Preparation Of Multi-arc Ion Plating NiSiAlY Coating And Research On Hot Salt Corrosion Performance

Due to the high service temperature of the last two stage blades of high-pressure compressor in aero-engine,nickel base superalloy is usually used as the blade material.The hot corrosion of nickel base superalloy is very easy to occur under the NaCl deposit in the marine environment.At present,the main component of the common protective coating for aircraft engine blades is M（M=Ni,CO）CrAlY.However,in the high NaCl environment,the Cr-rich coating will be corroded severely,thus it cannot protect the inner substrate.Therefore,in order to protect the aero-engine from hot corrosion caused by high salt environment,and keep the workpiece service in a good working condition,it is urgent to develop a coating without Cr.NiSiAlY coating is a kind of feasible alternate.In this paper,the NiSiAlY coatings were prepared,and the hot corrosion mechanisms of the coatings were studied.1)NiSiAlY coatings with different Si contents（2.5 wt.%,4.5 wt.%,6.5 wt.%,8.5wt.%,10.5 wt.%）were prepared by Multi-arc Ion Plating.The surface morphology and cross-section structure of the coating do not change with the increase of Si content.The main phases in the coating areγ-Ni/γ’-Ni₃Al andβ-NiAl.β-NiAl is the main phase to form a layer of protective scale.2)It was found that the coating with 2.5 wt.%Si content had the best hot salt corrosion resistance at high temperatures.A layer of dense oxide scale was formed on the surface of the coating during corrosion,and element diffusion was not so severe between the substrates and coatings.With the increase of temperature,corrosion became more and more severe.3)NiSiAlY/Al coating was prepared by Multi-arc ion plating,and a dense oxide scale was successfully formed on the surface of the coating by pre-oxidation.The main phases of the coating were stillγ-Ni/γ-Ni₃Al andβ-NiAl.After pre-oxidation,the oxides of Y were formed at the interface between oxide scale and coating.4)The hot salt corrosion resistance of the coating samples with pre-oxidation and without pre-oxidation were performed at 750℃.Due to the salt particles promoting the corrosion of the coating,a lot of Kirkendall effect voids were formed in the coating without pre-oxidation during corrosion,and then internal oxidation occurred along the inner wall of the voids.However,for the coating with pre-oxidation,due to the oxide scale on the surface,the direct contact between the coating and the salt is prevented,and the internal corrosion of the coating is not very serious.After a long time of corrosion,the surface of the coating peeled off due to the cracking of oxide scale.5)A large amount ofθ-Al₂O₃ was produced in the coating without pre-oxidation during corrosion.As the corrosion proceeded,θ-Al₂O₃ gradually transformed toα-Al₂O₃;However,after pre-oxidation,the coating does not produce a large amount ofθ-Al₂O₃,and the thickness of oxide scale also grew uniformly with the corrosion time.It can be inferred that NaCl will catalyze the coating to formα-Al₂O₃.