Estimation of the fatigue crack initiation site and life of Ti-6Al-4V alloy for two types of circle and slender crystal grains

Abstract

In this study, the fatigue crack initiation behaviour and fatigue crack initiation life of the Ti-6Al-4 V alloy, which had circular and slender grains, were quantitatively evaluated based on slip line length and out-of-plane component of Schmidt factor. As the results, in crystal grains where fatigue cracks initiated, the slip system that contributes to crack initiation could be identified by considering the out-of-plane component of the Schmidt factor (SFsinΩ), and the fatigue cracks were initiated by the basal slip of the primally α phase in all specimens. Furthermore, regarding the prediction of the location of fatigue crack initiation, it is clear that the grains that are candidates for fatigue crack initiation could be estimated based on the relationship between the slip line length of the basal slip system that contributes to crack initiation in each grain and SFsinΩ. Finally, the macro fatigue crack initiation life could be estimated using a parameter of P that combines micro crack initiation driving force Pi and micro crack propagation driving force Pp.