Synthesis and mechanical properties of crystalline carbon nitride superhard coatings

Crystalline β-C₃N₄ was predicted to have mechanical properties similar to those of diamond. Until recently, only amorphous carbon nitride coatings were made in spite of numerous attempts. This lack of success in making crystalline coatings suggests that β-C₃N₄ is metastable. Using TiN as seeding layers and under proper processing conditions, we were able to synthesize fully crystalline carbon nitride composite coatings with hardness in the 45-55 GPa range, which is at the low end of diamond. Suggestions for further improvements and implementation with other deposition techniques will be made.