Fatigue crack nucleation and growth behaviors of laser melting deposited Ti–6Al–2Zr–Mo–V

The fatigue crack nucleation and growth behaviors of laser melting deposited (LMD) Ti–6Al–2Zr–Mo–V alloy are studied. A fine α/β lamellar microstructure is obtained. High-cycle fatigue test was conducted at room temperature. Fatigue fracture surfaces are examined by SEM. Fatigue crack initiates by cleavage fracture along crystallographic facets in α and propagates by cleavage facets and tearing of α/β lamellar colonies in fatigue crack initiation region. At applied stress less than 750 MPa, fatigue crack nucleation is characterized by the crystallographic cleavage facets of α lamellae and tearing of β lamellae. Striations are observed parallel or perpendicular to the lamellar orientation. Two types of steps are observed in the crack propagation. The mechanisms of fatigue nucleation and growth in laser deposited Ti–6Al–2Zr–Mo–V alloy are related to the slip behaviors and the interactions between crack and colony boundaries.