High-Strain-Rate Deformation of Ti-6Al-4V Through Compression Kolsky Bar at High Temperatures

In this paper, we present our first results from the study of the constitutive response of a popular Titanium alloy, Ti-6Al-4V, using a variation of the compression Kolsky Bar technique that employs electrical pulses to achieve high temperatures. Experiments are conducted at temperatures ranging from room temperature to 1000 degrees C at a strain rate of about 2200 s(-1) and a heating rate of about 1500 degrees C/s. The dynamic stress-strain results demonstrate significant thermal softening in the alloy that could be described by Johnson-Cook equation with m - 0.8 up to 650 degrees C. Above 650 degrees C the rate of change in the flow stresses was faster, which is attributed to allotropic transformation that results in a change in the phase fractions of the hcp and bcc phases present in the alloy. Evidence of transformation is observed in the microstructure of post-compression specimens, which showed an acicular morphology formed from the high temperature bcc phase on quenching.