High-strain-rate deformation of TI-6AL-4V through compression Kolsky Bar at high temperatures

Abstract

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 °C at a strain rate of about 2200 s-1 and a heating rate of about 1500 °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 °C. Above 650 °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 postcompression specimens, which showed an acicular morphology formed from the high temperature bcc phase on quenching.