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.
During the last decade a number of ceramic materials, mostly oxides have been suggested as new thermal barrier coating (TBC) materials. These new compositions have to compete with the state-of-the-art TBC material yttria stabilized zirconia (YSZ) which turns out to be difficult due to its unique properties. On the other hand YSZ has certain shortcomings especially its limited temperature capability above 1200 °C which necessitate its substitution in advanced gas turbines. In the paper an overview is tried on the different new materials covering especially doped zirconia, pyrochlores, perovskites, and aluminates. Literature results and also results from our own investigations will be presented and compared to the requirements. Finally, the double layer concept, a method to overcome the limited toughness of new TBC materials, will be discussed.
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