An aqueous nitrate-based precursor solution was deposited on stainless steel substrate by spray pyrolysis to produce thick lanthanum zirconate coatings for thermal barrier coating application. The as-deposited, dried, and further annealed coatings were characterized by thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The influence of the substrate temperature on the film formation and microstructure has been carefully studied for a better understanding of the deposition mechanisms. A temperature range corresponding to the deposition of an ionic salt liquid was found to be critical to obtain thick crack-free green coatings. Further heat treatment was necessary to decompose the nitrate species into an oxide coating with a fine porous microstructure.

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Cracks should normally be avoided in the deposition of coatings, but vertical cracks in thermal barrier coatings are engineered to absorb thermo‐mechanical stress. Thick lanthanum zirconate coatings were deposited by spray pyrolysis deposition from aqueous nitrate‐based precursor solutions, and cracks were formed during decomposition of the nitrate species due to the associated volume change. The crack spacing and crack opening in the deposited coatings were analyzed in terms of thickness, pH of the precursor solution, and deposition and decomposition temperatures and kinetics by thermogravimetry, scanning calorimetry, mass spectroscopy, and electron microscopy. The thickness of the coatings demonstrated the most important effect on the crack pattern. The crack opening and the crack spacing varied linearly with increasing thickness, leading to small delamination at the interface. The cracks were stable after the crystallization of the films by further heat treatment. Knowing the influence of the different parameters, coatings with a designed crack pattern can be deposited.

Vertical cracks are beneficial in thermal barrier coatings due to enhanced thermomechanical compliance. Accordingly, an aqueous nitrate based precursor solution was atomized on stainless steel substrates by spray pyrolysis to deposit thick crack-designed lanthanum zirconate coatings. Coatings with designed crack patterns were deposited and characterized by electron microscopy, tribology, Vickers indentation, and thermal diffusivity. The crystallization of the coatings was investigated by in situ high temperature X-ray diffraction. The green coatings crystallized from 600 °C and the pyrochlore structure was formed after heat treatment at 1000 °C. Crystalline lanthanum zirconate multilayered coatings with small crack spacing and crack opening exhibited a higher density, a higher hardness, lower thermal diffusivities, and higher thermal conductivities compared to crystalline monolayered coatings of similar thickness with large crack spacing and crack opening. The thermal diffusivity of the coatings, ~28 mm 2 /s at room temperature, was similar to the values reported for yttria-stabilized zirconia plasma sprayed coatings.