Fabrication and characterization of 7.5 wt% Y₂O₃-ZrO₂ thermal barrier coatings deposited by suspension plasma spray

Considerable research efforts have been explored attempting to enhance the thermal durability of thermal barrier coatings (TBCs) at the high operating temperatures of gas turbines. In this study, the suspension plasma spray (SPS) process was applied to produce TBCs with a segmented structure by using an yttria-stabilized zirconia (YSZ) suspension. Four different experiment sets were carried out by controlling the ratio between surface roughness of the bond coat and feed stock size (R_a/D₅₀) in order to examine the effect of R_a/D₅₀ ratio on the microstructure of SPS-prepared coatings. When the R_a/D₅₀ had a high value of 11.8, a deposited thick coating turned out to have a cone-type columnar microstructure. In contrast, at the low R_a/D₅₀ values of 2.9 and 0.18, a deposited thick coating appeared to have a dense, vertically-cracked microstructure. However, with the very low R_a/D₅₀ value of 0.05 the coating was delaminated.