Orientation Dependent Quasi-isentropic Tensile Behaviors of Body-Centered Cubic Tungsten Through Molecular Dynamics

In this study, dynamic mechanical response and the corresponding atomic mechanisms of single-crystal tungsten under extreme strain rates (109 s−1) are investigated using molecular dynamics simulations. The results show that crystal orientation plays an important role in the stress–strain relationship. The critical stresses for the beginning of plastic deformation are 59.4, 48.0, and 25.2 GPa for quasi-isentropic tensile loading along [111], [110], and [100] crystal orientations, respectively. The atomic behavior during plastic deformation suggests that [100] and [110] experience stress relaxation through phase transitions, while not in the [111] tensile direction. During spallation, sub-grain boundaries formed at twin junction in the [100] and [110] directions serve as nucleation sites for voids. The void grows in a planar way (along the twin) after generation, while stops growing at another misoriented twin junction. In the [111] tensile test, spallation occurs in the stress-concentration area, and finishes in a very short time interval with huge void coalescence. Our findings not only provide atomic insights into the anisotropic mechanical behaviors during spallation of tungsten under high strain rates, but also shed lights on the colorful plastic deformation behaviors from laser-shock experimental observation.