Microstructure and mechanical properties of atomic layer deposited alumina doped zirconia

Atomic layer deposited alumina doped zirconia films can exhibit advanced mechanical properties with potential to increase the suitability of ZrO2 films for mechanically resilient coatings. In the present study, Al2O3-doped ZrO2 films were deposited on a TiN substrate to thicknesses around 100 nm at 300 °C. A zirconia film containing 4.6 mol. % Al2O3 was crystallized in its tetragonal polymorph. Increasing the Al2O3 content up to 5.8 and 8.2 mol. % stabilized the cubic polymorph in the ZrO2-based films. The films with even higher Al2O3 contents remained amorphous. All the crystalline films possessed a preferential grain orientation to extents differing beneath the surface and in the vicinity of the substrate. The most rigid films with hardness up to 15 GPa and elastic modulus above 170 GPa could be obtained when crystallized in the form of cubic ZrO2 stabilized upon doping with Al2O3. For all the crystalline films, the hardness and elastic modulus increased near the substrate.