Modeling the Shock-induced Phase Transformation Behavior in Fe microstructures at the Atomic Scales and Mesoscales

Shock compression of Fe microstructures above threshold pressures results in a BCC to HCP phase transformation. MD simulations are carried out to investigate the role of loading orientations and shock pressures above the thresholds of phase transformation and identify the correlations between loading orientations, and shock pressures using MD simulations, and unravel the conditions of reverse transformation induced twinning during shock release in single-crystal microstructures. To model the shock response of polycrystalline microstructures, a novel mesoscale modeling method, Quasi-Coarse-Grained Dynamics (QCGD), is used to extend the study to experimental scales with grain sizes of up to a few microns. The QCGD method retains the atomistic mechanism of dislocation slip, twinning, and phase transformation as predicted using MD simulations. The phase transformation and twinning variants in the atomic scale and mesoscale microstructures are characterized using orientation matrix and angle/axis pair from virtual texture analysis at different stages of shock evolution. MD and QCGD simulations reveal that Fe oriented along [110] direction is prone to twin. The talk will discuss the mechanisms of the formation of various HCP variants during shock compression and the mechanisms of reverse transformation and twinning during shock release to identify the role of loading orientations and shock pressures using MD and QCGD simulations.