Transient phase transitions in single-crystal coppers under ultrafast lasers induced shock compression: A molecular dynamics study

Transient phase transitions in ⟨100⟩-oriented monocrystal coppers under ultrafast lasers induced shock compression are investigated using molecular dynamics simulation. Due to propagations and attenuations of compressive stress waves induced by ultrafast laser pulses, monocrystal coppers show distinct processes of structural phase transitions, i.e., first, face-centered cubic (FCC) → body-centered cubic (BCC), then BCC → FCC, then FCC → hexagonal close-packed (HCP), and finally some of HCP → FCC. The known Bain's phase transition path of FCC → BCC in copper is discussed in detail and the mechanisms are disclosed by using the modified Born stability criteria and the local minimum energy criterion. By considering the initiation of stacking faults, the mechanism of phase transition of FCC → HCP is well explained. Through the analysis of phonon spectra, the results show that both BCC and HCP phases are unstable phases of monocrystal coppers.