Epitaxial growth during the rapid solidification of plasma-sprayed molten TiO₂ splat

In this study, epitaxial growth during the rapid solidification of plasma-sprayed molten TiO₂ droplet was studied. The crystallographic structure of the TiO₂ splats deposited on rutile and α-Al₂O₃ substrates at 150, 300 and 500 °C was characterized by high resolution transmission electron microscopy and electron back scattering diffraction. The results reveal that homo-epitaxial and hetero-epitaxial TiO₂ splats can be formed at the deposition temperature of 500 °C. Crystal orientation is another key factor influencing the epitaxial growth process. It is easier to form an epitaxial TiO₂ splat with the 〈001〉 orientation in the crystal growth direction. Based on the experimental results, a competition mechanism between heterogeneous nucleation and epitaxial growth was proposed to understand the phenomena of epitaxy during the rapid solidification process. The effect of undercooling degree, crystal orientation and deposition temperature on the epitaxial growth of TiO₂ splat was examined. The simulation results are in close agreement with the experimental observations.