Change in mechanical strength and bone contactability of biomedical titanium alloy with low young's modulus subjected to fine particle bombarding process+1

Beta-type Ti-29Nb-13Ta-4.6Zr (TNTZ), which is a recently developed biomedical titanium alloys, shows a relatively low Young's modulus of around 60 GPa when subjected to a solution treatment. However, our focus in this study was on the practical applications of TNTZ in vivo because its mechanical strength decreases with solution treatment progress. Therefore, we investigated the effect of fine particle bombarding (FPB) on the mechanical properties of TNTZ subjected to a cold-swaging treatment in order to maintain its relatively low Young's modulus and to improve its mechanical properties. The relative bone contact ratios between the cancellous bones of Japanese white rabbits and column-shaped TNTZ samples subjected to FPB were also evaluated. The microstructure of cold-swaged TNTZ showed a single beta-phase with a marble-like structure. Moreover, its Vickers hardness did not increase remarkably with changes in its diameter, although the average diameter of the beta-grains of solutionized TNTZ ranged from 5.0 to 20 μm, depending on the increase in the holding time of the solution treatment. The Vickers hardness and Young's modulus of TNTZ subjected to FPB increased at the edge of the specimen surface to be around 70% and 15%, respectively, more than those of cold-swaged TNTZ. Further, the fatigue strength of TNTZ subjected to FPB became significantly higher than that of cold-swaged TNTZ in the high-cycle fatigue life region. Lastly, TNTZ with a rough surface texture (Ra: 0.65 μm) showed a relative bone contact ratio of more than 80% after undergoing FPB; this value was significantly higher than that of cold-swaged TNTZ with a very smooth surface texture (Ra: 0.07 μm).