日本金属学会誌

J. Japan Inst. Met. Mater, Vol. 80, No. 12 (2016),
pp. 764-771

Change in Mechanical Properties of Biomechanical Ti-12Cr Subjected to Heat Treatment and Surface Modification Processing

Kentaro Niwa1, Toshikazu Akahori2, Mitsuo Niinomi2, Tomokazu Hattori2 and Masaaki Nakai3

1Graduate School of Science and Technology, Meijo University, Nagoya 468-8502
2Faculty of Science and Technology, Meijo University, Nagoya 468-8502
3Faculty of Science and Technology, Kinki University, Higashiosaka 577-8502

Abstract:

In recent years, metallic biomaterial applications have demanded a relatively low elastic modulus of around 30 GPa that is nearly equal to that of bone. 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. Therefore, Young's modulus control by stress-induced transformation in a newly developed biomedical β-type Ti-12Cr alloy, has been proposed by the present authors. However, the relationship between the microstructure and mechanical properties of Ti-12Cr has not been fully investigated up till now.
Therefore, changes in the mechanical properties of Ti-12Cr were investigated through heat treatment and the fine particle bombarding process (FPB), which is a surface modification process used in this study. Peak aging of Ti-12Cr heated at 673 K showed for around 2.4 ks.
The Vickers hardness of Ti-12Cr in the peak aging condition (PA) at 673 K was around 90% (HV 524) higher than that (HV 294) in the solutionized condition (ST). Meanwhile, both the 0.2% proof stress and tensile strength of Ti-12Cr in the PA at 673 K were also around 50% higher those in the ST. However, the ductility of Ti-12Cr in the PA at each temperature reduced significantly. Therefore, a solo-solution treatment was judged to be the optimal heat treatment for Ti-12Cr with an excellent combination of strength and ductility. The Vickers hardness and Young's modulus of as-solutionized Ti-12Cr subjected to FPB increased by around 40% and 70%, respectively, at the very edge of the specimen surface, as compared to those of the unprocessed sample. Furthermore, the fatigue strength of Ti-12Cr subjected to FPB increased by around 70 MPa. The bone contact ratio of Ti-12Cr rose slightly with an increase in the implantation period from 24 to 52 weeks.

[doi:10.2320/jinstmet.J2016036]


(Received 2016/6/6)

Keywords:

metallic biomaterial, stress-induced phase, mechanical strength, surface modification, biocompatibility


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