Low-Friction Coatings of Zinc Oxide Synthesized by Optimization of Crystal Preferred Orientation

The crystal preferred orientation of zinc oxide (ZnO) coatings on stainless steel substrates was precisely controlled by a combinatorial sputter-coating system. ZnO coatings were analyzed by X-ray diffraction spectroscopy, and surface and interfacial cutting analysis methods. The frictional properties of the coatings in a vacuum, the atmosphere, oil of n-hexadecane, and oil doped with palmitic acid molecules were observed. Different frictional behaviors of the ZnO coatings were observed by varying the crystal preferred orientation. A low-friction coefficient as less as 0.2 was realized by ZnO coatings with uni- and multi-crystal orientation in all of those conditions. Inverse proportion of the friction coefficient to normal load was observed on ZnO coatings with bi-orientation of (002) and (103) in pure and palmitic acid doped oil.