Characterization of microstructure and thermal properties of YCSZ coatings obtained by suspension plasma spraying

• The thermal transport properties of yttria/ceria stabilized zirconia coatings were studied.
• Suspension plasma spraying method was used to produce coatings.
• Process parameters have influence on suspension plasma sprayed coating microstructure.
• Coatings were characterized by a typical two-zone microstructure.
• Low thermal conductivity value was caused by relatively high micro-porosity of coatings.

The paper describes the procedure of determination of thermal properties (thermal diffusivity and thermal conductivity) of yttria/ceria stabilized zirconia coatings. The coatings were deposited by suspension plasma spraying method using SG-100 torch. The commercial powder with a chemical composition ZrO2 + 24 wt.% CeO2 + 2.5 wt.% Y2O3 was used and coatings were sprayed onto stainless steel substrates. The suspensions consisted of zirconia powder, water, ethanol and small addition of dispersant. The design of spray experiments included the following variable process parameters: (i) spray distance; and (ii) torch scan linear speed. The microstructure of coatings was determined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The phase composition and the crystallite size of coatings were estimated by Rietveld method. The different methods were used to find out the thermal properties values up to 573 K. Firstly, thermal diffusivity of YCSZ coatings was determined by using a commercial setup and the obtained results were used to calculate the values of thermal conductivity. Then, to check the validity of the measurements and calculations, the simulations of laser flash experiment were made using COMSOL Multiphysics software. The least square method enabled to find the optimized value of thermal conductivity. Finally, the use of another setup enabled to find out the thermal transport properties in the temperature up to 873 K.