Oxidation behavior of sputtered microcrystalline coating of superalloy K17F at high temperature

The influence of sputtering on the high temperature oxidation resistance of the cast superalloy M17F has been studied. The as-sputtered microcrystalline layer has a homogeneous γ phase structure with very fine grain size (20–100 nm), while the as-cast alloy is composed of γ, γ′ and carbides. The oxidation resistance of the microcrystalline coating of K17F alloy is much better than that of the as-cast alloy, and is even superior to that of the pack aluminized alloy. At the initial oxidation stage, the oxide scale which formed on the as-cast alloy is composed of complex oxides of Cr, Ti, Ni and Al. As the oxidation time is prolonged, the amount of α-Al2O3 increases and becomes the main product. However, the scale which formed on the microcrystalline coating consists only of α-Al2O3. Cyclic oxidation and acoustic emission examination showed that the oxide scale on the cast M17F alloy easily spalled during cooling, but the α-Al2O3 scale on the sputtered layer had excellent adhesion. The beneficial effects of microcrystalline structure on oxidation resistance are discussed briefly.