Low Temperature Plasma Spraying MCrAlY Coating And Its High Temperature Corrosion Performance

A major factor stop the gas turbine long-serving is the corrosion of blade. Usually, high-temperature protective coating is needed to protect the blade. Recent research at home and abroad focuses on prepareing good protective high-temperature protective coatings which has strategic importance to national defense security and national economy.In this paper, NiCrAlY coating and NiCoCrAlYTa coating were prepared on Ni-based superalloy K417 and K438 substrates. High-temperature oxidation experiment was conducted. The key is high-temperature molten salt corrosion experiment. High-temperature oxidation and molten salt corrosion performance are studied.Microstructure, evolution, element distribution, kinetic rule and phase of coatings and substrates at different times were tested by SEM, EDS and XRD. The results are as follows.(1)NiCrAlY coating and NiCoCrAlYTa coating prepared by low pressure plasma spray method are uniform dense. After heat-treated 4h at 1080℃ in vaccum furnace, the interface between coating and substrate became dim. Metallurgical bonding occurred between coating and substrate.(2)NiCrAlY coating and NiCrAlY powder have the similar phases. But γ’-Ni3Al increases greatly. γ’-Ni3Al shows good mechanical strength under the condition of high temperature.(3)The oxidation kinetic curves of NiCrAlY coating at 950℃ obey parabolic law. A 1.5um thick Al2O3 layer formed on the surface of coating after 100h. Mass gain of K438 substrate is very fast at the beginning of oxidation.The mass gain reaches 2.395mg/cm2. Then, violent mass loss happens.(4)The corrosion resistance performance of K417 substrate is zero under the condition of 950℃ molten salt corrosion. Violent mass gain happens. Compared to K417 substrate, K438 substrate is much better on corrosion resistance performance. Mixed corrosion products including Al2O3 and NiO form on the surface.(5)A uniform dense Al2O3 layer forms on the surface of NiCrAlY coatings prepared on two kinds of substrates after molten salt corrosion 500h at 950℃. The corrosion kinetic curves obey parabolic law. Convex hull and missing happen for NiCoCrAlYTa coatings prepared on two kinds of substrates after molten salt corrosion 500h at 950℃. Flaky Al2O3 still exists on the surface of NiCoCrAlYTa coating prepared on K438 substrate. Two kinds of NiCoCrAlYTa coatings don’t obey parabolic law.The work of dissertation is supported by National 863 High-Tech Program (2012AA03A512) and 973 Project (2012CB625100).