Phase-field modeling of alloy oxidation at high temperatures

Oxide growth is a complex process involving transport of reactive species, heterogeneous reactions, and microstructure evolution. Predicting oxidation kinetics, especially the oxide morphological change has been a longstanding challenge. Here we develop a phase-field model for predicting the oxide growth kinetics of a multicomponent alloy during high temperature oxidation, focusing on internal oxidation (non-protective) and its transition to external oxidation (protective). The predicted kinetics and oxide morphology are analyzed and compared to the classical Wagner's theory and an existing analytical model by Zhao and Gleeson. Some assumptions used in the analytical models and the limitation are discussed. In addition, it is demonstrated that the morphology and distribution of the initial oxide nuclei play an important role in the later stage oxide connectivity and thus the transition to external oxidation.