Preliminary study on suspension plasma sprayed ZrO2 + 8 wt.% Y2O3 coatings

ZrO2 + 8 wt.% Y2O3 powder of a mean diameter dVS = 38 μm was milled to obtain fine particles having mean size of dVS = 1 μm. The fine powder was used to formulate a suspension with water, ethanol and their mixtures. The zeta potential of obtained suspensions was measured and found out to be in the range from −22 to −2 mV depending on suspension formulation. The suspension was injected through a nozzle into plasma jet and sprayed onto stainless steel substrates. The plasma spray experimental parameters included two variables: (i) spray distance varying from 40 to 60 mm and (ii) torch linear speed varying from 300 to 500 mm/s. The microstructure of obtained coatings was characterized with scanning electron microscope (SEM) and X-ray diffraction (XRD). The coatings had porosity in the range from 10% to 17% and the main crystal phase was tetragonal zirconium oxide. The scratch test enabled to find the critical load in the range of 9–11 N. Finally, thermal diffusivity of the samples at room temperature, determined by thermographic method, was in the range from 2.95 × 10−7 to 3.79 × 10−7 m2/s what corresponds to thermal conductivities of 0.69 W/(mK) and 0.97 W/(mK) respectively.