Mechanism of Competitive Grain Growth in 8YSZ Splats Deposited by Plasma Spraying

The competitive growth mechanism of columnar grains generated from rapid solidification in plasma-sprayed yttria-stabilized zirconia (YSZ) splats collected on stainless steel at different temperatures was studied. The microstructure of YSZ splats was examined quantitatively by scanning electron microscope and x-ray diffraction. The crystalline orientation of columnar grains was investigated by electron backscattered diffraction. It was found that the competition between the columnar grains was governed by their relative growing rate. The columnar grains with growing face (001) had the slowest growing rate, while those with growing face {011} had the fastest growing rate. The degree of competition between the columnar grains was related to the nucleation rate for the splat at different substrate temperatures (T (s)). When the splat was at T (s) = 300 K or T (s) = 373 K, the relatively low nucleation rate resulted in less competition between the columnar grains; thus, no preferential orientation was observed. In contrast, for the splat at T (s) = 473 K, the higher nucleation rate resulted in more competition between the columnar grains, increasing the proportion of grains with the faster growing face {011}, and therefore, the columnar grains show aOE (c) 011 > preferential orientation.