Direct approaches to distinguishing deformation and phase transformation structures in shock-loaded iron

Abstract

An α-Fe → ε-Fe phase transformation occurs in iron when the shock loading pressure exceeds 13 GPa, but all the ε-Fe will reverse back to α-Fe during unloading, resulting in no residual ε-Fe in the unloaded samples. To prove the occurrence of this process, a series of microstructural characterization techniques were used to study the microstructures of shock-loaded iron, but hard to reach a consensus on the experimental results. Here, by using two conventional electron microscopy techniques, electron backscattered diffraction (EBSD) in scanning electron microscopy and selected area electron diffraction (SAED) in transmission electron microscopy, we reveal six novel phase transformation variants directly related to the reversible phase transformation. On this basis, the essential differences of microstructure between deformation area and phase transformation area are revealed. Further, we propose two fast and efficient methods which can identify the occurrence of the reversible phase transformation by EBSD and SAED, respectively. The universality of these methods has been verified in different shock loading experiments in iron. • The differences of microstructure between deformation area and phase transformation area in shock-loaded iron are revealed. • The characteristic microstructures of phase transformation are investigated. • The method of identifying the occurrence of phase transformation by EBSD is developed. • The diffraction pattern of all characteristic structures for SAED is drawn.