Incorporation of various SiC healing agents into YSZ thermal barrier coatings by using hybrid and intermixed plasma spraying concepts – microstructural investigations

One of the important trends in thermal spraying assumes using various types of feedstock materials, like powders, suspensions, solutions, or spray processes at once. In this work, the so-called hybrid and intermixed plasma spraying concepts were used to incorporate SiC-based healing agents into the YSZ top coat matrix.

The nanometer-sized and submicrometer-sized SiC particles as well as the SiC whiskers were tested as potential self-healing agents for YSZ-based TBCs. The top coat deposition route involved the use of YSZ solution precursor, ready-to-spray suspension, and commercially available spray-grade powder. Then, by simultaneous or sequential feeding, the reliability of hybrid and intermix concepts to incorporate various healing agents as a secondary phase in the YSZ matrix was studied. The TBC specimens were characterized for microstructure by scanning electron microscopy (SEM/EDS) and phase constitution by X-ray diffraction (XRD) along with the quantitative evaluation of the SiC content in the coating.

The microstructural investigations revealed that the introduction of various SiC particles is possible by both, intermixed and hybrid concepts. Depending on the spray process of the primary YSZ phase, it was possible to harness the benefits of finely grained microstructures by SPPS or SPS processes or the desirable efficiency by APS method.