Effects of Zr Addition on the Microstructural Evolution, Mechanical Properties, and Corrosion Behavior of Novel Biomedical Ti-Zr-Mo-Mn Alloys

beta-Type Ti alloys have been widely investigated as implant materials owing to their excellent mechanical properties, corrosion resistance, and biocompatibility. In the present work, the effects of Zr on the microstructure, mechanical properties, and corrosion behaviors of Ti-Zr-Mo-Mn alloys were systematically studied. With the increase of Zr content, the phase composition gradually changed from intragranular-alpha + beta of (TZ)(5:1)MM alloy to grain-boundary-alpha + beta of (TZ)(2:1)MM alloy and finally transferred to a single beta phase structure of (TZ)(1:1)MM alloy. The (TZ)(1:1)MM alloy exhibited a good mechanical combination with a yield strength of 750.8 MPa, an elastic modulus of 61.3 GPa, and a tensile ductility of 14.6%. Moreover, the addition of Zr can effectively stabilize the passivation film and reduce the sensitivity of microgalvanic corrosion in simulated body fluid, leading to enhanced corrosion resistance in the TZMM alloys. X-ray photoelectron spectroscopy analysis together with the ion-sputtering technique revealed that the passivation films formed on TZMM alloys possessed a bilayered structure (outer Ti+Zr mixed-oxide layer and inner Zr-oxide-rich layer), in which the inner Zr oxide layer plays an important role in the corrosion resistance of the TZMM alloys. In vitro biocompatibility evaluations demonstrated that the TZMM alloys can support cell adhesion and proliferation with high biocompatibility comparable to that of CP-Ti, while in vivo biocompatibility evaluations validated the bone osteointegration ability of TZMM alloys after long-term implantation. The above results indicate that novel TZMM alloys are promising candidates for implant material.