Deposition and characterization of superhard biphasic ruthenium borides films

Recently, the superhardness of rhenium diboride films was reported. In this study the first successful preparation and characterization of ruthenium boride films is presented. The morphology, topography, microstructure and hardness of films, prepared by pulsed laser deposition, were investigated. The films, which are 0.7 μm thick, have a dense grain texture, and are composed of two phases Ru2B3 (main phase, 65% volume fraction) and RuB2 (35%). The RuB2 phase does not show any preferred orientation, while Ru2B3 is textured preferentially along the (1 1 4) and (1 0 5) directions, with crystallite growth parallel within 1.9° of average mismatch. The composite Vickers microhardness of the film–substrate systems was measured, and the intrinsic hardness of the films was separated using an area law-of-mixtures approach. The obtained films were found to be superhard, the intrinsic film hardness value (49 GPa) being much higher than that for the RuB2 bulk used as the target for film deposition and than that for the Ru2B3 bulk