Influence of Deformation Parameters on Fracture Mechanism of Ti40 Titanium Alloy

An important concern in forming is whether the desired deformation can be accomplished without cracking or fracture of the work material. In this research, based on the cracking specimens obtained from hot compression experiment, the fracture behavior of as-cast highly β stabilized Ti40 alloy was investigated at the deformation temperatures of 1123~1373 K, strain rates of 0.01~10 s^-1 and height reduction of 70%. The main fracture modes consist of 45^o shear fracture and longitudinal cracking occurring on free-surface, as well as inner cracking occurring at the triple boundary junctions. Moreover, the influence of deformation parameters on fracture mechanism was analyzed emphatically in terms of SEM. At low temperature of 1123 K the transgranular cleavage brittle fracture is observed; at 1273 K the ductile fracture occurs; at high temperature of 1373 K a lot of small dimples on the fracture interface are examined. Furthermore, the effect of strain rate on the fracture behavior of as-cast Ti40 alloy is significant. At 0.01 s^-1, the fracture des not occur. At the strain rates of 0.1 and 1 s^-1, the fracture surface is covered with a large amount of dimples indicating that the fracture mode is ductile fracture, while at high strain rate of 10 s^-1, the fracture surface shows a brittle fracture feature. Finally, the damage mechanism and fracture reason were discussed and fracture principle diagram was drawn for the as-cast Ti40 titanium alloy.