FATIGUE-CRACK PROPAGATION IN BETA-TI-15MO-5ZR-3AL ALLOY

Fatigue crack propagation(FCP)in beta Ti-15Mo-5Zr-3Al alloy has been studied in laboratory air for five different microstructures which were solution-treated at 700 degrees C, 735 degrees C, 765 degrees C, 850 degrees C, and 1000 degrees C followed by aged at 500 degrees C. With one exception, microstructure was found to have very little or no influence on FCP behaviour. The one exception was the microstructure having the largest beta grain size whose FCP resistance was higher than that of the other microstructures due to higher crack closure levels. The effect of stress ratio on FCP could not be realized only in terms of crack closure mechanism, because static fracture mechanisms operated in FCP behaviour depending on the magnitude of the maximum stress intensity factor. Furthermore, the FCP resistance of all the microstructures was considerably lower than that of alpha-beta Ti-6Al-4V alloy, which was primarily attributed to lower crack closure levels of the present alloy.