Thermodynamical and experimental investigation on the oxidation behavior of aluminized Hastelloy C276 alloy

Abstract

Abstract In this study, the effect of aluminizing temperature and time on the oxidation behavior of Hastelloy C276 are investigated. Aluminide coatings are obtained at 600, 650, and 700 °C for 2, 4, and 6 h, and characterized by microstructural analysis, thermodynamic modelling, and thermogravimetric analysis at 900 °C. The coating formed on the surface has a diffusion-controlled growth characteristic, and as the process temperature and time increase, the coating thickness is also increased. The aluminide layer develops due to interdiffusion between aluminum and substrate elements, resulting in compositional gradients mainly consisting of nickel, chromium, and molybdenum. Thermodynamic modelling indicates that oxidation is governed by Al2O3 formation, while experimental results have shown that aluminizing significantly reduces oxidation kinetics. The alloy aluminized at 600 °C for 6 h exhibits the lowest weight gain and forms a continuous and compact oxide layer. In contrast, higher aluminizing temperatures result in non-uniform oxide morphologies and increased oxidation rates. Cross-sectional analyses have revealed that oxidation behavior is directly related to the stability of the aluminide layer and the development of the diffusion zone. The results indicate that preserving the Al reservoir by limiting excessive interdiffusion is critical for achieving a stable and protective oxide scale.