Microstructure of yttria stabilized zirconia deposited by plasma spraying

A thick deposit of yttria stabilized zirconia (YSZ) was fabricated by inductively coupled plasma spraying and its microstructure was investigated. During solidification the solute rejection occurred in the layers, but the interface condition of (dTq/dz)z=0>m(dC/dz)z=0 led to the formation columnar grains. In the middle part different to the other parts, large columnar grains, approximately 100 μm thick and 300 μm long, were developed through the layers with a strong adhesion. The heat of the droplets, the latent heat of the solidification, and a low thermal conductivity delay the heat transfer, and favor the growth of long columnar grains. The long columnar grain growth through the layers is supposed to be possible, when the previously solidified surface of the deposit acts as a seed.