The interrelation of crack propagation behaviors and lamellar structure in a new near α titanium alloy at low temperature

Abstract

In this work, crack propagation behaviors and fracture mechanism of CT20 alloy with lamellar α at the temperatures ranging from 20 to − 90 °C were investigated and revealed. The results showed the fracture toughness of CT20 alloy was decreased from 430.89 KJ/m2 to 171.67 KJ/m2, and the fracture mechanism was gradually changed from typical ductile fracture to quasi-cleavage fracture with the decreasing testing temperature. The reduction of fracture toughness was mainly influenced by the internal factor (the crack tip plastic zone) and external factor (the tortuosity of the crack propagation path), in which the contribution of the internal factor increased from 87.06% to 95.68% as the temperature decreased. Therefore, the high contribution of the internal factor means the plastic zone at the crack tip could mainly affect the crack propagation behaviors. The lamellar α was found to be deformed by the plastic zone, and then inhibited the crack propagation and deflected its propagation direction at 20 °C, which consumed the additional deformation energy and increased the fracture toughness. With the decline of the plastic zone from 0.526 mm to 0.107 mm, the lamellar α deformation and the crack propagation resistance were significantly reduced at − 90 °C, which accelerated crack propagation and decreased the fracture toughness.