Shock wave determination of temperature dependence of twinning stress in vanadium and tantalum

Abstract

The temperature dependencies of twinning stress τtw in pure polycrystalline BCC vanadium and tantalum were established using shock wave approach based on two types of shock wave experiments. In the tests of the first type, relatively thick samples were softly recovered after planar impact loading and underwent metallographic examination for determination of twin density Ntw(h) (number of twins per unit area) variation as a function of distance h from the impacted sample surface. In the impact tests of the second type, variation of the shear stress with h, τ(h), was studied with the samples of the same metal of different thickness. The latter, being combined with Ntw(h), allows determination of Ntw(τ) and of the shear stress τtw at which Ntw becomes equal to zero. Varying initial sample temperature T made it possible to establish temperature dependencies τtw(T) over 300–700 and 300–800 K temperature ranges for vanadium and tantalum, respectively. The relation of the obtained results with possible scheme of twins nucleation and growth is discussed.