Research For Anti-oxidation Performance Of Al-Si Coating With Different Content

Based on areo engineer turbine, Al-Si coating were prepared on nickle-base superalloy K4104 by slurry process. Three Al-Si coating with different content were attained by changing adding of CrO₃ in slurry. They are Al-Si coating adding a little of CrO₃, Al-Si coating adding no CrO₃ and Al-Si coating adding a lot of CrO₃. Static oxidation resistance of three Al-Si coating were carried out under 1000℃ for 5hr 25hr 50hr 100hr 150hr 200hr respectly. Oxidation kinetics equation of three Al-Si coating are X⁴.40=106.65t X⁴.26=282.03t X³.375=60.02t, they are not simple parabolic equations,which exponent (n) is higher than 2.This mean that oxide scale formed on Al-Si coating is compact. Oxidation kinetics were drawed by origin. According to oxidation kinetics, oxidation rate of early oxidation stage is fast. With α -Al2O3 forming,oxidation kinetics become flat.Oxidation kinetics of Al-Si coating with adding a little of CrO3 is lower than Al-Si coating with adding no CrO3 and Al-Si coating with adding a lot of CrO3, which result from that its oxide scales is more complat. Oxide scales and cross section were studied by SEM with EDX. It found that forming 8 -Al2O3 is dominate in the early stage. With prolong of oxidation time, 9 -Al2O3 transform to α -Al2O3, then a -Al2O3 forming is dominate. A little of Cr²+ stimulate transformation from θ -Al2O3 to α -Al2O3, so the transformation of Al-Si coating with adding a little of CrO3 finished quickly. There are many Cr2O3 TiO2 NiAl2O4 formed on the Al-Si coating with adding no CrO3 and Al-Si coating with adding a lot of CrO3, which destroy the compation and continuance of oxide scales. Cr2O3 TiO2 NiAl2O4 may peel off which result in Al diffuse outward form new oxide scales. From cross section, oxide scales outside layer middle layer and diffusion layer can be seen.There are continuous oxide scales on the Al-Si coating. Outside layer are made of β -NiAl during 200hr. Al-Si coating with adding a little of CrO3 form "obstacle"rich in Si which hinder interdiffusion of Al and elements of alloy. Therefor Al-Si coating with adding a little of CrO3 has better oxidation resistance.