Development of beta-type Ti-Nb-Zr-Mo alloys for orthopedic applications

This study investigated the microstructure, mechanical properties, and cytocompatibility of the newly designed beta (β)-type Ti-Nb-Zr-Mo (TNZM) alloys for orthopedic applications. The fabrication method of TNZM alloys was cold-crucible levitation melting, their nominal compositions (wt.%) were Ti-24Nb-38Zr-2Mo (TNZM1), Ti-27Nb-33Zr-2Mo (TNZM2), Ti-30Nb-28Zr-2Mo (TNZM3) and Ti-37Nb-16Zr-2Mo (TNZM4). Microstructural investigation revealed four TNZM alloys consisted of body-centered-cubic structure (β-type) as their primary phase, with identical coarse grains and dense sub-grain boundaries. The Vickers hardness descended as TNZM2 (244 ± 8 HV) > TNZM1 (239 ± 6 HV) > TNZM3 (235 ± 6 HV) > TNZM4 (220 ± 6 HV); no significant difference was found among the compressive yield strengths of TNZM alloys, although TNZM4 showed a slightly lower flow stress than those of the other three alloys as the strain increases. Tensile properties of TNZM alloys were measured in the ranges of 592–702 MPa (tensile strength), 584–695 MPa (tensile yield strength), 10–16% (elongation to failure) and 68–73 GPa (Young's modulus). Cytocompatibility tests indicated that all TNZM alloys possessed good cytocompatibility. Thus, TNZM1, TNZM2 and TNZM3 were recommended as promising candidates for orthopedic applications as they possess higher elastic admissible strain (0.95–0.99%) than those of Grade-4 commercially pure titanium and mill-annealed Ti-6Al-4V alloy, high Vickers hardness, ultrahigh malleability, and good cytocompatibility.