In situ fabrication of a titanium-niobium alloy with tailored microstructures, enhanced mechanical properties and biocompatibility by using selective laser melting

A titanium-niobium (Ti-Nb) alloy with tailored microstructures, enhanced mechanical properties and biocompatibility was in situ fabricated by selective laser melting (SLM) using a blended powder with 25 wt.% Nb content. The effect of laser energy density from 70 J/mm3 to 110 J/mm3 on the phase transformation, microstructure, and mechanical properties of the SLM-printed Ti-25Nb alloy was investigated. The results indicate that the energy density of 110 J/mm3 results in the highest relative density and homogeneous element distributions in the alloy. The α' and β phases with an orientation relationship of [023]β//[-12-16]α' were identified through X-ray diffraction and transmission electron microscopy, and their proportions are crucially determined by the laser energy density. With an increase in the energy density, the microstructure of the Ti-25Nb alloy varies from acicular-shaped grains to coarsened lath-shaped grains and to lath-shaped grain + cellular-shaped subgrains, due to the decrease in cooling rate and the rise in temperature gradient. The yield strength and microhardness of the printed Ti-25Nb alloy decrease with the increase in energy density from 70 J/mm3 to 100 J/mm3, and then increase to the highest values of 645 MPa and 264 HV at 110 J/mm3, respectively. This variation of mechanical properties is dependent on both the coarsening of α' phase and the formation of β (Ti, Nb) solid solution. Besides, the SLM-printed Ti-25Nb alloy exhibits both the excellent in vitro apatite-forming capability and better cell spread and proliferation compared to pure Ti. Accepted version This work was supported by the National Natural Science Foundation of China (51775207), the National key R&D program of China, additive manufacturing and laser manufacturing key special subject of Chain (personalized implant prosthesis additive manufacturing process research, 2016YFB1101303), the Academic frontier youth team at Huazhong University of Science and Technology, the Science and Technology Major Project of Guangdong Province (2017B090911007) and Application Fundamentals frontier Major Project of Wuhan (2018010401011281). The authors are also grateful for the State Key Laboratory of Materials Processing and Die & Mould Technology and the Analysis and Testing Center of Huazhong University of Science and Technology for all the measurements.