Synthesis of Coatings With Hardness Exceeding 40 GPa by Magnetron Sputtering

Abstract

Single- and dual-cathode DC magnetron sputtering was used to produce TiB2 coatings and CNx/ZrN multilayers, respectively, with hardness exceeding 40 GPa. The composition, structure, topography, and mechanical properties were determined by various techniques, including Auger electron spectroscopy, X-ray diffraction, high-resolution electron microscopy, atomic force microscopy, and nanoindentation. An optimum combination of the sputtering pressure and substrate bias results in the production of ultrasmooth TiB2 coatings with hardness up to 50 GPa and excellent wetting properties. The rationale for studying the CNx/ZrN system is that ZrN(111) provides excellent lattice match to the hypothetical β-C3N4(0001) face (β-C3N4 was predicted to have mechanical properties comparable to diamond). Using a dual-cathode sputtering system, we produced crystalline multilayers of CNx/ZrN with bilayer thickness of 1–2 nm. Using various combinations of nitrogen partial pressure, target powers, and substrate bias, we found that the hardness of these coatings correlates very strongly with the occurrence of (111) texture of ZrN, consistent with the lattice-match strategy. Even with a ZrN volume fraction of 70 percent, such multilayer coatings have been synthesized with hardness in the 50 GPa regime.