Microstructure Characteristic and Fatigue Crack Propagation Behavior of Ti-5321 Alloy Formed by Laser Cladding

In order to meet the demand for rapid preparation of high damage tolerance titanium alloys in the aerospace field, Ti-5321 alloy was fabricated by laser cladding. Through single annealing and multiple heat treatments (holding at 880 ℃ for 1 h, cooling to 800 ℃ at the furnace cooling rate of 0.5 ℃/min, then air cooling to the room temperature, finally aging at 580 ℃ for 6 h/AC) of Ti-5321 alloy, the microstructure evolution and its impact on fatigue crack growth were explored. The results show that: after single annealing, the morphology was basket-weave structure, which composed of elongated α lamellar. For basket-weave structure, a variety of slip occurs during the crack propagation process due to the large orientation difference between adjacent α lamellar. Therefore, this will significantly increase the crack growth resistance, as well as, the tortuosity of the crack growth path. After the multiple heat treatments, prior α transforms into large α lamellar in 10~30 μm scale and ultrafine needle-like α, resulting in an increased strength but decreased plasticity and toughness. In micro structures with large α lamellar, the orientation difference between adjacent α lamellar or α/β was extremely small. In this case, the basal slip was prone to occur, leading to the weaker crack propagation resistance, which decays the damage the performance of fatigue crack propagation resistance of the alloy.