Effects of vacuum environment on small fatigue crack propagation in Ti-6Al-4V

Small fatigue crack propagation tests were conducted on Ti-6Al-4V in ultrahigh vacuum, air, and argon to clarify the effects of vacuum on crack propagation processes. The crack propagation rate in vacuum was significantly lower than that in air. The crack propagation rate in argon agreed with that in air in the small crack regime; however, it became similar to that in vacuum in the long crack regime. This indicates that the existence of gases has significant effects in the small crack regime, even if they are chemically inert. These results led us to conclude that, in addition to chemical inactivity, the absence of physical adsorption plays an important role in the retarding effect of vacuum on small crack propagation.