Resistance of fatigue crack propagation induced by large α colony in a Ti‐Al‐V‐Mo‐Zr alloy

Abstract For Ti alloys used in oil drilling pipe, the fatigue crack propagation (FCP) resistance is one of the key properties for petroleum industrial applications. In this work, the fatigue crack propagation behaviors of bimodal, equiaxed, lamellar, and Widmanstatten microstructures have been systematically investigated and characterized by SEM and EBSD. The results show that the Widmanstatten microstructure containing α colonies has higher yield strength (877 MPa), moderate elongation (9.3%), and better FCP resistance compared to other specimens. During the process of crack propagation, the large α colonies can effectively deflect the cracks and induce secondary cracks, which significantly impedes the main crack propagation. Additionally, tensile twinning can occasionally occur within the large α colony along the crack, improving the plasticity of the crack tip and resulting in a decrease in fatigue crack propagation rate (FCPR).