| A comparison of microstructures associated with W single-crystal ([001], [011], [111]) rods prior to deformation (as grown), and after quasi-static compression (at a strain rate of ∼1/s) by transmission electron microscopy (TEM) shows several orders of magnitude difference in dislocation density. Dislocation substructures were not significantly different amongst the deformed sample orientations, except for that of [011]; the presence of deformation bands seen optically and by TEM was unique to this sample. In contrast, [001] W rods penetrated into steel targets, at impact velocities of ∼1.3 km/s, exhibited heavy dislocation densities, sub-grains, and dynamic recrystallization as very distinct microstructural regimes accommodating the penetration process. Twinning on {lcub}112{rcub} also occurred as a precursor to, or remnant of, these microstructures near the projectile head. These results demonstrate that deformation accommodating the extreme strains and strain rates associated with the penetration of a single-crystal rod into a metal target is not adequately represented by conventional deformation mechanisms. |
