Functionally graded, nanocrystalline, multiphase, B- and C-based superhard coatings

Candidate ceramic coatings for bearing applications must meet several criteria, such as hardness, to limit abrasive damage. Adhesion is essential to prevent destructive three-body wear. Toughness helps avoid brittle fracture and coating failure. Finally, temperatures during deposition must not damage the substrate. We report fabrication and testing of functionally-graded, nanocrystalline, multiphase Ti/BN coatings by ion beam assisted deposition (IBAD), with these properties. Hardness was measured $>$ 42 GPa. Structural grading transitions from metallic to covalent bonding through the film, controlling constituents (TiN, TiB$_{2}$, B$_{4}$C, BN) to optimize adhesion, internal stress, hardness, and wear resistance. Pin-on-disk wear testing for 5 million cycles at 1 GPa contact stress, showed no wear, to potentially extend lifetimes by orders of magnitude in industrial or biomedical applications.