Thermal Properties, Thermal Shock, and Thermal Cycling Behavior of Lanthanum Zirconate-Based Thermal Barrier Coatings

Lanthanum zirconate (La 2 Zr 2 O 7 ) coatings are newly proposed thermal barrier coating (TBC) systems which exhibit lower thermal conductivity and potentially higher thermal stability compared to other traditional thermal barrier systems. In this work, La 2 Zr 2 O 7 and 8 wt pct yttria stabilized zirconia (8YSZ) single-layer and double-layer TBC systems were deposited using the air plasma spray technique. Thermal properties of the coatings were measured. Furnace heat treatment and jet engine thermal shock tests were implemented to evaluate coating performance during thermal cycling. The measured average thermal conductivity of porous La 2 Zr 2 O 7 coating ranged from 0.59 to 0.68 W/m/K in the temperature range of 297 K to 1172 K (24 °C to 899 °C), which was approximately 25 pct lower than that of porous 8YSZ (0.84 to 0.87 W/m/K) in the same temperature range. The coefficients of thermal expansion values of La 2 Zr 2 O 7 were approximately 9 to 10 × 10 −6 /K from 400 K to 1600 K (127 °C to 1327 °C), which were about 10 pct lower than those of porous 8YSZ. The double-layer coating system consisting of the porous 8YSZ and La 2 Zr 2 O 7 layers had better thermal shock resistance and thermal cycling performance than those of single-layer La 2 Zr 2 O 7 coating and double-layer coating with dense 8YSZ and La 2 Zr 2 O 7 coatings. This study suggests that porous 8YSZ coating can be employed as a buffer layer in La 2 Zr 2 O 7 -based TBC systems to improve the overall coating durability during service.