Long‐Term Behavior and Application Limits of Plasma‐Sprayed Zirconia Thermal Barrier Coatings

<jats:p>Investigations of changes in phase composition, mechanical properties, and microstructure of ZrO<jats:sub>2</jats:sub>‐based plasma‐sprayed thermal barrier coatings (TBCs) with 8 mol% CeO<jats:sub>2</jats:sub>, 19.5 mol% CeO<jats:sub>2</jats:sub>/1.5 mol% Y<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>, 35 mol% CeO<jats:sub>2</jats:sub>, and 4.5 mol% Y<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> after long‐term heat treatments at typical operation temperatures (1000°–1400°C) are presented. Experimental studies include X‐ray diffractometry, mechanical testing, and scanning electron microscopy. Thermal cycling experiments also have been performed. TBCs with 8 mol% CeO<jats:sub>2</jats:sub> contain mainly the tetragonal equilibrium phase and, therefore, show rapid failure because of the high amount of tetragonal → monoclinic phase transformation, even after relatively short heat treatments (1250°C/1 h). In the case of the other systems that consist mainly of the tetragonal or cubic nonequilibrium phases, TBCs with 19.5 mol% CeO<jats:sub>2</jats:sub>/1.5 mol% Y<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> or 35 mol% CeO<jats:sub>2</jats:sub> reveal a smaller amount of monoclinic phase after long‐term heat treatments (1250°C/1000 h) compared with TBCs containing 4.5 mol% Y<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>. TBCs containing 35 mol% CeO<jats:sub>2</jats:sub> show a higher degree of sintering than the TBCs with 19.5 mol% CeO<jats:sub>2</jats:sub>/1.5 mol% Y<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> and, therefore, a greater increase of the elastic modulus. Among the systems investigated, TBCs containing 4.5 mol% Y<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> exhibit the highest resistance to failure in thermal‐cycling experiments.</jats:p>