Research On High Temperature Properties Of Aluminide Coating By CVD Methods

An aluminide protective coating is required on the inner cavity and surface of aero-engine hollow blades.Chemical vapor deposition(CVD)can be used to prepare aluminide coatings on the inner cavity and surface of the blade,the working environment of the hollow blade is complex.It is often affected by thermal shock and high temperature corrosion.Aluminide coating can play a protective role to a certain extent,especially the aluminide coating with modified elements.Aluminide coating can improve the service life of the hollow blade of air engine.However,the preparation process of aluminide coating is carried out at high temperature,which may adversely affect the mechanical properties of hollow blades.Two aluminide coatings,namely single aluminide coating and yttrium modified aluminide coating,were prepared by CVD method.The coating is composed of obvious diffusion layer and outer layer,and the coating structure is uniform.The addition of Y in the coating improves the Al content in the outer layer of the coating.The surface phase of the coating group Chengdu is a single beta-NiAl phase.In this paper,100 h high temperature corrosion test was carried out at 900 C.The results show that the high temperature corrosion resistance yttrium modified aluminide coating is better than single aluminide coating,single aluminide coating is better than GH4169 substrate.There are localized corrosion pits on the surface of the single aluminide coated sample,the boundary of the cross section coating is blurred,there is a clear crack between the coating and the substrate,sulfur is found in the matrix,local corrosion failure occurred in the coating.The surface of yttrium modified aluminide coating has no obvious corrosion and spalling,the cross section coating is clearly defined,there is still a high Al content in the outer layer of the coating,and the surface still contains the beta-NiAl phase.Y can improve the binding force of the oxide film,improve the plasticity of the oxide film,prevent the interdiffusion between the coating and the matrix elements,promote the change of the growth mechanism of the oxide film to the internal diffusion of oxygen,and then improve the high temperature corrosion resistance of aluminide coating.In this paper,the thermal shock tests under 900 cooling conditions,namely,water cooling and air cooling at two degrees,are carried out.The results show that after 520 heat shocks,the surface crack of single aluminide coated sample is longer and denser than that of yttrium modified aluminide coating.The Y element can increase the binding force between the oxide film and the coating,and easily gather at the defect.It plays the role of "pinning",which inhibits the crack growth and crack initiation.Heat shock under air cooling condition,after the 1000 thermal shock,the two samples showed no cracks and spalling.The two kinds of coatings show good thermal shock resistance.The effect of CVD process on the high temperature endurance and low cycle fatigue properties of GH4169 nickel base superalloy substrate has been studied.The results show that after the aluminizing treatment,the GH4169 material has a increase of 1.0% at 650 high temperature and a decrease of ℃ 4.7% at 455℃.