Non-destructive measurement of internal small fatigue crack growth rate in Ti-6Al-4V

Abstract

Observations of internal small fatigue crack growth in Ti-6Al-4V were conducted using synchrotron radiation μCT imaging at SPring-8 to obtain the internal crack growth rate. The just-initiated internal cracks and their growth processes were successively observed. The internal small cracks propagated very slowly with the growth rate of less than 10-10 m/cycle. The crack growth rate had a lot variability in the smaller crack length regime. In order to discuss the reason for the small growth rate of internal crack in terms of the effect of environment inside the crack, the internal crack growth rate was compared with the surface crack growth rate in air and ultra-high vacuum. As a result, the internal crack growth rate was lower than the surface crack growth rate in air, and matched with that in ultra-high vacuum in the longer crack length regime. However, the growth rate of internal crack was smaller than that of surface crack in ultra-high vacuum in the relatively smaller crack length regime. These results indicate the possibility that the differences in vacuum pressure have a dominant effect on the small crack growth length, and that the gas contained in the alloy plays an important role in the internal small crack growth.