Study On Microstructure And Properties Of New Co Based Superalloy Coatings By Plasma Cladding

Co-based superalloys have excellent wear resistance,corrosion resistance and high temperature oxidation resistance at operating temperatures above 730℃,and which can be used as surface protective coatings for high temperature vulnerable parts.In this paper,Co-based superalloy coatings with different contents of Y₂O₃ and Al were prepared by plasma cladding technology,and the microhardness,corrosion resistance and oxidation resistance of the coatings were studied by Vickers microhardness tester,electrochemical workstation,and oxidation experiments,respectively.X-ray diffractometer（XRD）,scanning electron microscope（SEM）and energy dispersive spectrometer（EDS）were used to study the microstructure of the coatings and their oxided layers,and to explore the oxidation mechanism of the coatings.The results show:（1）Compared with the Co-based coating without added elements,the microstructure of the coating with 0.5wt.%Y₂O₃ is refined,and the Al-enriched area appears in the coating with Al added individually.There are no Al-enriched areas in the coating of the mixed addition of 0.5wt.%Y₂O₃+5wt.%Al,thus it can be deduced that the microstructure of the coating is improved due to the purification effect of Y₂O₃.（2）The surface hardness of all the coatings after adding Y₂O₃ and Al is improved to different degrees comparing with the hardness of the none addition of Co-based superalloy coating,and the hardness of the coating with 0.5wt.%Y₂O₃+5wt.%Al is the most improved.The results of electrochemical experiments show that the coating with0.5wt.%Y₂O₃+5wt.%Al has the best corrosion resistance,followed by the coating with5wt.%Al and 0.5wt.%Y₂O₃respectively.（3）Cyclic oxidation experiments show that the oxidation resistance of the coating mixed with 0.5wt.%Y₂O₃+5wt.%Al are the best at both 900℃and 1000℃.The surface oxide films of all sample coatings are mainly composed of Cr₂O₃ and spinel oxides,while Sican form SiO₂ oxide films in Cr-poor regions.Al₂O₃ oxide film appeared in the coating with Al addition,especially in the coating with 5wt.%Al addition,and a double-layer oxide film of Cr₂O₃ and Al₂O₃ was formed,which could further improve the oxidation resistance of the coating.In addition,in the mixed addition of 0.5wt.%Y₂O₃+5wt.%Al coating,the formed Al₂O₃ oxide film and the effect of Y₂O₃ improved the oxidation resistance of the coatings.（4）Comparing the oxidation at 900℃ and 1000℃,the oxidation rate of all coatings at 1000℃ is faster than that at 900℃ due to the increase in temperature.However,compared with other coatings,at 1000℃,the oxidation rate of the coating mixed with 0.5wt.%Y₂O₃+5wt.%Al has a smaller increase than that at 900℃,indicating that the coating mixed with 0.5wt.%Y₂O₃+5wt.%Al is relatively stable and has excellent oxidation resistance.