Researching On High-temperature Oxidation Property Of NiCrAlY Coatings On Nickel-base Superalloy K465

The continued development of the aero-engine industry puts forward the hot endcomponents such as the blades with a higher operation temperature. In order to improve theoperation temperature of the blades and prolong its service life, the NiCrAlY coatings weredeposited on the superalloy K465by arc ion plating. According to the standard ofGB/T13303-91and HB5258-2000,and the actual operation conditions and temperature of theblades, the isothermal oxidation testing of the NiCrAlY coatings and alloy samples at1100℃in air for200hours was carried out. The oxidation kinetics law, oxidation thermodynamics,oxidation resistance,the surface and cross-section morphology of the oxides, the phasecomposition,the rules of elemental diffusion and the degradation mechanism of the coatingwere discussed by the analysis and detection methods of SEM, EDS, XRD and so on.The NiCrAlY coating after vacuum diffusion were deposited continuously and denselyon the surface of alloy K465. There was a diffusion layer between the coating and thesubstrate alloy. The diffusion layer connected the coating and the substrate alloy by themetallurgical bonding. The coating and diffusion layer consisted of β-NiAl and γ ’-Ni3Al.The results showed that:The oxidation kinetic of alloy K465with coating followed parabollic rate law under1100℃for200h. The alloy K465with NiCrAlY coating retained excellent oxidation resistantperformance. The uninterrupted α-Al₂O₃and θ-Al₂O₃membrane was formed in the earlyand θ-Al₂O₃into α-Al₂O₃at later stage. The oxide film was Complete and dense becauseof better performance of α-Al₂O₃. Because Al was consumed, there was β-NiAlâ†'γ ’-Ni₃Alâ†'γ-Ni in the coating and diffusion layer. Although the coating was a certain degree ofdegradation, but the coating still has a very effective antioxidant.In the initial stage of high temperature oxidation, the K465sample’s surface was coveredby protective oxide film of Al₂O₃and Cr₂O₃to protect he samples. TiO2and NiCr₂O₄increased in the medium-term of oxidation and undermine the integrity of the oxide film dueto their different physical properties such as thermal expansion coefficient of Al₂O₃and Cr₂O₃.It reduced the adhesion of the oxide film and dense and lead to a large number of oxide filminitiation of cracks and spalling of the oxide film. The surface of samples was covered againby protective oxide film. The newly formed oxide film does not have good adhesion, and spill again. The loss of beneficial elements in the alloy specimens formed many defects in the alloysurface for the O^2-to spread. The oxide film of sample with varying degrees of internaloxidation was loose even empty. So the alloy K465do not have the ability to wok long time athigh temperatures.