Corrosion degradation and interface behaviour of magnetron sputtered NiAl coatings doped with Zr, Hf, and Cr

In this work, NiAl-based coatings doped with optimised Zr, Hf, and Cr content are deposited via magnetron sputtering and evaluated for hot corrosion performance. Systematic high-temperature corrosion tests and microstructural analyses reveals that the corrosion resistance and oxide scale adherence of the coatings are strongly dependent on the dopant type and content. Among the single-element doped coatings, NiAlZr exhibits the highest corrosion resistance but suffers from poor scale adhesion, whereas NiAlCr shows the lowest corrosion resistance yet excellent adhesion due to the formation of porous internal and external oxide layers. NiAlHf coating demonstrates intermediate performance. Mechanistically, Zr/ZrO₂ particles effectively suppress the β→γ/γ′ phase transformation and stabilise the grain structure, while HfO₂ promotes interfacial transitions that improves scale anchoring. The presence of Cr will reduce the lattice mismatch but potentially disrupted γ′ ordering. Furthermore, surface wettability and roughness are observed to govern salt mist deposition behaviour, with smoother, more hydrophobic coatings (NiAlZr and NiAlHf) resisting salt accumulation. Notably, a significant synergistic effect between Zr and Hf identified in co-doped NiAlZrHf coating, which outperforms the single-doped counterparts. These findings offer insights into compositional tailoring strategies for enhancing hot corrosion resistance in advanced aluminide coatings.