Perovskite-type strontium zirconate as a new material for thermal barrier coatings

Perovskite-type SrZrO3 was investigated as an alternative to yttria-stabilized zirconia (YSZ) material for thermal barrier coating (TBC) applications. Three phase transformations (orthorhombic <-> pseudo-tetragonal <-> tetragonal <-> cubic) were found only by heat capacity measurement, whereas the phase transformation from orthorhombic to pseudo-tetragonal was found in thermal expansion measurements. The thermal expansion coefficients (TECs) of SrZrO3 coatings were at least 4.5% larger than YSZ coatings up to 1200 degrees C. Mechanical properties (Young's modulus, hardness, and fracture toughness) of dense SrZrO3 showed lower Young's modulus, hardness, and comparable fracture toughness with respect to YSZ. The steady-state sintering rate of a SrZrO3 coating at 1200 degrees C was 1.04 x 10(-9) s(-1), which was less than half that of YSZ coating at 1200 degrees C. Plasma-sprayed coatings were produced and characterized. Thermal cycling with a gas burner showed that at operating temperatures similar to 1250 degrees C the cycling lifetime of SrZrO3/YSZ double-layer coating (DLC) was more than twice as long as SrZrO3 coating and comparable to YSZ coating. However, at operating temperatures > 1300 degrees C, the cycling lifetime of SrZrO3/YSZ DLC was comparable to the optimized YSZ coating, indicating SrZrO3 might be a promising material for TBC applications at higher temperatures compared with YSZ.