2014 年 80 巻 818 号 p. SMM0296
Aiming at an enhanced fatigue strength of Ti-6Al-4V alloys, the severe plastic deformation was given to the specimen surface at the final stage of lathe turning. The main findings of this study can be summarized as follows. A chip with unique shape for the surface treatment was developed. By using the chip, a fine-grained structure was formed on the entire surface of the Ti-6Al-4V alloy specimen during the cutting and rubbing process. The fine-grain structure with 500nm grain size was generated at about 20μm below the surface. Vickers hardness values (HV) of the specimen surface after the cutting and friction processing was reached about HV of 500 (40% higher than preprocessing). Although some studies indicated negligible increases in fatigue strength of titanium alloy specimen processed by surface treatments such as nitriding, shot-peening, the fatigue life of the cutting and friction processed specimen was much longer than that of non-surface treated specimens. Regarding the fatigue strength at 107 cycles, no enhancement due to the present surface processing was attained, because of the fish-eye fracture. The fracture was brought by the cracking of α grains located beneath the fine-grain surface layer.