Improvement of the oxidation behaviour of electron beam remelted MCrAlY coatings

The efficiency of gas turbine engines can be significantly improved by increasing their operating temperatures. The engine components, especially the hot-end components, should maintain their mechanical integrity at high-temperatures. The complex environment (thermal, chemical and mechanical) of the gas turbine engine makes it extremely difficult for one material to meet all the different requirements imposed on the various engine components.Coatings are thus required to provide increased corrosion protection at high temperatures in order to assure durability and field performance of the base alloys. Problems include: substrate compatibility, interdiffusion, adhesion, porosity of the coating, possibilities of repairing or recoating, effect of thermal cycling, wear and corrosion resistance and costs.Ni-base turbine blades are generally corrosion protected by an MCrAlY overlay and a ceramic thermal barrier top-layer, both thermally sprayed. A new technique used for these coatings is high-velocity oxygen-fuel (HVOF) spraying.A subsequent remelting of the HVOF-coatings by electron beam (EB) irradiation has proven to minimize the oxide content and the porosity of the thermally sprayed MCrAlY coatings. The surface was remelted up to a depth of approximately 30 μm. The high cooling rates produce modifications in the morphology and the phase composition of the MCrAlY coating.In this paper the influences of EB-remelting process on the characteristics of the thermally grown oxide (TGO) scale formed during oxidation in air at 950 °C in the MCrAlY coating will be discussed.