Non-destructive observation of internal fatigue crack growth in Ti–6Al–4V by using synchrotron radiation μCT imaging

The propagation of an internal fatigue crack in Ti–6Al–4V was non-destructively observed by synchrotron radiation μCT imaging to clarify the crack growth rate in very high cycle fatigue. The results show that the internal crack propagated quite slowly at a rate of less than 10^?10 m/cycle. The propagation rate of an internal crack was compared with that of a surface crack in air and in high vacuum to examine the internal fracture process in terms of the environment around the crack. The rate of the internal crack was similar to that of the surface crack in high vacuum, but was significantly lower than that in air. This led us to conclude that the low propagation rate of the internal crack is due to the vacuum-like environment inside the crack.