Modeling of θ → α alumina lateral phase transformation with applications to oxidation kinetics of NiAl-based alloys

Abstract

In the present work, a physical model has been developed to predict the growth of Al2O3 scale, which involves the thickening of metastable transient θ-Al2O3 phase and finally thermodynamically stable α-Al2O3 phase, accompanied by the concurrent θ→α-Al2O3 phase transformation. Based on nucleation and growth theory, the phase transition kinetics and alumina growth were modeled for both isothermal and continuous heating paths. Using this model, the phase transformation kinetics, evolution of grain size and Al2O3 scale thickness can be predicted for a given thermal path. A new scaling parameter has been proposed that quantitatively reveals the relative significance of nucleation and grain growth to the overall phase transformation kinetics. Predictions based on the model are in good agreement with the experimental observations. Limitations of the model are also presented and discussed.