Tight-binding quantum chemical molecular dynamics (QCMD) were applied in order to study the random grain boundary oxidation mechanism of an Fe-Cr binary alloy in a boiling water reactor (BWR) environment. The metal-water interaction at high temperatures causes diffusion of environmental species and segregation of metallic atoms. Water molecules favorably permeate through the grain boundaries in order to find the space generated by atomic rearrangement, although it is difficult to diffuse in the perfect lattice. The dissociated oxygen and OH concentrations increase around the chromium and preferentially bind to the metal to initiate passive film formation at the elementary stage. Moreover, applied strain creates extra spaces in the lattice that can facilitate the absorption of environmental species. In order to enhance the diffusivity of water molecules, OH, O and H produce an atomic void on the surface that can assist with further penetration of environmental species. Mulliken population analysis shows that the highly positive charge of chromium and the negatively charged oxygen atoms or OH remain along the grain boundary by forming bonds. The grain boundary atoms selectively lose their valence electrons when water molecules adsorb, indicating that the oxidation process is a possible mechanism of intergranular stress corrosion cracking initiation.
ASJC Scopus subject areas
- 化学 (全般)