Thermomechanical properties of novel lanthanum zirconate based thermal barrier coatings an integrated experimental and modeling study
Guo, Xingye. Ph.D. Purdue University, December 2016. Thermomechanical Properties of Novel Lanthanum Zirconate Based Thermal Barrier Coatings An Integrated Experimental and Modeling Study. Major Professors: Jing Zhang, School of Engineering and Technology and Yung C. Shin, School of Mechanical Engineering. Thermal barrier coatings (TBCs) are refractory materials deposited on gas turbine components, which provide thermal protection for metallic components at operating conditions. The current state of art TBC material is yttria stabilized zirconia (YSZ) whose service temperature is limited to 1200 *C, due to sintering and phase transition at higher temperatures. In comparison, lanthanum zirconate (La2Zr2O7, LZ) has become a promising candidate material for TBCs due to its lower thermal conductivity and higher phase stability compared to YSZ. The primary objective of this thesis is to design a novel robust LZ based TBC system suitable for applications beyond 1200 *C. Due to LZ' s low coefficient of thermal expansion and fracture toughness, which cause poor thermal cycling performance, two TBC architectures are proposed: (1) multiple layered coating, and (2) LZ/8YSZ composite coating. In this work, LZ powders are fabricated using the solid state reaction method, and all of the coatings are deposited using air plasma spray (APS) technique. The physical, thermal and mechanical properties of the sprayed LZ coatings have been systematically investigated, including temperature dependent thermal conductivity, coefficient of thermal expansion, density, hardness, Young' s modulus, bond strength, and erosion resistance. The durability of the coatings in various thermal and mechanical conditions is also investigated, including furnace cycling test, thermal gradient mechanical fatigue test, and jet engine thermal shock test. The results show that for the layered TBCs, porous YSZ LZ has reasonably good thermal cycling perfor