Effects of strain rate and temperature on the deformation and fracture behaviour of titanium alloy

The deformation response and fracture behaviour of Ti alloy under strain rates of 8 x 102 S-1 to 8 X 10(3) s(-1) at temperatures ranging from 25 degrees C to 900 degrees C are studied using split-Hopkinson pressure bar. The mechanical properties and fracture features of the alloy are found to be significantly dependent on both the strain rate and the temperature. At a constant temperature, the flow stress increases with increasing strain rate. However, at a given strain rate, the flow stress reduces as the temperature increases. Furthermore, the fracture strain decreases with increasing temperature prior to phase transformation at 785 degrees C, but increases thereafter as the temperature is further increased. As the strain rate increases, the strain rate sensitivity increases, but the activation volume decreases. However, as the temperature increases, the strain rate sensitivity decreases and the activation volume increases. Optical microscopy (OM) and scanning electron microscopy (SEM) observations reveal that the alloy specimens fracture primarily as the result of the formation of adiabatic shear bands. The fracture surfaces of the impacted specimens exhibit both dimple-like and cleavage-like features. The density of the dimples reflects the toughness of the alloy specimen and is found to vary directly as a function of the strain rate and the temperature.