Refined martensite and enhanced strength of selective laser melted Ti6.5Al2.5Zr1Mo1V matrix composites by minor nano TiBw addition

To achieve strength improvement while ensuring a certain degree of plasticity of titanium matrix composites (TMCs) by selective laser melting (SLM), minor TiB 2 particles were used to fabricate in situ TiB whiskers (TiBw) reinforced Ti6.5Al2.5Zr1Mo1V composites in this work. It is found that pore defects in the as-printed TMCs reduce with the decreasing energy density. The porosity of as-printed TMCs decreases to 0.0005% under an optimized energy density of 61 ​J·mm −3 . To establish the relationship between porosity and SLM parameters, a systematic investigation of the influence of SLM parameters on the microstructure of TMCs is conducted, and the microstructure evolution is clarified during complex thermal cycling. The nano TiBw effectively hinders the coarsening of hierarchical martensite during the complex thermal cycles. As a result, the martensite plate thickness is approximately 60% in comparison with the as-printed Ti6.5Al2.5Zr1Mo1V alloy. A remarkable strengthening effect is achieved with minor TiBw, resulting in an impressive tensile strength of 1432 ​MPa and yield strength of 1320 ​MPa, while an elongation rate of 4.0% is maintained.