Mechanical properties of boron-carbon-nitrogen coatings obtained by ion beam assisted evaporation

Boron-carbon-nitride films, including amorphous carbon (a-C), carbon nitride (CN_x) and ternary compounds (BC_xN _y), were deposited on silicon substrates by ion beam assisted deposition (IBAD) techniques. The films were deposited by evaporating either graphite or boron carbide (B₄C) targets, with simultaneous ion bombardment from a precursor N₂+CH₄ +Ar gas mixture. IBAD has permitted to cover a wide range of compositions as a function of deposition parameters. The composition and bonding structure of the films have been carefully studied, including analysis with powerful characterisation techniques such as time of flight elastic recoil detection analysis (TOF-ERDA) and X-ray absorption near-edge spectroscopy (XANES). Depending on the growth conditions, the ternary films can form true ternary compounds of segregated grains of three different phases: tetrahedral BN and C, hexagonal BN and C, and icosahedral B₁₂-structures. Mechanical characterisation of the films has been also performed, including measurements of hardness, elastic modulus, and friction coefficients. The optimal values encountered are hardness of ~35 GPa, and friction coefficients of ~0.05. The deposition parameters have been related to the composition bonding structure, and mechanical properties of the coatings