Fracture toughness of Ti–22Al–25Nb alloy at room and high temperatures

In this research, the fracture toughness of Ti–22Al–25Nb orthorhombic alloy with bimodal size lamellar O phase microstructures was investigated at room temperature and 650 °C. In addition, the fracture toughness model and crack tip plastic zone model were established by simplifying the shape of the crack tip plastic zone. The fracture toughness model is used to quantitatively calculate the intrinsic and extrinsic contributions to fracture toughness, and the crack tip plastic zone model is used to calculate the real height of the crack tip plastic zone. The results show that the fracture toughness K_IC at high temperature is twice that at room temperature. The fracture mechanisms at room and high temperatures are the quasi-cleavage fracture and dimple fracture, respectively. The increase of temperature is conducive to the significant increase of the fracture toughness by improving the inherent property of the material (intrinsic contribution) and the crack propagation tortuosity (extrinsic contribution). The fracture toughness at room temperature is dominated by intrinsic contribution while the fracture toughness at high temperature is dominated by both the intrinsic and extrinsic contributions. Besides, whether at room temperature or high temperature, the intrinsic contribution is the most important factor to the total fracture toughness. The increase of temperature significantly improves the size of the crack tip plastic zone, which leads to a significant increase in fracture toughness.