Effect of splat morphology on the microstructure and dielectric properties of plasma sprayed barium titanate films

Abstract

In the thermal spray process, the film is built up by impingement of molten droplets onto substrate. Splats are created by flattening and spreading of the impacting droplets. Splat morphology can determine the microstructure, physical and mechanical properties of the coating. In this study, BaTiO3 films were deposited onto a mirror polished stainless steel substrates kept at three different temperatures (25, 300 and 600°C). At the elevated temperatures, the substrate surface topography and the desorbtion of adsorbates and condensate at the substrate surface are two important factors which change the morphology of the individual splats, from splash morphology to disk-like shape. Splat morphology can determine deposit microstructure and improve the coating properties. The morphology of individual splats and the films were studied using scanning electron microscopy. Phase formation of the films was analyzed by X-ray diffraction. The surface topography of the substrates with different temperatures was analyzed using atomic force microscopy. Furthermore, X-ray photoelectron spectroscopy was performed to determine the chemical compositions of the surface substrate. Results indicated that the porosity in the film produced at room temperature was higher than that in the film deposited on the heated substrates. Also, the dielectric coefficient of the films was increased by decreasing the common defects from 120 to 505 for film deposited on as-received and heated substrates, respectively.