The dynamic response of a β titanium alloy to high strain rates and elevated temperatures

Abstract

The stress–strain behaviour and microstructural evolution of the Ti–6Cr–5Mo–5V–4Al (Ti6554) alloy was systematically investigated using Split Hopkinson Pressure Bar (SHPB) tests over a wide range of strain rates from 1000s−1 to 10,000s−1 and initial temperatures from 293K to 1173K. Dislocation slip is the main deformation mechanism for plastic flow of the Ti6554 alloy at high strain rates. The flow stress increases with increasing strain rate and decreasing temperature. Also the flow stress is more sensitive to temperature than to strain rate. For high strain rate deformations, the strain hardening rate is found to be negative at 293K and increases with increasing temperatures. Flow softening observed at 293K is potentially caused by adiabatic heating. The increment in the strain hardening rate with increasing temperatures may be the result of interactions between thermally activated solute Cr atoms and mobile dislocations. When the temperature is raised to 873K, a novel α precipitate morphology consisting of globular α aligned in strings was observed in specimens deformed at strain rates of 4000 and 10,000s−1. It has hardening effects on the β matrix and is purported to nucleate on dislocations introduced by the high strain rate deformation. Adiabatic shear bands were observed in specimens deformed at higher temperatures (873K). The microstructure inside the shear bands is harder than that outside of the shear bands in the Ti6554 alloy.