Microcrack formation in plasma sprayed thermal barrier coatings

Air plasma sprayed ZrO2–8wt%Y2O3 thermal barrier coatings were deposited under tightly controlled conditions. The lengths and orientations of the horizontal cracks and vertical cracks in these coatings were characterized in detail, and process/structure maps of the crack distribution as a function of particle and substrate states were constructed. A fully coupled thermo-mechanical finite element model was used to study the buildup of stresses during splat solidification, and to understand the effect of deposition conditions on crack formation during plasma spray deposition. The model also showed that surface roughness plays a key role in determining the magnitude of maximum stresses, and that only roughness features on the scale of splat thickness are important in providing locations of maximum stress concentration.