Thermal diffusivity and conductivity of yttria stabilized zirconia coatings obtained by suspension plasma spraying

Plasma generated by SG-100 torch was applied to spray suspension formulated with the use of ZrO2 + 8 wt.% Y2O3 (8YSZ) solid phase. The solids have the mean size of about 4.5 μm and were obtained by milling commercial Metco 204NS powder. The suspension was formulated with the use of 20 wt.% of solid phase, 40 wt.% water and 40 wt.% of ethanol. The plasma spray parameters were optimized with the electric power equal to 40 kW, working gases composition Ar—45 slpm and H2—5 slpm, spray distance varying from 40 to 60 mm and torch linear speed with regard to substrate varying from 300 to 500 mm/s. The coatings of the thickness ranging from 51 to 106 μm, were sprayed onto stainless steel substrates. The porosity of the samples was found, with the help of image analysis of metallographically prepared cross-sections of the samples, to be in the range of 8–12%. Thermal diffusivity was measured with the use of the commercial NanoFlash system in the temperature range from room temperature to 523 K. The measurements were made with the use of the coatings sprayed on the substrate and the 2-layers numerical model was applied to determine thermal diffusivity of the coatings. The diffusivity was in the range 0.196 × 10− 6 to 0.352 × 10− 6 m2/s in room temperature depending on the spray parameters. The obtained data were then associated with the literature data on density, specific heat and experimental porosity to find thermal conductivity which was in the range of 0.47 to 0.86 W/(mK) at room temperature depending on the spray run.