Vacancy-Creep Model for EAC of Metallic Materials in High Temperature Water

A new mechanistic model for environmentally assisted cracking (EAC) of metallic materials is presented. In this model the mechanism of cracking involves selective dissolution or oxidation of metallic cations in the oxide film and transport of the generated vacancies to the base metal ahead of the crack tip. The mechanism of cracking is based on interactions of vacancies with dislocations enhancing concentration of slip to the highly stressed region ahead of the crack tip. The validity of the model is discussed based on both new experimental and literature data. It is shown that selective oxidation and, thus, vacancy generation takes place in the same electrochemical potential range where EAC cracking is observed at different temperatures in different materials such as in stainless steels, Ni-base alloys and brass. This model can be applied to explain the observed transgranular stress corrosion cracking (TGSCC), intergranular stress corrosion cracking (IGSCC) and hydrogen embrittlement (HE) phenomena of these materials used in high temperature water environments.