Optical measurements of phase transition and temperature in adiabatic shear bands in titanium alloys

Abstract
Adiabatic shear bands may occur in different type of solicitation such as high speed torsion, compression, and ballistic impact. The formation of a shear band is often an immediate precursor to rupture of the material. Fast localised temperature's gradient results from this plastic deformation. In order to generate adiabatic shear bands, we have built a dynamic punching device. We determine the temperature and the transition phase by optical measurement. A measure at two wavelengths allows us to dissociate the temperature and the emissivity. A measure at 6 µm leads to the temperature in shear band and a measure at 5 µm leads to the emissivity variation of the material and allows to identify the phase transition. The experimental results obtained for TA6V have enabled us to point out the existence of very high temperatures (T_max 1273 °C) within the shear band. We compare the emissivity variation of two titanium alloys (The TA6V and the Ti20V) and we detect the α → β phase transition in the case of the TA6V alloy.