High-temperature deformation behaviour of Ti6Al4V alloy evaluated by high strain-rate compression tests

The high-temperature deformation behaviour of Ti6Al4V alloy has been investigated using the split Hopkinson bar. The specimens were deformed under a constant strain-rate of 2 x 10(3) s(-1) at an initial temperature varying from 700-1100 degrees C at intervals of 100 degrees C. In order to compare the effect of temperature on the flow characteristics, room-temperature tests were also performed to determine the basic mechanical properties. Parallel with this work, the fracture features and microstructures of the deformed specimens were studied by means of different microscopy techniques to understand the formation of adiabatic shear bands and the variations of dislocation features. In addition, for the purpose of describing the flow behaviour of this material in terms of strain, strain rate and temperature, a deformation constitutive equation is proposed. The present results demonstrate that temperature has a significant effect on the flow behaviour of the material. The strength of the material and the work-hardening coefficient decrease rapidly with an increase in temperature. Furthermore, the proposed constitutive equation describes and predicts excellently the observed flow response. From the fracture analysis localized adiabatic shearing forming due to impact is found to be favoured with Ti6Al4V alloy and increases with increasing temperature of deformation. Microstructural observations show that dislocation cells form under all conditions, and that the dislocation density and cell size vary with the temperature. A quantitative relationship between the flow stress and observed dislocation structure is characterized. (C) 1998 Elsevier Science S.A.