Abstract
Abstract The effect of nickel aluminide (NiAl) microcrystalline coating prepared by magnetron-sputtering on the high-temperature oxidation behavior of the NiAl-33.5Cr-0.5Zr (at%) alloy was investigated in static air from 1,000°C to 1,150°C. The additions of Cr and Zr changed the single β phase structure into the multiphase structure (β-NiAl, α-Cr, and Heusler [Ni2AlZr] phase). The NiAl-33.5Cr-0.5Zr alloy formed a nonprotective Al2O3 + Cr2O3 + ZrO2 (aluminum oxide + chromium oxide + zirconium dioxide) mixed scale and exhibited relatively large weight gains. The large weight gains were attributed to extensive internal oxidation. The sputtered NiAl microcrystalline coating remarkably improved the oxidation resistance compared to the NiAl-33.5Cr-0.5Zr alloy due to the formation of a continuous Al2O3 scale from 1,000°C to 1,150°C. The metastable θ-Al2O3 → α-Al2O3 transformation was identified by x-ray diffraction (XRD) results and a change in the morphology of scales also occurred with the transformation.
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