Microstructure and properties of nanostructured YSZ coating prepared by suspension plasma spraying at low pressure

Suspension plasma spraying as a new processing method was employed to deposit nanostructured YSZ coating at a low pressure down to 100 Pa. A nanostructured YSZ powder, a kind of dispersant and ethanol were mixed uniformly prior to conducting the experiment. The axial injection mode was adopted to improve the enthalpy exchange between the plasma jet and sprayed material. The relatively dense coatings were obtained due to the higher velocity of particles accelerated by the relatively higher velocity of the plasma jet at low pressure. The optical emission spectroscopy was used to characterize the nature of the plasma jet and the sprayed YSZ material. The existence of vapor phase of YSZ was demonstrated. The phase and microstructure of the coating were characterized by XRD and SEM, respectively. It is revealed that the crystallite size of as-sprayed coating is reduced from 30 nm for the feedstock to about 20 nm after the thermal spraying process at low pressure. It is also found that the mean value of elastic moduli shows a decreasing tendency from 114.5 to 87.5 GPa with the increase of spraying distance from 150 to 250 mm, whereas the hardness shows a mean value up to 5.77 GPa at a stand-off distance of 200 mm. The hardness and the elastic moduli increase by 61% and 31% in comparison with the obtained values by SPS at atmospheric ambient by previous authors, respectively.