| The turbine blades in aerospace are typically protected by a protective coating to improve the corrosion-resistant property. Diffusion-aluminide coating is above 80% percent in hight temperature coating. Because diffusion-aluminide coating not only satisfieds ordinary property1 demands but also has low cost and steady performance. At this paper, the aluminized coating on K438 was prepared by pack cementation. The isothermal oxidation behavior of the coating was investigated at 1000癈 in air for 500 hours. The oxidation kinetics curve was drawed. The surface morphology and cross-sectional microstructure of the coating oxidized for different time were observed and analyzed by SEM, OM and EDX. The degradation mechanism of the coating is discussed. The resistance of high temperature oxidation on an aluminide-coated nickel-base superalloy K438 is appraised.The results show that oxidation kinetics curve about an aluminide-coated nickel-base superalloy K438 obeys the parabolic law. The mass gain of the aluminized coating is lower than raw material , the oxidation resistance is remarkably improved as compared to the superalloy K438. The material has well oxidation resistance mostly because of the forming of a -Al2O3 oxide scale, a ?Al2O3 oxide scale is very compact, it has steady chemical property and excellent resistance of oxidation and hot corrosion. The adhesion between the oxide scale and substrate is good. After 100 hours oxidation, some slight spallation is observed on the surface. The oxide scale becomes compact and full again in 200, 300 and 400 hours. In 500 hours, there are part spallations. By analyzing the EDX, it is still a - Al2O3 scale. Through the high temperature oxidation, the coating has changed to Ni-rich and Al-rich 3 -NiAl compound layer, this compound layer is significant in the oxidation resistance. -NiAl layer is thick, As the oxidation time extending, -phase degrades slowly. The oxidation resistance of the coating in 500h is still well.
|
PDF Full Text Request