The influence of peak shock stress on the high pressure phase transformation in zirconium

At high pressures zirconium is known to undergo a phase transformation from the hexagonal close packed (HCP) alpha phase to the simple hexagonal omega phase. Under conditions of shock loading, the high-pressure omega phase is retained upon release. However, the hysteresis in this transformation is not well represented by equilibrium phase diagrams and currently models that accurately represent such a solid-solid phase transformation coupled with the multi-phase plasticity likely under shock conditions do not exist. For this reason, the influence of peak shock stress on the retention of omega phase in Zr is explored in this study. In-situ VISAR measurements along with post-mortem metallographic and neutron diffraction characterization of soft recovered specimens have been utilized to quantify the volume fraction of retained omega phase, morphology of the shocked alpha and omega phases, and qualitatively understand the kinetics of this transformation. This understanding of the role of peak shock stress will be utilized to address physics to be encoded in our present macro-scale models