Compression fatigue behavior of Ti-6Al-4V mesh arrays fabricated by electron beam melting

This paper focuses on the compression fatigue behavior of Ti-6Al-4V mesh arrays with high porosities of ∼60-85%, which were fabricated by an additive manufacturing technique using electron beam melting. The results show that their fatigue lives are mainly determined by uniform deformation through the entire specimens, while their failures are characterized by rapid strain accumulation and a severe crush band at an angle of 45° to the cyclic loading direction. The relation between the relative fatigue strength and relative density can be evaluated by the well-known Gibson-Ashby model with the exponential factor n being 2.7, which is higher than the reported data for aluminum and nickel foams, and almost double the idealized value (n = 1.5) of a stochastic open cellular foam. The underlying mechanism of fatigue failure appears to be interaction between cyclic ratcheting and fatigue crack initiation and propagation, while the former plays a dominant role in fatigue life. TEM observations found that dislocations are generated along the interface of the α′ phase and their generation becomes more evident with an increase in the relative density. This would contribute to the retardation of cyclic ratcheting and an improvement in the fatigue strength.