Micropores governed high-temperature oxidation behavior of Cr coatings: Kinetics analysis and phase-field modeling

Micropores are often regarded as external issues and receive less attention in material oxidation research. Here, the high-temperature oxidation performance of ∼15 μm Cr coatings on Zr alloys in 1000–1200 °C steam is studied, revealing that the oxidation behavior is governed by the pore-generation process associated with the intrinsic properties of coatings. During oxidation, three distinct kinetic stages are observed: an early parabolic stage, a parabolic-deviation stage, and a subsequent acceleration stage. The small characteristic sizes of the coatings suppress dislocation activity, leading to the accumulation of oxidation stresses at the Cr₂O₃/Cr interfaces. This process induces pore aggregation in Cr₂O₃ and the corresponding kinetic transition from stage I to II. Subsequently, the outward diffusion of Zr results in the formation of pores at both the Cr/Zr interfaces and within the coatings, triggering the coating structural collapse and driving the kinetics transition from stage II to III. Phase-field simulation is conducted to elucidate the pore-generation mechanism and its impact on the oxidation behavior of Cr coatings; a universal oxidation kinetics map is also constructed. This study provides a unique insight into the high-temperature oxidation mechanism of coating materials.