Effect of annealing temperature on the microstructures and impact toughness of Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy plates

Abstract Numerous studies have clarified the importance of measuring the impact toughness of titanium alloy drill pipe, however, the influence of heat treatment parameters on the impact toughness of titanium alloy is seldom discussed. Herein, the influence of annealing temperature on notch impact toughness of Ti-6Al-4V-0.5Ni-0.5Nb alloy was investigated by Charpy impact test. Optical microscope and SEM characterized the impact specimens’ annealing microstructure and fracture surface. The results revealed that the primary α phase gradually decreases with increasing annealing temperature, and the impact toughness of the plate increases first and then decreases. The alloy fracture changes from quasi-cleavage fracture to ductile fracture, and with the temperature rising to the phase transformation point, the fracture of the alloy mainly turns into cleavage fracture.