放射光マイクロCTによるTi-6Al-4Vの内部疲労き裂の発生・進展過程の非破壊観察

抄録

The initiation and growth of internal fatigue crack in Ti-6Al-4V were non-destructively observed using synchrotron radiation micro-CT at the large synchrotron radiation facility SPring-8. From the observation result, the initiation life and growth rate of internal cracks were measured. Numbers of cracks were detected by repeating a combination of a fatigue test and micro-CT. The initiation lives of these cracks were widely different from each other. The crack length just after the initiation was measured, and the relationship between the crack initiation life and the size of crack origin was investigated. As a result, the initiation lives had no apparent relationship with the initial crack lengths; that is, there is a possibility that the size of crack origin, which is a facet formed at α phase, had no influence on the following growth behavior. Additionally, the crack growth behaviors had nothing to do with their initiation lives; for example, some cracks with short initiation lives didn't show apparent growth for a while after initiations. The growth rate of internal crack was less than 10^-10 m/cycle, and was significantly lower than that of surface crack. The slow growth rate of internal crack might be due to the vacuum-like environment inside the crack.