Crack engineering in thick coatings prepared by spray pyrolysis deposition

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.