Thermal Properties of Plasma-Sprayed Multilayer Al₂O₃/Yttria-Stabilized Zirconia Coating.

Yttria-stabilized zirconia (YSZ) and Al₂O₃ multilayer coatings were fabricated by plasma spraying. Thermal conductivity and thermal shock test were investigated to find out the thermal properties of the coating layer and the surface of the crack. Thermal conductivity was investigated using laser flash method and thermal shock were measured by water quenching method. Furthermore, the factors influencing thermal properties of these coatings were analyzed in detail. Multilayer coatings have imperfect interfaces. At an imperfect interface, the heat transfer coefficient was close to zero, indicating a low thermal conductivity. Multilayer coatings increase thermal shock resistance. This is because ZrO₂ phases transformation from tetragonal to monoclinic occurring to the cooling process, resulting in microcracks due to volume expansion. The crack generated at this time dispersed and absorbed the thermal shock, so that it exhibited excellent thermal shock resistance.