Healing of the Interface Between Splashed Particles and Underlying Bulk Coating and Its Influence on Isothermal Oxidatio
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Bang-Yan Zhang, Jing Shi, Guan-Jun Yang, Cheng-Xin Li, and Chang-Jiu Li (Submitted June 6, 2014; in revised form December 22, 2014) The thermally grown oxide formed on the bond coat surface plays an important role in determining the lifetime of thermal barrier coatings (TBCs). The splashed particles on the thermally sprayed MCrAlY bond coat surface are weakly bonded to the underlying bulk coating, leading to the formation of mixed oxides and contributing to the TBC failure. In this study, the healing behavior of the weakly bonded interface between splashed particles and underlying MCrAlY bulk coating deposited by low pressure plasma spraying was examined, and the influence of interface healing on the isothermal oxidation behavior of the bond coat was discussed. Results show that the granular particles resulting from splashing of molten droplets were exposed on smooth splats which make up the surface of bulk coating. After the pre-diffusion treatment in vacuum, the small granular splashed particles are immersed into the bulk coating resulting from the element diffusion on the interface between splashed particles and underlying bulk coating. After the vacuum heat treatment, the formation of mixed oxides was effectively restrained due to the healing of the splashed particle/underlying bulk coating interface.
Keywords
bond coat, interface healing, isothermal oxidation, splashed particles, thermal barrier coatings
1. Introduction Thermal barrier coatings (TBCs) have been widely applied to hot section parts in gas turbines for both aircraft engines and industrial electric power generation (Ref 1-4). TBCs are generally composed of a thermal insulating yttria-stabilized zirconia (YSZ) top coating and a MCrAlY bond coat on a Ni-based superalloy substrate. A thermally grown oxide (TGO), which grows at the interface between the bond coat and the YSZ coating, is actually an additional part of TBCs (Ref 5-7). It is reported that the TGO plays an extremely important role in determining the lifetime of TBCs (Ref 1, 8). The preparation approach of MCrAlY bond coat and its microstructure is closely related with the durability of This article is an invited paper selected from presentations at the 2014 International Thermal Spray Conference, held May 21-23, 2014, in Barcelona, Spain, and has been expanded from the original presentation. Bang-Yan Zhang, Jing Shi, Guan-Jun Yang, Cheng-Xin Li, and Chang-Jiu Li, State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, XiÕan Jiaotong University, XiÕan 710049, Shaanxi, PeopleÕs Republic of China. Contact e-mails: [email protected] and [email protected]. edu.cn.
Journal of Thermal Spray Technology
the thermal insulating top coating. For atmospheric plasma-sprayed (APS) YSZ top coating, a rough bond coat surface is required to create a better interlocking adhesion. However, such interface morphology produces the out-of-plane stresses responsible for in-service failure (Ref 9), since the out-of-plane stress due to the undulating bond coat su
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