(Office of the Vice Chancellor for Research, 2016-04-08) Guo, Xingye; Jung, Yeon-Gil; Li, Li; Knapp, James; Zhang, Jing
Abstract
La2Zr2O7 is a promising thermal barrier coating material due to its low thermal conductivity and superior high temperature stability. In this work, La2Zr2O7 and conventional 8 wt% yttria stabilized zirconia (8YSZ) coatings were deposited using plasma spray technique. Both singlelayer La2Zr2O7 and double-layer 8YSZ/La2Zr2O7 coating architectures were designed. Thermal conductivity and coefficients of thermal expansion (CTE) of the coatings were measured. The measured average thermal conductivity of La2Zr2O7 was about 25% lower than that of porous 8YSZ. The CTE values of La2Zr2O7 were about 10% lower than that of 8YSZ. Thermal cycling and thermal shock tests were used to evaluate coatings’ thermomechanical properties. All La2Zr2O7 coats were delaminated in the furnace cycle test in less than 20 cycles. This is because residual thermal stresses accumulated during thermal cycling. In the jet engine thermal shock (JETS) tests, the single-layer La2Zr2O7 and double-layer dense 8YSZ/La2Zr2O7 coatings were fully delaminated. In contrast, the double-layer porous 8YSZ/La2Zr2O7 coating sample only partially delaminated on the edge. This is because the porous 8YSZ layer provides strain compliance. The findings will help to propose efficient thermal barrier coating systems.