Ultra High Temperature Corrosion Behavior Of Al-Si Coating At Different Temperature And Its Modification Foundation

Gas turbine engine is an important symbol of national core competitiveness.Turbine inlet temperature is a major feature of advanced gas turbine engine.Thermal barrier coatings are internationally recognized as the most practical way to significantly improve engine service temperatures.The antioxidant corrosion capability of metal adhesive layer at extremely high service temperatures(ie,hot oxidation under salt conditions),especially its hot corrosion resistance,is directly related to the service life of the thermal barrier coating.This paper focuses on the research topic of "thermal barrier coating anti-ultra-high temperature oxidation corrosion metal bonding layer" and takes the Al-Si coating as the object,which has a good resistance to high temperature hot corrosion performance and can easily form the Al2O3 scale with good stability above 1000℃.On the basis of the research of the hot corrosion behaviors such as microstructures,hot corrosion kinetics and corrosion products after hot corrosion at 1050℃,1150℃ and 1250℃,this paper discusses the hot corrosion mechanism of Al-Si coating in ultra-high temperature environment.Meanwhile,this paper investigates the effect of pre-oxidation on the effect of improving the corrosion resistance of Al-Si coating on ultra-high temperature hot corrosion.Hence,it provides some theoretical basis and technical support for the development of new anti-ultra-high temperature oxidation corrosion metal bonding layer.The research work carried out and the results achieved are as follows:(1)The hot corrosion behavior of Al-Si coating in 75% Na2SO4 + 25% K2SO4 mixed sulphate under 1050℃ is investigated.The research has shown that the hot corrosion of Al-Si coating at 1050℃ is much more severe than that at the high temperature conditions.The hot corrosion of Al-Si coating begins to lose weight after 70 hours.At this moment,the surface of the loose oxide film has no longer a protective effect.Al and Ni in the coating directly interact with the molten salt.Moreover,Cr and Si in the coating is also directly involved in the reaction with the molten salt.Meanwhile,Ti in the superalloy matrix has also diffused to the surface.The corrosion layer has a depth of about 75 μm after 90 hours of hot corrosion.(2)The hot corrosion behavior of Al-Si coating in 75% Na2SO4 + 25% K2SO4 mixed sulphate under 1150℃ is investigated.The result shows that Al-Si coating has a catastrophic hot corrosion in mixed sulphate under 1150℃.The Si element is diffused outwardly during the hot corrosion process.70 hours later,the coating contains almost no Si element.After about 70 hours’ hot corrosion,the corrosion area around 50% of the coating has been completely peeled off.Furthermore,after 70 hours of hot corrosion,the diffusion zone in the residual region can effectively resist the erosion of the sulfate at this temperature,which will have a certain protective effect on the matrix.(3)The hot corrosion behavior of Al-Si coating in 75% Na2SO4 + 25% K2SO4 mixed sulphate under 1250℃ is investigated.The result shows that the corrosion products are completely peeled off when the hot corrosion reaches for 60 hours.The coating leaves only about 50% of the original coating.80 hours later,hot corrosion has lost weight to 15.85 mg/cm2 and the coating has been completely peeled off.In addition,the inner diffusion barrier can’t suppress the erosion of the molten salt for a long time in the environment which the sulfate is mixed at 1250℃.The cracks are appeared inside the diffusion barrier and they are rapidly peeled off.The matrix is destroyed by destruction.(4)Al-Si coating is the research object.We prefabricate a layer of protective oxide film about 8 microns thick on its surface and investigate its hot corrosion behavior in 75% Na2SO4 + 25% K2SO4 mixed sulphate under 1150℃.Moreover,we have systematically studied the growth and failure process of oxidation film under molten salt,the dynamic behavior of hot corrosion,products of hot corrosion at different times and so on.The research shows: the pre-oxidization Al-Si coating is heated at 1150℃ for 60 hours before hot corrosion in the sulfate,and its surface is formed with a continuous dense protective oxide film mainly composed of alumina.Moreover,the hot corrosion dynamics curve shows the approximate parabolic law.After 150 hours of hot corrosion,the internal diffusion barrier of aluminum-silicon coating composed of Cr,Si,Ni and other elements better inhibits the O,S and other elements continuing to invade.It can be said that the matrix is still the effective protection of the coating in the extreme environment for a long time.It indicates that the pre-oxidation treatment can better improve the service life of aluminum-silicon coating over 1000℃.In summary,the Al-Si coating suffers from more severe hot corrosion in mixed sulphate over 1000℃.And the pre-oxidation has a certain effect on improving its anti-high temperature hot corrosion performance.The results of this research further confirm that it is necessary to pay more attention to its ultrahigh temperature hot corrosion behavior and mechanism in the research process of anti-ultra-high temperature oxidation corrosion metal bonding layer.