Zirconates as new materials for thermal barrier coatings

Zirconates with high melting points were investigated for application as ma terials for thermal barrier coatings at operating temperatures >1300 degree s C. SrZrO3, BaZrO3, and La2Zr2O7 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 pr operties of these dense materials were determined. Thermal expansion coeffi cients were slightly lower than those of Y2O3-stabilized ZrO2 (YSZ); therma l conductivities of SrZrO3 and BaZrO3 were comparable or slightly higher th an those of YSZ. La2Zr2O7 had a lower thermal conductivity. SrZrO3 was not suitable fur application as a thermal barrier coating because of a phase tr ansition at temperatures between 700 degrees and 800 degrees C. Mechanical properties (hardness, fracture toughness, and Young's modulus) of dense BaZ rO3 and La2Zr2O7 samples were determined by indentation techniques and show ed lower hardness and Young's modulus compared to YSZ. BaZrO3 and La2Zr2O7 powders were optimized for application as powders for plasma spraying. Plas ma-sprayed coatings were produced and characterized, Thermal cycling with a gas burner at 1200 degrees C showed a massive attack of the BaZrO3 coating , with loss of BaO. On the other hand, the La2Zr2O7 coating showed excellen t thermal stability and thermal shock behavior.