Atomic Insight Into Phase Transition Lowering in Shock Compressed Copper

Abstract

High pressure structural transformation of copper (Cu) is a rather complex physical process. One of the intriguing questions that are rarely discussed is the comparison between quasi-isentropic response and adiabatic response for copper lattice transition. The ambient face-centered-cubic structure of Cu is predicted to persist over 100 TPa from ab inito calculations and experimentally demonstrated to persist until 1.15 TPa in ramp compression and 150 GPa in static compression. However, a novel body-centered-cubic (BCC) order is observed merely at 180 GPa once shock compression is applied. The mechanism of body-centered-cubic phase transition occurred at low pressure under shock compression remains elusive so far and much attention is required on the dynamics in such a phase transition. In this work, we utilize the molecular dynamics method to simulate the shock compression on a copper lattice to uncover the structural transition in the atomic scale. We report the FCC–BCC phase transition occurred at 156 GPa, and lots of disordered structures are discovered in the BCC phase after impact, revealed by a series of structure analysis tools and free energy calculations. The plethora of transient disordered structures reduces the global Gibbs free energies, thus leading to the downgrade of the transition pressure in contrast to the ramp and static compression, which provides a new perspective for structural transformation under extreme conditions.

Noncovalent Interactions in Mechanical Response of Thermoset Epoxy Resin

“…The MSST is typically used to probe the structure of a system at longer time scales after shock equilibration and cannot be used to probe the nonlinear changes to the system at different time instants of shock propagation. The MSST algorithm has been previously utilized by the research community for various metals like Cu and Al as well as polymers like polyethylene, polyurethane, polyurea, and polystyrene. ,− No profound drift in energy, in terms of departure from the Hugoniot line (in the temperature unit) and the Rayleigh line (in the pressure unit), has been observed within the time scale of the simulation. In the current simulation, the time instant chosen to probe the equilibrated system after shocking the medium is 2 ns.…”

The thermodynamic-pathway-determined microstructure evolution of copper under shock compression

“…Nonetheless, recent laser shock compression experiments have revealed that copper undergoes a phase transition from FCC to body-centred cubic (BCC) at pressures around 180 GPa [17], significantly below the theoretical prediction [18]. This phase transition is thought to result from the generation of stacking faults [17] or transient disordered structures [19] under shock compression. The shock process involves coupling thermodynamic quantities, such as pressure and temperature, with microstructural alterations, indicating the need for a more comprehensive study of dynamic processes at both temporal and spatial scales.…”