Mechanical behavior and phase transformation of β-type Ti-35Nb-2Ta-3Zr alloy fabricated by 3D-Printing

Additive manufacturing (AM) has a substantial capability to produce superior and divergent properties of titanium alloys for biomedical implants, unlike the existing conventional technologies. This work investigated the mechanical properties and microstructure evolution of a beta-type Ti-35Nb-2Ta-3Zr alloy prepared by selective laser sintering (SLS) process. The superelastic properties of the resultant specimen were characterized by cyclic loading-unloading tensile testing to evaluate the effect of SLS-process on the beta-type Ti alloy specimen. The zigzag and V-shaped formation of {112}<111>(beta) twins, coexisting with stress-induced omega-formation, were observed by the transmission electron microscopy (TEM). The formation of Type I twin martensite along with beta-structure is attributed to superelastic recovery and elastic recovery of SLS-produced specimen. High resolution TEM (HRTEM) observation was used to investigate the transition between beta and omega phases. Thin layers of omega-formation in weak interfacial stress regions along with the longitudinal twin boundaries were also analyzed. The orientation relationship between omega-structure and parent beta-phase involves an overlapping of omega-phase, observed along with longitudinal beta-matrix and beta-twins. Moreover, dislocation tangles and dislocation pile-ups form along with twin martensite, stress-induced omega-phase, and beta-phase. (C) 2019 Elsevier B.V. All rights reserved.