ショットピーニングを施した医療用コバルトクロム合金の疲労特性

抄録

Co-Cr alloy is widely used as implant materials. The design life of artificial joints is 10 to 20 years and the increase in durability is required as the aging of society is expected. Most of the artificial joints are currently made by European and American manufacturers and their applications to small physiques, including Japanese women, are not fully expected. There are difficulties in current materials to create thinner and longer implants to suit and fulfill the requirements depending on the bone shape. Therefore, it is necessary to improve the fatigue properties of Co-Cr alloys. Shot peening (SP) is one of the methods to improve these parameters. In this study, bending fatigue tests and observation of surface morphology, crystalline structure analysis were conducted on SP-treated medical grade Co-Cr alloys. Surface roughness and hardness distribution showed typical values compared to present research. EBSD analysis showed strain-induced martensitic transformation (SIMT) and refinement of crystal grains near the SP-treated surface. These effects were remarkable among specimens treated by high hardness projection materials and high coverage. Fatigue test revealed that the fatigue limit of the SP-treated specimen was improved by 77%. However, there were no significant differences in fatigue strength between SP-treated specimens under various conditions. Saturation of martensite transformation near the surface and equivalent compressive residual stress may be the primary effect to fatigue properties compared to surface roughness and hardness.