Intrinsic characteristics of grain boundary elimination induced by plastic deformation in front of intergranular microcracks in bcc iron

Abstract

Additive grain boundary (GB) engineering holds significant potential for developing materials and structures with excellent mechanical properties by precisely controlling GB structure. The GBs that can be eliminated by plastic behavior activities prior to crack cleavage are ideal special ones for resisting intergranular fracture. Through molecular dynamics simulation, this work constructs special boundaries and studies the intrinsic characteristics of GB elimination. The results show that GB elimination phenomenon significantly depends on crack growth direction and GB plane. The classical theory developed by Rice fails to identify the mechanisms of two dependent characteristics. According to shear forces on atoms at crack tip, this work finds that the dependence of GB elimination on crack growth direction is attributed to the change of atomic slip characteristics. GB elimination occurs in specific growth directions where atomic slip is driven by the system of $\left(1\overline{1}2\right)\left[\overline{1}11\right]$. By considering T stress effect, GB elimination and its dependence on GB plane are well explained. The dependence of GB elimination on GB plane is attributed to the complex changes in critical stress intensity factors for twinning formation, perfect dislocation nucleation, and cleavage. GB elimination occurs on specific GBs where T stress makes the critical stress intensity factors for twinning and dislocation nucleation significantly lower than that for cleavage. The identified intrinsic characteristics of GB elimination provide references for GB design.