Atomistic simulation of stress-induced phase transformation and recrystallization at the crack tip in bcc iron

The mechanisms of low-temperature deformation at the crack tip in body-centered cubic (bcc) iron have been studied by molecular dynamics simulations. Phase transformation and recrystallization are found to occur at the crack tip when a sufficiently high stress concentration exists. The mechanisms of new grain nucleation and phase transformation in particular are discussed. For {1 1 0}〈1 1 0〉 and {1 11}〈1 1 0〉 cracks, phase transformation from the bcc structure to a typical close-packed hexagonal structure is observed accompanying new grain nucleation at the crack tip. It is found to be achieved by the emission of 16〈111〉 partial dislocations on the {1 1 2} slip plane. For the {1 0 0}〈1 1 0〉 crack, two long twin strips appear at the crack tip along the 〈1 1 1〉 slip direction. A new grain with a different orientation from the original bcc crystal is formed with the growth of the twin region.