Fatigue crack growth behaviour of a near alpha titanium alloy Timetal 834 at 450 degree C and 600 degree C

Fatigue crack growth behaviour of a near alpha titanium alloy Timetal 834 has been studied at maximum dynamic strain ageing temperature (450 degree C) and at the service temperature (600 degree C). Compact-tension type fracture mechanics specimens have been tested with stress ratio and frequency of 0.1 and 1 Hz, respectively, under constant amplitude loading. The alloy showed higher crack growth rate at 450 degree C due to dynamic strain ageing which causes higher stress concentration at the crack tip as compared to 600 degree C. The pronounced effect of oxide and roughness induced crack closure revealed from Auger electron spectroscopy and surface profiler, respectively, have been attributed to reduce the stage I as well as stage II fatigue crack growth rate at 600 degree C. Fractographic and crack path observations confirmed that the crack growth mechanism remained highly faceted in nature at low IK levels which changes subsequently to striation mode of fracture at relatively higher IK levels.