Microscopic studies of structural transition in iron under one-dimensional strain

Molecular dynamics simulation employing an embedded-atom-method potential is performed to investigate the body-centered cubic (bcc)-hexagonal close-packed (hcp) structural transition in single crystal iron induced by isothermal compression along [001] direction. Above the critical strain of transition, homogeneous nucleation of hcp phase appears and grows into flakes along the (011) face. The elastic constants C₃₁ and C₃₂ harden during the compression in bcc phase, while C₃₃ undergoes a softening prior to the transition; all the elastic constants increase rapidly with compression after the system entering the hcp phase. Increasing temperature can weaken the hardening and softening process of C₃₃, but affect the stress threshold of transition only weakly. Hcp twins are formed at 300 K, leading to the shear of crystal lattice. For the mixed phase, the potential of hcp phase is greater than that of bcc phase, hcp phase shows an over-relaxation of the stress, and the longitudinal partial stress keeps linearly decreasing with hcp mass fraction throughout the transition.