Experimental and theoretical examination of shock-compressed copper through the fcc to bcc to melt phase transitions

Recent studies show a face-centered cubic (fcc) to body-centered cubic (bcc) transformation along the shock Hugoniot for several metals (i.e., Cu, Au, and Ag). In this study, we combine an experimental and theoretical approach to examine this transition. We completed laser-shock compression on Cu foils at nanosecond timescales with in situ X-ray diffraction (XRD) to examine the microstructural changes with stress. We study the changes within the fcc phase, the phase transition from fcc to bcc (pressures greater than 180 GPa), and the bcc phase. Textural analysis of the azimuthal intensities from the XRD images is consistent with transformation into the bcc phase through the Pitsch-distortion mechanism. We use embedded atom model molecular dynamics simulations to determine the stability of the bcc phase in pressure-temperature space. Our results indicate that the bcc phase is stabilized only at high-temperatures, and it remains stable at pressures greater than 500 GPa.