Oxidation Resistance Of K4104 Superalloy With A1 Protective Coating At High Temperature

Superalloy is the key materials for aero-engine. The development of superalloy is the foundation of the advance of aero-engine to some extent. Superalloy exhibits higher oxidation/hot corrosion rate at high temperature, therefore, protective coating is hot topic in the surface engineering field. Higher temperature coating can be dividing into diffusion coating and overlay coating. Aluminize diffusion coating is widely applied in the corrosion field.In this thesis, the Al-Si and Al coating on the surface of K4104 superalloy were prepared using slurry method from the Al and Al-Si powders, respectively. For comparison, NiY and Y2O3 modified aluminide coatings deposited on K4104 superalloy were also prepared in order to investigate the reactive element effect. The microstructures and the oxidation performance of various aluminide coatings were investigated using scanning electron microscopy with an energy-dispersive X-ray analysis (SEM/EDX), X-ray diffraction (XRD), and thermal-gravimetric analysis (TGA). The anti-oxidation mechanism of aluminized coatings was discussed.Aluminizing increased the oxidation resistance of K4104 superalloy. During the initial oxidation stage, the oxidation scale consisted ofθ-Al2O3. With the increasing of oxidation time, the main composition of oxidation scale wasa-Al2O3, which led to the cracking of oxidation scale. The content of aluminum obviously decreased due to inner and outer oxidation. When the aluminum content of coating was less than 15%, the oxidation resistance of aluminiuming coating significantly deteriorated.The oxidation resistance of Al-Si coating was superior to that of aluminized coatings. After the addition of Si, CrxSiy was formed and scattered in the Al-Si coating, which hindered the formation ofα-Cr phase. Meanwhile, the addition of Si led to the formation of chromate-enrichment solution and carbide on the coating/substrate interior. Moreover, Si accelerated the conversion ofθ-Al2O3 toα-Al2O3 and increased the oxidation resistance of Al-Si coating.After the addition of Y2O3, bulk CrxSiy was formed on the coating suface, while, CrxSiy was formed and scattered in the Al-Si coating with the addition of NiY. Both Y2O3 and NiY had accelerated effect on the phased transition ofθ-Al2O3 toα-Al2O3. Comparing with Y2O3, NiY decreased the oxidation rate and defect formation rate at the interior of oxidation scale and coating, which indicated the anti-oxidation performance of coating was improved.By the comparison of oxidation resistance of different coatings, the oxidation resistance of four coatings can be ranked as an increasing series:aluminized coating< Al-Si coating< Al-Si-Y2O3 coating< Al-Si-NiY coating.