Effects of thermal exposure on microstructure of thermal barriers deposited by hybrid plasma spraying

Hybrid plasma spraying combines plasma spraying of dry powders and liquids (suspensions and solutions). Combination of these two approaches allows deposition of microstructures consisting of both conventional coarse and ultrafine splats. Moreover, splats with dissimilar size may have also different chemistry. Such combination is potentially interesting for many fields of thermal spraying, including thermal barrier coatings, as novel microstructures may be economically obtained. The technology has recently reached a level, where coatings with interesting hybrid microstructures may be reliably deposited, so that their potential for practical applications may be evaluated. In order to evaluate annealing/sintering resistance of the hybrid TBC coatings, TBCs with YSZ-based hybrid top-coat were deposited by hybrid water/argon stabilized plasma (WSP-H) technology. Then, samples were exposed to elevated temperatures simulating in-service conditions and changes of the coatings microstructure were studied by high-resolution scanning electron microscopy with EDS mapping, image analysis and X-ray diffraction.