Micromechanics of crack propagation in Ti-6Al and Ti-6Al-4V

Studies have been conducted of sustained load cracking and accelerated fatigue crack growth under dwell conditions in Ti alloys. It has been shown that accelerated fatigue crack growth is dependent on alloy composition and microstructure, as well as temperature and internal hydrogen content. The relationship between crack velocity and microstructure, alloy content, temperature and hydrogen concentration has been rationalized on the basis of a micromechanical model. Increases in crack growth rate up to a factor of thirty were observed for hold-time testing, the magnitude of the increase being dependent on microstructure, hydrogen content and test temperature. Such increases were often associated with a fracture mode transition from striations to a cleavage-like fracture of primary alpha particles in the equiaxed alpha microstructures. 8 references