Zirconates as New Materials for Thermal Barrier Coatings

Abstract

Zirconates with high melting points were investigated for application as materials for thermal barrier coatings at operating temperatures >1300°C. SrZrO 3 , BaZrO 3 , and La 2 Zr 2 O 7 powders were synthesized and sintered to compacts with various levels of porosity. The sintering results indicated a promising low‐sintering activity of the investigated materials. Thermal properties of these dense materials were determined. Thermal expansion coefficients were slightly lower than those of Y 2 O 3 ‐stabilized ZrO 2 (YSZ); thermal conductivities of SrZrO 3 and BaZrO 3 were comparable or slightly higher than those of YSZ. La 2 Zr 2 O 7 had a lower thermal conductivity. SrZrO 3 was not suitable for application as a thermal barrier coating because of a phase transition at temperatures between 700° and 800°C. Mechanical properties (hardness, fracture toughness, and Young's modulus) of dense BaZrO 3 and La 2 Zr 2 O 7 samples were determined by indentation techniques and showed lower hardness and Young's modulus compared to YSZ. BaZrO 3 and La 2 Zr 2 O 7 powders were optimized for application as powders for plasma spraying. Plasma‐sprayed coatings were produced and characterized. Thermal cycling with a gas burner at 1200°C showed a massive attack of the BaZrO 3 coating, with loss of BaO. On the other hand, the La 2 Zr 2 O 7 coating showed excellent thermal stability and thermal shock behavior.