Atomic-scale simulation of α/γ-iron phase boundary affecting crack propagation using molecular dynamics method

Phase boundaries play significant roles in the crack initiation and propagation behavior of duplex phase materials such as nanoscale bainite–austenite (α/γ) microstructures. Simulation of α/γ-iron phase boundary interacting with crack propagation was carried out using molecular dynamics method. Bi-phase systems consisting of α-iron with body-centered cubic structure and γ-iron with face-centered cubic structure, were constructed. Phase boundaries were created using Nishiyama–Wasserman and Kurdjumov–Saches (K–S) orientation relationships, respectively. Eight orientations of cracks in α- or γ-phase were analyzed to illustrate the orientation dependence of crack growth. Finnis–Sinclair potential for Fe fit by Mendelev was used to describe interatomic potentials. Tensile load was applied normal to the crack surface. Simulation results reveal that in most cases phase boundary provides an obstacle to slip and dislocation motion during crack propagation, except in two orientations with K–S relation. New-cracks always nucleate phase boundary as a result of slip blocking and dislocation pileups. Bcc/fcc iron phase boundary is therefore demonstrated to be a great contribution to the strengthening of nanoscale duplex steel.