Mechanical Properties of Layered La 2 Zr 2 O 7 Thermal Barrier Coatings
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Mechanical Properties of Layered La2Zr2O7 Thermal Barrier Coatings Xingye Guo1,4 • Li Li2 • Hyeon-Myeong Park3 • James Knapp2 • Yeon-Gil Jung3 Jing Zhang1
•
Submitted: 10 October 2017 / in revised form: 23 December 2017 Ó ASM International 2018
Abstract Lanthanum zirconate (La2Zr2O7) has been proposed as a promising thermal barrier coating (TBC) material due to its low thermal conductivity and high stability at high temperatures. In this work, both single and double-ceramic-layer (DCL) TBC systems of La2Zr2O7 and 8 wt.% yttria-stabilized zirconia (8YSZ) were prepared using air plasma spray (APS) technique. The thermomechanical properties and microstructure were investigated. Thermal gradient mechanical fatigue (TGMF) tests were applied to investigate the thermal cycling performance. The results showed that DCL La2Zr2O7 ? 8YSZ TBC samples lasted fewer cycles compared with single-layered 8YSZ TBC samples in TGMF tests. This is because DCL La2Zr2O7 TBC samples had higher residual stress during the thermal cycling process, and their fracture toughness was lower than that of 8YSZ. Bond strength test results showed that 8YSZ TBC samples had higher bond strength compared with La2Zr2O7. The erosion rate of La2Zr2O7 TBC samples was higher than that of 8YSZ samples, due to the lower critical erodent velocity and fracture toughness of
& Yeon-Gil Jung [email protected] & Jing Zhang [email protected] 1
Department of Mechanical Engineering, Indiana UniversityPurdue University, Indianapolis, IN 46202, USA
2
Praxair Surface Technologies Inc., Indianapolis, IN 46222, USA
3
School of Materials Science and Engineering, Changwon National University, Changwon, Kyungnam 641-773, Republic of Korea
4
College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China
La2Zr2O7. DCL porous 8YSZ ? La2Zr2O7 had a lower erosion rate than other SCL and DCL La2Zr2O7 coatings, suggesting that porous 8YSZ serves as a stress-relief buffer layer. Keywords bond strength erosion lanthanum zirconate thermal barrier coating thermal cycling
Introduction Thermal barrier coating (TBC) materials with low thermal conductivity have been widely used to insulate turbine and engine components from hot gas streams in high-temperature environments (Ref 1). TBC systems typically consist of a superalloy substrate, a metallic bond coat layer, a thermally grown oxide (TGO) layer, and a low-thermalconductivity ceramic top coat. The criteria for TBC material selection include low thermal conductivity, high melting point, high thermal expansion coefficient, good thermal and chemical stability, no phase change, and low sintering activity (Ref 1). Since the maximum surface temperature of commercial 8 wt.% yttrium-stabilized zirconia (8YSZ) TBCs is limited to 1200 °C due to potential sintering and phase change (Ref 2, 3), recently lanthanum zirconate (La2Zr2O7) was proposed as an alternative TBC material for use in higher-temperature applications. Compared with 8YSZ, La2Zr2O7 has lower thermal conductivi
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