A high pressure, electron-beam directed-vapor deposition process has been used to deposit partially stabilized zirconia containing 7 % yttria by mass at deposition pressures of 7.5 Pa to 23 Pa. Anisotropic ultra-small-angle X-ray scattering (USAXS) was then used to determine the surface area, shape and orientation of pores with a diameter between 2 μm and 50 nm (with an opening dimension down to 10 nm). The total surface area of the ellipsoidal shaped pores was found to increase with deposition pressure. However, the through-thickness thermal conductivity measurements reveal the existence of a minimum thermal conductivity in coatings deposited at an intermediate pressure. Observations of the anisotropic X-ray scattering intensity at this intermediate pressure indicated greater proportions of both feather-like (oblate) pores with their major dimension at about 60° to the plane of the coating and fine columnar (prolate) pores oriented perpendicular to it. Since these oblate pore orientations are most efficient at impeding conductive thermal transport through the coating, it is believed that the change in preferred pore orientations with pressure are responsible for the higher thermal resistance of coatings grown in the intermediate pressure regime.
Citation: Materials Science and Engineering A
Pub Type: Journals
electron beam evaporation, scanning electron microscopy (SEM), yttria stabilized zirconia, thermal conductivity, ultrasmall-angle X-ray scattering, directed vapor deposition