Dynamic X-ray Diffraction to examine the Shock-Induced Phase Transitions and Melting in Cerium Metal

There is a scientific need to understand the dynamic response of materials at extreme conditions which is relevant for the understanding of phenomena related to condensed matter physics, general solid flow behavior, and planetary science. Dynamic experiments are needed to locate phase boundaries, to obtain equation-of-state information on pure phases, and to understand the evolution of the microstructure during loading. Cerium is ideal for such studies because it exhibits a rich phase diagram that includes four solid phase at zero pressure, additional solid phases at high pressure, and an anomalous melt boundary. Of particular interest to the current work is the well-known isostructural (γ-α) phase transition that occurs at low-pressures. This boundary terminates in the solid phase at a critical point and is accompanied by a large volume collapse that leads to a low-pressure melt transition at approximately 10.2 GPa. The current work takes advantage of this low-pressure melt transition to use dynamic X-ray diffraction to study shock melting of metals. XRD data were obtained for impact stresses that spanned the melt transition which provided information on the high pressure phase pointing toward a complete melt transition near 16 GPa.