Understanding Ni2AlHf-accelerated high-temperature corrosion in Hf-doped NiAl alloys: Insights from DFT calculations

The extremely prominent enhancement of high-temperature oxidation resistance in NiAl-based alloys/coatings by Hf addition is attributed to the reactive element effect. Few studies have focused on hot-corrosion resistance of Hf-doped NiAl alloys, and the sensitivity to Hf content needs further research. In this study, we prepare five types of NiAl alloy samples (0, 0.1, 0.3, 0.5, 1.0 at% Hf), with a NiAl-Ni₂AlHf dual-phase structure. First-principles calculations and experimental observations reveal that the Ni₂AlHf content directly affects the service performance of the NiAl alloy. Compared to the NiAl phase, Ni₂AlHf exhibits greater ability to adsorb environmental media (O, S, and Cl). It also exhibits surface stress differences with NiAl, both of which lead to poor oxide adhesion and nucleation of HfO₂ particles during short-term hot corrosion. The thermodynamic formation energy and kinetic diffusion barriers of O and S at the NiAl/Ni₂AlHf interface determine their interfacial segregation tendency. The interfacial accumulation behavior of O and S leads to severe internal oxidation and sulfidation, inhibiting the formation of protective oxide scales. Introducing 0.1 at% Hf is determined to be the most optimal for achieving balanced enhancement of the oxidation and corrosion resistance of the NiAl phase, providing a foundation for the design of NiAl-based alloys/coatings.