Research For High Temperature Oxidation Properties Of Al-Si Coating On K438 Superalloy

The turbine blades in aerospace are typically protected by a protective coating to improve the oxidation-resistant property of the substrate. Aluminized silicon coating has well oxidation-resistance which is related to the reasonable profile of silicon. The Aluminized silicon coating on superalloy K438 is prepared by diffusing in high temperature. The oxidation behavior of the coating is investigated at 1000 in air, for 500h by OM, SEM, EDX, and so on and the role of the silicon is also investigated. The kinetic analysis o f the coating is done by the oxidation kinetics. The Aluminized silicon coating has better oxidation resistance than the Aluminized coating which can be observed through kinetics.Morphology of the Aluminized silicon coating is investigated through XL-300FEG SEM. A12O3 is formed at the surface of the coating. The peeling of 'the coating at long time oxidation is obvious. But the new film of Al2O3 will form to protect the substrate.The morphology o f cross section is investigated by SEM and the thickness o f the film is also measured. The element profile in the coating and substrate can be researched by EDX. The Aluminized silicon coating has changed to Ni-rich and Al-rich P -NiAl which can improve the oxidation-resistance of the coating.The distribution o f silicon in Aluminized silicon coating mainly in the internal coating where the concentration o f silicon is high and in the Si-rich MeC and [Niie (TiCre) Si7] barrier. The silicon can delay the degradation of phase. The silicon can also promote the transformation from 3 -phase to Y ' -phase. The si-rich Y ' -phase has better oxidation resistance which can be compared with -phase. The transformation from the 3 -phase to Y ' -phase can decrease the DBTT. The Si-rich barrier impedes Al and O diffusion into matrix of alloy, therefore rises oxidation resistance of Aluminized silicon coating at high temperature.