Investigations of changes in phase composition, mechanical properties, and microstructure of ZrO 2 -based plasma-sprayed thermal barrier coatings (TBCs) with 8 mol% CeO 2 , 19.5 mol% CeO 2 /1.5 mol% Y 2 O 3 , 35 mol% CeO 2 , and 4.5 mol% Y 2 O 3 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 2 contain mainly the tetragonal equilibrium phase and, therefore, show rapid failure because of the high amount of tetragonal 3 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 2 /1.5 mol% Y 2 O 3 or 35 mol% CeO 2 reveal a smaller amount of monoclinic phase after long-term heat treatments (1250°C/1000 h) compared with TBCs containing 4.5 mol% Y 2 O 3 . TBCs containing 35 mol% CeO 2 show a higher degree of sintering than the TBCs with 19.5 mol% CeO 2 /1.5 mol% Y 2 O 3 and, therefore, a greater increase of the elastic modulus. Among the systems investigated, TBCs containing 4.5 mol% Y 2 O 3 exhibit the highest resistance to failure in thermal-cycling experiments.
Epitaxial, continuous, approximately 40-nm-thick films of SrZrO3 on SrTiO3 substrates prepared by a chemical solution deposition method including a postdeposition heat treatment at 900–1000 °C were subjected to further heat treatments at higher temperatures (approximately 1200–1300 °C) to investigate their high temperature stability. Experimental investigations included scanning electron microscopy, atomic force microscopy, and conventional transmission electron microscopy. The investigations have demonstrated a morphological instability of the films. Concentration profiles of the cations determined by energy dispersive x-ray spectroscopy, as well as investigations by x-ray diffraction, revealed that the film islands consisted of a solid solution. As shown by high-resolution electron microscopy, the reaction between film and substrate also led to an increase in the separation distance of the misfit dislocations that were introduced during the lower temperature heat treatment to relax the lattice mismatch strain. The morphological and structural changes of the films are reported and discussed in this paper.
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