2017 Volume 58 Issue 6 Pages 951-957
In recent years, metallic biomaterial applications have demanded a relatively low Young's modulus that is nearly equal to that of bone (around 30 GPa). However, in the case of spinal fixture applications, metallic materials with a relatively high Young's modulus are required to suppress spring-back by elastic and plastic deformation during implantation. We recently proposed Young's modulus control by stress-induced transformation to produce the biomedical β-type Ti–12Cr alloy. However, the relationship between the microstructure and the mechanical properties of Ti–12Cr has not been fully investigated. In this study, the changes in the mechanical properties of Ti–12Cr were investigated through the heat treatment and the fine particle bombarding process (FPB), which is a surface modification process. Peak aging (PA) of Ti–12Cr heated at 673 K occurred for around 2.4 ks. The Vickers hardness of Ti–12Cr at the PA condition at 673 K (HV 524) was around 90% higher than that after solutionized treatment (ST) (HV 294). Both the 0.2% proof stress and tensile strength of Ti–12Cr at the PA condition at 673 K were also around 50% higher those after ST. However, the ductility of Ti–12Cr at the PA condition at each temperature significantly decreased. Therefore, only ST was judged to be optimal for Ti–12Cr with an excellent combination of strength and ductility. The Vickers hardness and Young's modulus of solutionized Ti–12Cr subjected to FPB increased by around 40% and 70%, respectively, at the edge of the specimen surface compared with the corresponding values of the unprocessed sample. Furthermore, the run-out (770 MPa) of Ti–12Cr subjected to FPB increased by around 70 MPa. The bone contact ratio of Ti–12Cr slightly increased with an increase in the implantation period from 24 to 52 weeks.
This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 80 (2016) 764–771.