[SY-K4] Molecular Dynamics Simulation on Intergranular Cracking Mechanism of Iron Material in High Temperature Pressurized Water Environment
Iron-based materials are widely used in power plants, and usually serve in high temperature pressurized water environment. The severe water environment causes stress corrosion cracking (SCC), resulting in potentinally catastrophic accidents. It is therefore important to understand the chemical reaction dynamics at the iron-water interface and the SCC mechanism during failure process in order to improve corrosion resistance. However, it is difficult to achieve that by experimental observation, particularly in high temperature pressurized water. Thus, the SCC mechanism for iron-based materials in such an environment is still unclear. In this study, we employed molecular dynamics simulation to study the failure process in high temperature pressurized water environment. To investigate chemical reactions, a reactive force field was used in this study. Since intergranular cracking is more common than transgranular cracking during the fracture processes of iron materials, a Σ5(310) grain boundary was modeled. To investigate the crack growth process under stress conditions, we applied external tension along the perpendicular direction of the pre-crack model with water arranged on the surface. The simulation results showed structural change due to plastic deformation around the pre-crack, and the structural change was found to be attributable to twinning by partial dislocations. In addition, small cracks were observed in the lateral direction of the pre-crack tip. To investigate the effect of high temperature pressurized water, we also simulated the model without water for comparison. It was revealed that crack propagation was promoted by suppressing structural relaxation due to the chemical reactions in the high temperature pressurized water condition.