Preparation and Characterization of Superhard Materials of Crystalline Carbon Nitride

13. ABSTRACT (Maximum 200 words) Prompted by the prediction of Cohen and coworkers that beta carbon nitride may have properties similar to diamond, there have been many attempts to synthesize this hypothetical metastable material. We successfully synthesized this material via epitaxial stabilization using TiN(lll) and ZrN(lll) as the growth template. The coatings were CN/TiN or CN/ZrN multilayers grown in a dual-magnetron system. The existence of beta carbon nitride in these multilayers has been confirmed with cross-section electron diffraction, Rutherford backscattering, Raman spectroscopy and near-edge x-ray diffraction. Most important, these multilayers exhibit hardness in the 50 GPa, in spite of the large volume fraction (60-70%) of the softer TiN or ZrN component. Attempts to improve the hardness by using TiB2 (which is harder than TiN and ZrN) as the growth template did not work as well because TiB2 was markedly softened by the presence of nitrogen. Nevertheless, carbon nitride/TiB2 multilayers achieved hardness in the 30-40 GPa range. Lubricated tribo-testing indicated that these very hard coatings exhibit wear coefficients ten times better than conventional TiN coatings. This work was extended to include BNxCy by magnetron sputtering of B4C in a mixed argon/nitrogen ambient. Depending on the process conditions, one can obtain a mixture of h-BN+amorphous carbon nitride to c-BN with excellent electrical and tribological properties.