Strain rate dependence of deformation twinning in Ta

Abstract

Large-scale non-equilibrium molecular dynamics (NEMD) simulations are used to examine the role of dislocation density and strain rate on twin nucleation and deformation twinning in tantalum. The initial dislocation density was varied between 1011 − 1012 cm−2. The samples were compressed quasi-isentropically to pressures up to 100 GPa, at strain-rates in the 108 − 1012 s−1 range. The twin volume fraction, dislocation density and peak shear stress were evaluated as a function of strain and strain rate. Main results indicate that at these high strain rates, twinning in tantalum is strongly dependent on the dislocation density and strain (pressure). Deformation twinning, as measured by the twin volume fraction (TVF), increases with increase in strain rate for strain rates > 109 s−1. Below this value, a small fraction of twins nucleates but anneal out with time. Samples with lower fraction of twins equilibrate to defect states containing higher dislocation densities from those with initially higher twin volume fractions.