Role of nano-HfC addition in enhancing oxidation resistance and modifying scale evolution in Inconel 625

Abstract

Inconel 625 alloys are widely utilized in high-temperature applications due to their excellent mechanical properties and corrosion resistance; however, their oxidation resistance remains insufficient for more demanding environments. This study addresses this limitation by incorporating nano-sized hafnium carbide (nano-HfC) particles into Inconel 625 (IN625) coatings to enhance their high-temperature oxidation performance. The coatings were fabricated and subjected to isothermal oxidation tests at 900 °C, 1000 °C, and 1100 °C. Performance evaluation reveals that the IN625/HfC coatings exhibit markedly lower oxidation mass gains compared to IN625, with reductions of 33–40 %, along with a decrease in the parabolic rate constant (k_p) of approximately 56–65 %, indicating a significant improvement in oxidation resistance. Introducing nano-HfC significantly refines the grain structure, promotes chromium diffusion, and facilitates the in-situ formation of HfO₂ nanoparticles, which serve as effective nucleation sites for Cr₂O₃ and diffusion barriers against oxygen ingress. Mechanistic analysis reveals that incorporating nano-HfC alters the dominant oxidation mechanism from outward cation diffusion to inward oxygen diffusion, thereby transforming the residual stress state from tensile to compressive. This modification enhances oxide scale adhesion and suppresses spallation. This work provides new insights into microstructural engineering strategies for significantly improving the oxidation resistance and long-term service stability of Inconel 625.