Oxidation behaviour of nanocrystalline Fe–Ni–Cr–Al alloy coatings

Nanocrystalline Fe–Ni–Cr–Al alloy coatings with ∼4 wt-%Al were produced using the unbalanced magnetron sputter deposition technique with a composite 310S stainless steel target embedded with aluminium plugs. The oxidation behaviour of the coatings was studied, during which complete external α-Al2O3 scales were formed. During isothermal oxidation tests at 950, 1000, and 1050°C, the oxidation kinetics followed an essentially parabolic rate law, and the oxidation constants were measured to be 2·06 × 10-3, 4·23 × 10-3, and 1·14 × 10-2 mg2 cm-4 h-1 respectively. During a cyclic oxidation test at 1000°C the α-Al2O3 scale showed good scale spallation resistance. The surface hardness of the coatings was measured with a Knoop indentor before and after oxidation. After oxidation, the coating surface hardness was still significantly higher than that of the uncoated specimen, demonstrating the potential this coating has in the improvement of high temperature erosion resistance.