Nanostructured ceramic coatings: zirconia single layers and nanolaminates

摘要

Controlled scaling of structure at the nanometer level can produce ceramics with unique phase constituency and properties. As a demonstation, we use the example of retained tetragonal zirconia production in sputter deposited single layer and zirconia-alumina nanolaminate coatings. We present a map showing the kinetic limits (deposition rate, temperature) of tetragonal zirconia formation in single layer coatings. Based on the hypothesis that tetragonal zirconia exists in crystallites that are below a critical size, r_C (backed by end-point thermodynamics calculations), we employ a zirconia-alumina nanolaminate structure to limit zirconia crystallite growth. We show that if the zirconia layer thickness in the nanolaminate is less than r_c, the tetragonal phase is produced solely, independent of the kinetic parameters that control its production in single layer zirconia films, and without the addition of a stabilizing dopant.