Microscopic crack propagation mechanism and fatigue crack growth behavior of Ti-5321 alloy formed by laser cladding

Abstract

To satisfy the need for rapid production of high damage tolerance titanium alloys in the aerospace industry, Ti-5321 alloy was manufactured using laser cladding. Single annealing and BASCA (β annealed, slow cooled, and aged) of the Ti-5321 alloy produced two distinct microstructures: basket-weave structure and large layer structure. Their influence on fatigue crack propagation was investigated. The results indicate that: basket-weave structure, comprised of elongated lamellar α, exhibits excellent plasticity and toughness. There was significant orientation difference between adjacent lamellar α, and multiple slip may occur during the slip process. The microscopic fracture propagation pattern of basket-weave structure resembled a "sawtooth", signifying a high resistance to crack propagation and a robust capacity to inhibit propagation. Large layer structure consisted of large lamellar α on a scale of 10–30 μm and ultrafine needle-like α. It possesses an exceptionally high ultimate tensile strength of 1300 MPa and a low toughness of 46.0 MPa·m^1/2. The orientation difference between adjacent α/β was minimal and susceptible to single pyramidal {10−11}< 1–210 > slip. The microscopic crack propagation pattern of large layer structure resembled little "steps". These factors have resulted in diminished crack propagation resistance.