New Thermal Barrier Coatings Based on Pyrochlore/YSZ Double‐Layer Systems

Pyrochlore materials La ₂ Zr ₂ O ₇ and Gd ₂ Zr ₂ O ₇ have been used to produce thermal barrier coating systems by atmospheric plasma spraying. The materials have been applied as single‐layer coatings with only a topcoat made of pyrochlore material. In addition, double‐layer systems with a first layer of yttria‐stabilized zirconia (YSZ) and a top layer made of pyrochlore material were produced. These systems have been tested in thermal cycling test rigs at surface temperatures between 1200‐1450°C and the results were compared to the behavior of YSZ coatings. Single‐layer coatings had a rather poor thermal cycling performance. On the other hand, double‐layer systems showed similar results to YSZ coatings at temperatures below about 1300°C. At higher temperatures the double‐layer coatings produced from our own powders revealed excellent thermal cycling behavior. At the highest test conditions, lifetime was thereby orders of magnitude better than that of YSZ coatings. Results indicate that an increase of the maximum surface temperature in gas turbines by at least 100 K becomes possible with the new coatings. Coatings produced from commercial powders showed a somewhat reduced performance.