A study of the microstructure of yttria-stabilized zirconia deposited by inductively coupled plasma spraying

Zirconia stabilized with 20 wt.% yttria was deposited to a thick free-stand ing type, similar to7 mm, by (inductively coupled plasma spraying) (ICPS), The spheroidization of particles and the microstructure of deposits were an alyzed. Spheroidization fraction dependence on spray parameters such as par ticle size, H-2 gas mixing quantity, and probe position was studied. Effect s of parameters on the spheroidization of particles were analyzed by ANOVA (analysis of variance) (ANOVA). ANOVA results showed that the spheroidizati on fraction largely depend on H-2 gas mixing quantity and particle size, an d there are also some dependence on probe position and H-2 gas mixing quant ity. After melting, particles kept their chemical composition homogeneously from the center to their surface without segregation or evaporation. The d egree of deformation of the diameter of the splat over the diameter of the spheroidized particle was approximately 320% and splat thickness in the dep osit varies between 2 mum and 3 mum depending on the deposition condition. The yttrium concentration gradient of the interlayer boundary appeared line ar in the range of 0.5 to 1 mum. X-ray diffraction analysis and a transmiss ion electron microscope (TEM) micrograph showed that low yttrium content pa rticles resulted in tetragonal phase in deposit. The major characteristics of the microstructure of the thick free-standing deposit and solidification mode were studied. Microstructure of the bottom part of the deposit repres ented equiaxed or cellular structure. Equiaxed small grains prevailed when the droplets were quenched rapidly on substrate. The middle part of the dep osit showed large columnar grains, of about 100 mum thick and 300 mum long. This may be due to high substrate or deposit temperatures and results in r ecrystallization and grain growth. The effects of the parameters, such as H-2 gas mixing quantity, particle si ze, spraying distance, and probe position, on the microstructure of the dep osits were evaluated. The H-2 gas mixing quantity of Ar/H-2 = 120/20 L/min compared to Ar/H-2 = 120/10 L/min resulted in larger grain size and thicker cellular in chill. Grain shapes were affected by the heat removal rate fro m the deposit to its surrounding. Deposition with larger particle size show ed heterogeneous grain size, insufficient particle melting, and incomplete recrystallization, The effect of probe position was less than the others.