Plasma-Sprayed Thermal Barrier Coatings with Enhanced Splat Bonding for CMAS and Corrosion Protection
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ao Liu, Shu-Wei Yao, Li-Shuang Wang, Guan-Jun Yang, Cheng-Xin Li, and Chang-Jiu Li (Submitted May 23, 2015; in revised form September 30, 2015) The infiltration of molten CMAS in thermal barrier coatings (TBCs) at high temperature is significantly affected by the microstructure of the ceramic coating. Enhancing the bonding ratio between splats can reduce the interconnected pores and suppress the infiltration of the molten CMAS into the coating. In this study, a dual-layered (DL) TBC with the dense 8YSZ on the top of the conventional porous 8YSZ was proposed to enhance CMAS corrosion of atmospheric plasma-sprayed YSZ. The dense YSZ coating with improved lamellar bonding was deposited at a higher deposition temperature. The microstructure of the coatings before and after CMAS attack test was characterized by scanning electron microscopy. It was clearly revealed that by adjusting the microstructure and applying a dense ceramic layer with the improved interface bonding on the top of porous TBC, the infiltration of CMAS into porous YSZ coating can be effectively suppressed. Moreover, by designing DL TBCs, the thermal conductivity of the TBC system exhibits a limited increase. Thus with the design of DL structure, the TBCs with high CMAS corrosion resistance and low thermal conductivity can be achieved.
Keywords
atmospheric plasma spraying, CMAS, corrosion resistance, interface bonding
1. Introduction Thermal barrier coatings (TBCs) are widely applied to protect the metal substrate of the hot section components of gas turbine. TBC system is usually composed of a ceramic top coat as thermal insulation layer with low thermal conductivity, a metallic bond coat (BC, MCrAlY, M=Ni/Co). Moreover, the ceramic top coat is usually fabricated by either electron beam physical deposition (EB-PVD) or atmospheric plasma spraying (APS). Currently, zirconia containing 6-8 wt.% of yttria (8YSZ), which exhibits low thermal conductivity and excellent mechanical properties, is used as standard material of ceramic top coat of TBCs (Ref 1-3). Generally, the performance of TBCs includes two important aspects: thermal insulation ability and life duration during thermal cycle. TBCs are designed to reduce the temperature of the metallic substrate. Therefore, low This article is an invited paper selected from presentations at the 2015 International Thermal Spray Conference, held May 11-14, 2015, in Long Beach, California, USA, and has been expanded from the original presentation. Tao Liu, Shu-Wei Yao, Li-Shuang Wang, 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, China. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
thermal conductivity is essential for TBCs. For certain ceramic materials, by choosing different deposition approaches and adjusting the deposition parameters, the coatings with different microstructures and consequently different properties including the thermal conduct
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