing the TiB2 content induces the formation of TiB and refines the microstructure. Moreover, large TiB2 particles are not melted completely and they react with the Ti matrix liquid to form a TiB layer around the Ti matrix during SLM. However, small TiB2 particles are completely dissolved into the Ti matrix liquid so that the eutectic TiB grains are precipitated at the boundaries of the Ti matrix after in-situ reaction of TiB2 with Ti. The formation of α′ martensite in the titanium matrix and the addition of TiB2 can induce the fine grain strengthening, the dispersion strengthening, the solid solution strengthening in the SLM-produced composites. The results indicate that the microhardness of the composites increases from 258 ± 10.3 HV0.2 to 435 ± 14.7 HV0.2. The wear process of the SLM-produced CP-Ti and TiB2 reinforced Ti matrix composites is accompanied by adhesion wear, abrasive wear and oxidation wear. As a result, when the TiB2 content increases to 7.5%, the wear resistance of the composites increases by 32.6% compared with that of the CP-Ti. These improvements are mainly due to strengthening and hardening effects induced by TiB2 particles and refinement of Ti matrix. This study provides some basis for developing wear-resistant and high-strength titanium alloys.