Macrocrack formation in plasma-sprayed YSZ TBCs when spraying thick passes

The aim of this work is to study the formation of macrocracks orthogonal to the substrate in yttria-stabilised zirconia coatings, deposited in one or two thick passes (more than a hundred gm each), by a direct current (DC) plasma torch. Zirconia was air plasma sprayed on Hastelloy X substrates, with a NiCrAlY bond coat. The different parameters, which control this phenomenon, are considered through a statistical approach. A special attention is devoted to the quenching stress during deposition. A particular resulting microstructure with columnar zirconia grains is presented. A search of the most influent spray parameters has also been conducted.