Effect of Short-Time Heat-Treatment and Fine-Particle Bombarding on Fatigue Strength of Ti-6Al-4V Alloy

This study was conducted to investigate the effect of short-time heat-treatment and fine-particle bombarding (FPB) on the fatigue strength of Ti-6Al-4V alloy. The short-time heat-treatment was performed at 953~1203 K for 60 s. Then, the changes in hardness and mechanical properties were investigated. The yield strength was greatly decreased by the above heat-treatment conducted at 1103 K and the reduction in area was strikingly increased. On the other hand, the yield strength was increased by the heat-treatment conducted at 1203 K and the reduction in area was at a higher level than that of the untreated material. When the untreated material and the above heat-treated materials were further FPBed, the surface hardness was greatly increased and compressive residual stress was introduced. It was clearly observed on the fracture surfaces that the fatigue cracks of the FPBed materials were initiated from the substrates due to the existence of the hardened layers. This result showed that the fatigue strength of the FPBed materials were strongly controlled by the strength of the substrate. Actually, the highest fatigue strength was achieved by the heat-treatment at 1203 K and FPB because this heat-treatment remarkably improved the strength of the substrate.