Thermal Diffusivity 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 solid phase. The solids have the mean size of about 4.5 µm and were obtained by milling of commercial Metco 204 NS 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 scan linear speed varying from 300 to 500 mm/s. The coatings of the thickness ranging from 30 to 110 µm, were sprayed onto stainless steel substrates. The porosity of the samples was found from the image analysis of metallographically prepared cross-sections of the samples to be in the range of 7 – 8 %. Thermal diffusivity was measured with the use of the commercial NanoFlash system in the temperature range from room temperature to 300°C. The measurements were made with the use of the coatings sprayed on the substrate and the 2-layers numerical model was developed to determine thermal diffusivity of the coatings. The obtained data were then associated with the literature data of density and specific heat and experimental porosity to find thermal conductivity which was in the range of 0.5 to 1.7 W/(mK) depending on the spray run.