Columnar grain growth of Yttria-stabilized-zirconia in inductively coupled plasma spraying

Abstract

Yttria-stabilized-zirconia (YSZ) was deposited 7 mm thick by inductively coupled plasma spraying (ICP) and a theory of nucleation and solidification of YSZ was introduced. The concentration was homogeneous within a particle, but different from particle to particle. The solute rejection by diffusion occurred in a layer during solidification, but the interface condition of (dT(q)/dz)(z=0) > m(dC/dz)(z=0) led columnar grains to facilitate. The microstructure of the bottom part showed small equiaxed grains. In the middle part, large columnar grains, about 100 mum thick and 300 mum long, were developed through the layers with strong adhesion. Heat of droplets, latent heat of solidification, small pore array in the splat boundaries, and low thermal conductivity retard the heat transfer, and thus thick and long columnar grains could be facilitated. The long columnar grain growth through the layers was supposed to be possible when the previously solidified surface of the deposit acts as seed.