SPUTTER-DEPOSITED ZIRCONIA-ALUMINA NANOLAMINATE COATINGS

The mechanical properties of zirconia are known to be a function of phase composition. This article shows that a nanolaminate geometry can be used to control the phase composition of zirconia thin-film coatings. The nanolaminates consist of nanoscale multilayers of polycrystalline zirconia and amorphous alumina grown by reactive sputter deposition. X-ray diffraction and high-resolution electron microscopy results show that both monoclinic (m) and tetragonal (t) zirconia polymorphs are formed in the zirconia layers. The zirconia layers have a strong crystallographic texture. Most zirconia crystallites grow with closest-packed planes (either t{111} or m{11 ($) over bar 1}) oriented parallel to the substrate. The volume fraction of tetragonal zirconia, the desired phase for transformation-roughening behavior, increases with decreasing zirconia layer thickness. Nanolaminates with a volume fraction of tetragonal zirconia exceeding 0.8 were produced without the addition of a stabilizing dopant, and independent of the kinetic factors that limit tetragonal zirconia growth in pure zirconia coatings.