Phase stability of plasma sprayed YAG–YSZ composite beads/coatings at high temperature

Beads and coatings of YAG–YSZ composite ceramic were prepared by plasma spray. YAG was applied as an additive in the hope of improving the phase stability and oxygen impermeability of YSZ. To achieve this aim, some basic research about crystallization behavior and chemical compatibility of the composite were carried out. Plasma sprayed YAG tended to form amorphous state. With the different content of YAG in the composite, crystallization of YAG and YSZ was delayed by each other to different extent due to the barrier effect of heavy atoms. The relative low melting point of YAG led to dense coatings without obvious splat structure and further distinctive vertical cracks during crystallization within the coatings. The cracks became less severe when YAG content was lower. With the addition of YAG, the development of monoclinic ZrO2 was suppressed while Y-rich phases were promoted at higher temperature.