Study On High Temperature Oxidation Resistance Of Laser Cladding NiCrAlTa Coating On GH625 Nickel Base Superalloy

In order to improve the high temperature oxidation resistance of GH625 nickel base superalloy at high temperature,NiCrAlTa coatings with different Ta contents and NiCrAlcoatings were prepared on its surface by laser cladding technology.The isothermal oxidation tests were carried out at 950℃and 1050℃for 200h to study its oxidation behavior at high temperature.The results show that:（1）At the two test temperatures,the oxidation weight gain per unit area of the coating decreases with the increase of Ta content.The fitted curves conform to the parabolic law,and the parabolic rate constant decreases with the increase of Ta content.This is because the increase of Ta content improves the adhesion between the oxide film and the coating,thus reducing the oxidation rate.（2）The oxide formed on the surface of NiCrAlcoating mainly includes Cr₂O₃.Ni Cr₂O₄ and a small amount of Ni O,NiCrAlTa coating surface oxides mainly include Cr₂O₃.Ni Cr₂O₄ and Cr Ta O₄.iith the increase of Ta content,the Cr Ta O₄ content increase.Green oxide film was formed on the surface of the coating,and the oxide particles fell off seriously.iith the increase of oxidation time,the color of the oxide film became darker,and the amount of fallen oxide increased.（3）After isothermal oxidation at 950℃for 200h,a single Cr₂O₃ was formed on the surface of NiCrAland NiCrAlTa coatings.Internal oxidation zone appears under the coating,and the internal oxide is mainly Al₂O₃.iith the increase of Ta content,the thickness of the oxide layer on the surface of the coating decreases,and the cross section of the oxide layer is more uniform and dense,which is well combined with the coating.Single Cr₂O₃ film layer was formed on the surface of Ni Cr Al3Ta coating after oxidation at 1050℃for 200h,the internal oxide is mainly Al₂O₃,and part of the internal oxide forms an internal oxide layer.The oxide formed after 200h oxidation of Ni Cr Al9Ta is composed of outer layer Cr₂O₃.Ni Al₂O₄ and inner layer Al₂O₃.