Thermal conductivity of plasma-sprayed monolithic and multilayer coatings of alumina and yttria-stabilized zirconia

The temperature dependence of the thermal conductivity of plasma-spray-depo sited monolithic coatings, as well as multilayer coatings that consisted of Al2O3 and ZrO2 that was stabilized by 8% Y2O3 (YSZ), was investigated. The coatings exhibited a large reduction in thermal conductivity at all temper atures, when compared to the bulk monolithic Al2O3 and YSZ. This reduction was due to porosity as well as thermal resistance that was caused by interf aces in the coatings. The largest decrease in the thermal conductivity of t he coatings, relative to monolithic fully dense materials, was due to splat interfaces within each layer, as well as the coating/substrate interface. On the other hand, the multilayer coatings showed little variation in the t hermal conductivity, relative to the number of layers, which suggests that the influence of interlayer interfaces on heat transfer is relatively small . A one-dimensional analysis of steady-state heat transfer has been present ed to illustrate the significance of porosity, splat interfaces, and interl ayer interfaces, with respect to the overall thermal conductivity of multil ayer coatings.