Oxidation Behavior of Sputter Deposited Nanocrystalline and Conventional Plasma Sprayed MCrAl(Y) Coatings

Abstract

The MCrAl-type coatings with, or without, yttrium are widely used for oxidation and/or hot corrosion protection of hot section components of gas turbine engines. Recently, there has been great interest in developing nano or microcrystalline coatings since these coatings offer excellent oxidation and corrosion resistance compared to the conventional coatings. Cyclic oxidation and microstructral degradadation behavior of sputter deposited nanocrystalline Ni-20Cr-10Al coating has been investigated at 1010°C. The coating was deposited on Haynes 230 samples using a magnetron sputtering technique. This technique produced a coating with a grain size of ∼9 nm. The cyclic oxidation results showed that the sputter deposited Ni-20Cr-10Al coating exhibited better oxidation resistance in terms of weight loss kinetics compared to the conventional plasma-sprayed NiCoCrAlY and PWA 286 coatings. The Al content in the nanocrystalline coating was consumed in a relatively short time due to inward and outward diffusion of Al. The accelerated consumption of Al was presumably due to enhanced grain boundary diffusion resulting from the ultra-fine grain structure in the coating. Variation of oxide-scale spallation resistance during thermal cycling, internal oxidation of the coatings, and the rate of Al consumption due to inward and outward diffusion of Al between the nanocrystalline and plasma sprayed coatings is presented.