GUO Yunshan,WANG Jing,LI Yanyan,BAO Zebin,YUAN Kang,LIU Jianming.Influence of Sand Blasting on Microstructure at Interface of MCrAlY Coating and Single Crystal Superalloy[J],53(1):202-208
Influence of Sand Blasting on Microstructure at Interface of MCrAlY Coating and Single Crystal Superalloy
Received:November 23, 2022  Revised:April 26, 2023
View Full Text  View/Add Comment  Download reader
KeyWord:sand blasting  single crystal superalloy  microstructure evolution  HVOF
GUO Yunshan AECC Commercial Aircraft Engine Co., Ltd., Shanghai , China
WANG Jing AECC Commercial Aircraft Engine Co., Ltd., Shanghai , China
LI Yanyan Institute of Metal Research, Chinese Academy of Sciences, Shenyang , China
BAO Zebin Institute of Metal Research, Chinese Academy of Sciences, Shenyang , China
YUAN Kang BGRIMM Technology Group, Beijing , China
LIU Jianming BGRIMM Technology Group, Beijing , China
Download times:
      Favored by single crystal and γ/γ′ coherent structure, single-crystal superalloys possess extremely high strength and creep/fatigue resistance at high temperature, in which they can be utilized as structural material to fabricatekey hot-sectional components (e.g., blades) in aero or land-based turbine engines. Prior to service at high temperature, the components made by single crystal superalloy are compulsorily deposited with high temperature protective coatings (e.g., MCrAlY) to resist invasions by oxidation and hot corrosion, where a surface blasting is necessarily demanded before the coating procedure. To evaluate the influence of sand blasting on the microstructure change at the interface between the MCrAlY coating and single crystal superalloy, the specimens made of single crystal superalloy were sand blasted with different forces (no, slight or heavy), followed by deposition of the MCrAlY coating using the HVOF method. The purpose of present work is to observe the microstructure change at the coating/substrate interface and investigate the influence of sand-blasting craft on the microstructure evolution. Firstly, the coating samples experienced a typical vacuum treatment to reach homogenization and enhance bonding strength of the coating. After that, they were subject to an oxidation test in a muffle furnace at 1 050 ℃ for 287 h, where the precipitates of topologically close-packed phase (TCP) were observed by SEM under the back-scattered electron (BSE) mode, and the histograms of interdiffusion zone (IDZ) and secondary reaction zone (SRZ) thicknesses were profiled after oxidation. As indicated by the experimental results, a gamma prime depleted zone (GPDZ) was observed at the surface of the substrate for the coating sample right after slight-blasting, where nano scale Mo-rich particles were precipitated inside the GPDZ. After homogenization in vacuum, the substrate area below coating showed formation of IDZ and SRZ, where the IDZ location matched the region of original GPDZ. Below the IDZ, round-shaped TCP precipitates were finely distributed inside SRZ, which were much finer than the bright precipitates existed in IDZ. During oxidation, the total thicknesses of IDZ+SRZ showed approximately a linear rule to the oxidation time, which could be due to the presence of abundant defects in the GPDZ after sand-blasting. Experienced thermal exposure, the needle-like TCP phases were precipitated along 45° direction to the surface in which was the habit orientation of Ni-base single crystal superalloy. Compared withsamples with slightblasting or without blasting, the density and length of TCP precipitates formed in heavyblasting samples after 287 h oxidation were higher. Indeed, the sand blasting process applied a different influence on the thicknesses of IDZ and SRZ:the IDZ thicknesses were comparable (17.5 μm by heavy blasting to 20 μm by slight), but the SRZ thickness with heavy blasting was much higher (52.5 μm to 40 μm). Higher blasting force and larger alumina grits definitely cause severer deformation and destruction to the single crystal superalloy. As sandblasting would induce plastic deformation by forming GPDZ and formation of SRZ (thicker by heavy blasting), it is vitally important to control or reduce the blasting force before depositing a MCrAlY coating on the surface of single crystal superalloy components.