SPUTTER-DEPOSITED ZIRCONIA-ALUMINA NANOLAMINATE COATINGS

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