Study On High Temperature Oxidation Resistance Of Pt-Modified Aluminide Coatings On K438 Superalloy

In order to improve the high-temperature oxidation resistance of nickel-based superalloy K438,a protective aluminide coating can be applied on its surface.Hot-dip aluminum plating is an efficient method for implementing aluminide coating,which has the advantages of high production efficiency,low cost,simple operation and long effective protection period.However,a single hot-dip aluminum coating often has defects such as a faster degradation rate.In order to slow down the degradation rate of the coating,the modification element Pt can be added to extend the service life of the coating.Therefore,in this study,the magnetron sputtering（PVD）method was used.First,a layer of Pt with a thickness of about 2μm was deposited on the K438 alloy.After 1050°C and 2 hours of vacuum diffusion treatment,the hot-dip aluminizing experiment was performed.This experiment is based on GB/T13303-9"Determination of oxidation resistance of steel"and HB5258-2000"Determination of oxidation resistance of steel and high temperature alloys".Cyclic oxidation tests of naked K438,traditional hot-dip aluminum coating and Pt modified hot-dip aluminum coating were carried out at 1000℃and 250 times.Its oxidation behavious including oxidation kinetics of the sample after high temperature oxidation,the surface oxidation product morphology and phase composition,and the cross-sectional morphology were studied by TGA,SEM,XRD and EDS.The results show that after 250 cycles of oxidation at 1000°C,the substrate K438alloy has poor high-temperature oxidation resistance,and a Cr₂O₃ film is formed on the surface.The cross-sectional analysis found that the K438 alloy has undergone severe internal oxidation,and the internal oxide Al₂O₃ is distributed at the oxide film/matrix interface.The high-temperature oxidation resistance of a single hot-dip aluminum coating is better than that of the base K438 alloy,and the high-temperature oxidation resistance of the coating with a dipping time of 90s is the best.The surface of a single hot-dip aluminum coating produces an Al₂O₃ film with better protective properties.The cross-sectional analysis found that theα-Cr particles precipitated by the 30s and120s coatings of hot-dip aluminum plating with poor high temperature oxidation resistance are coarse and unevenly distributed,while theα-Cr particles precipitated by the hot-dip aluminum coatings 60s,90s and 180s The particle size is small and uniformly distributed.The Pt modified hot-dip aluminized coating has better high-temperature oxidation resistance than a single hot-dip aluminized coating.The coating with a dipping time of 90s has the best high-temperature oxidation resistance.The Al₂O₃film formed on the surface of the Pt modified hot-dip aluminum coating is more dense.Cross-sectional analysis found that theα-Cr particles precipitated after the oxidation of the Pt modified hot-dip aluminum coating for 60s,90s,120s,and 180s are all small in size and uniformly distributed.