Multiple phase transitions in shock compressed high-entropy alloy Cr9Mn9Fe64Co9Ni9: Experiments and molecular dynamics simulations

Dynamic response of a non-equiatomic high-entropy alloy, Cr9Mn9Fe64Co9Ni9, to shock compression is investigated via plate impact along with in situ free surface velocity measurements. Postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. After shock compression, microstructure characterizations reveal shock-induced stacking faults, the Lomer–Cottrell dislocation locks, nanotwins, and the face-centered cubic (FCC) to hexagonal close-packed (HCP) and FCC to body-centered cubic (BCC) transitions. The HCP and BCC phases follow Shoji–Nishiyama and Kurdyumov–Sachs orientation relations with the FCC matrix, respectively. Large-scale molecular dynamics simulations are conducted to illustrate the phase transition mechanisms. The BCC phase can form via the FCC–HCP–BCC path.