Experimental and atomic observations of phase transformations in shock-compressed single-crystal Fe

Abstract

The phase transformations in Fe have been of technological and sociological importance in the development of human civilization. The α→ε (BCC→HCP) martensitic transformation is the best known phase transformation of Fe and has been extensively studied. However, the mechanisms of α→ε and ε→α transformation upon shock loading and release are not yet understood owing to its short life and reversibility. In this study, we designed experimental and atomic methods for observing the shock-induced phase transformations in [001] and [111] single-crystal Fe, using shock recovery experiments and molecular dynamic simulations. It was found that the orientation relationships in the [001] and [111] single-crystal Fe are consistent with previously proposed transformation mechanisms. The α→ε transformation was attributed to the (110) slip system, while the reverse transformation was attributed to the (112) slip system. Furthermore, it was postulated that the rod-like microstructures observed in the shock-recovered samples were caused by the wave interactions during the unloading. However, the rod-like shapes in the [001] Fe were caused by the activation of dislocations in the b1 = ka[11–2] and b2 = ka[112] Burgers vectors. Only the b3 = ka[112] dislocation was activated in the [111] Fe sample.