Research On Microstructure And High-temperature Oxidation Property Of Al-Si Coatings On 1Cr11MoNiW1VNbN Stainless Steel

In this paper, Al-Si coating was prepared on 1Cr11MoNiW1VNbN stainless steel by slurry process to improve application temperature of ultra steam turbine blades. According to the criterion of GB/T13303-91 and HB5258-2000, the isothermal oxidation testing at 700℃in air for 1000h and oxidized circularly at 700℃for 11 times was carried out.The composition, structure, surface morphology and the failure causes of Al-Si coating were analysised and researched by the analysis and detection methods of SEM, EDS, XRD and so on.The Al-Si coating prepared by slurry process includes outer layer, intermetallic compound layer and transition layer.The Al-rich outer layer mainly contains the phase ofα-Al and few FeAl3, whose thickness is about 8μm. The metal compound layer is about 16μm. and the main component is the Fe2Al5 phase.The transition layer is about 14μm and its composition approach to the matrix organizations.The Metallic compound layer is the effective protection against high temperature oxidation,which is dense, uniform, smooth and consolidated well.The results indicated that, the dense and continuous oxide films ofα-Al2O3 with a certain thickness formed on the surface of Al-Si coating at 700℃for 1000h were the barriers in the high temperature oxidation.The oxides of FeAl2O4 and FeO generated in the early oxidation produce compressive stress,while the transition fromθ-Al2O3 toα-Al2O3 produces tensile stress in oxide film.Those stresses and the holes in the coating will cause oxide film cracked and spalled.But the enough Al element provided by phase transition from FeAl3 and Fe2Al5 to FeAl can keep the repaired formation of the oxide film itself. Si elements in the coating can effectively control the growth of brittle phase, improve the plastic of Al2O3, promote phase transition fromβtoγ', reduce the brittle-plastic transition temperature and increase the adsorption capacity of coating;The second phase particles formed by Si and alloying elements can effectively hind interdiffusion of the coating and substrate alloying elements, and the performance of high temperature oxidation resistance of the coating is improved.Assessing by the standards of GB/T13303-91 and HB5258-2000, Al-Si coating is completely antioxidant, and the oxidation rate was significantly lower than uncoated samples.The Al-Si coating has a better ability than uncoated samples in the high temperature oxidation and cyclic oxidation.