Study on phase transformation in Tin under dynamic compression

Abstract

We propose to study experimentally the polymorphic transition of Tin under dynamic compression. These transformations have been investigated for a long time through usual velocity measurements under shock from ambient condition. At CEA Gramat we have improved our understanding of such phase transformations through both experimental and theoretical means. Experimental velocity measurements have long suggested that non equilibrium behavior and kinetics is an important part of the dynamic compression response of materials undergoing phase transformations. Empirical kinetic models can in many cases reproduce the experimental velocity profiles, but without clearly identifying the nature of the transition. For nearly two decades, the CEA Gramat operates several gas guns for shock loading and high pulsed power (HPP) drivers dedicated to Isentropic Compression Experiments (ICE) up to several GPa. These experimental devices and associated diagnostics (velocimetry and temperature measurements and x-ray diffraction experiments) help to begin to study kinetics under dynamic transition in a more rigorous manner. We have used these experiments to examine various compression paths and have used the results to improve equation of state (EOS) models incorporated in our numerical codes. The latter can be used to run simulations starting with ambient initial conditions, then load metallic materials from various non ambient initial temperatures. This can significantly extend the range of our studies into previously unexplored thermodynamic paths. We propose to describe our preheating devices for gas gun experiments and our HPP driver, and to present our preliminary results on shock loading and on isentropic compression at various initial temperatures, to explore the phase diagram of Tin. In addition, we present the design of promising testing on X-ray diffraction under shock to help to develop a more physical kinetic model relying on nucleation and growth mechanisms, which are implemented in our continuum level codes.