三次元積層造形によるTi-6Al-4V合金の疲労強度に及ぼす空孔の影響

抄録

In this study, the effects of porosities in additive manufactured Ti-6Al-4V alloy on fatigue strength were invedtigated. Fatigue tests and observations of fracture surface on HIP'd (Hot isostatic pressed) and Non-HIP'd specimens were conducted. Fatigue lives of Non-HIP'd specimens were shorter than those of HIP'd. It was observed that fatigue fracture of all Non-HIP'd specimens occurred from porosities near the specimen surface. On the other hand, porosities didn't exist in fracture surface of HIP'd specimens. It was considered that existence of porosities caused shortened fatigue lives of Non-HIP'd specimens. Stress intensity factor ranges at fracture origins were examined by simulation. As a result, all of them were larger than threshold stress intensity factor range. It was considered that porosities of Non-HIP'd specimens act as initial cracks and fatigue crack grows from the initial crack. To confirm above assumption, fatigue lives of Non-HIP'd specimens were estimated by of fatigue crack growth law. It was found experimental data were plotted in the range of estimated fatigue lives based on fatigue crack growth analysis. There is a possibility that crack growth life is dominant for fatigue life of Non-HIP'd specimen with porosities.