Superhard CrN/MoN films with multilayer architecture

The main regularities of the formation of microstructure and properties of multilayer nanostructured CrN/MoN films with periodically changing architecture of layers were considered. The transition metal nitride coatings with high hardness and wear resistance were obtained by vacuum-arc evaporation of the cathodes (Arc-PVD) in nitrogen atmosphere at several sets of predetermined deposition parameters. CrN/MoN multilayers were fabricated using constant nitrogen pressure of 0.4, 0.09 and 0.03 Pa. All samples were divided into three main series depending on the values of bias voltage applied to the substrates (-20, -150 and -300 V). Each serial of samples contain multilayer films varying in the individual layer deposition time and, hence, thickness, which is in range from 1.7 μm to 20 nm. The morphology of surface and microstructure of cross-sections were studied by scanning electron microscopy (SEM). Elemental composition and elemental depth profiles were characterised by energy-dispersive X-ray spectroscopy (EDS), secondary-ion mass spectrometry (SIMS), Rutherford backscattering spectrometry (RBS) and high-resolution transmission electron microscopy (HRTEM) EDS. Microand nanostructural analysis of the films was performed by X-ray diffractometry (XRD), grazing incidence XRD (GIXRD), in-plane XRD, electron backscatter diffraction (EBSD) and HRTEM selected area electron diffraction (SAED). The main phases formed in films were two CrN and γ-Mo2N nitride phases with cubic lattice of NaCl type and not significant volume of additional metastable MoN cubic phase depending on nitrogen pressure and bias voltage. The preferential orientation of planes changes from [311] to [111] and [200] with the increase of absolute value of bias voltage from -20 V to -150 V and -300 V respectively. The size of nanograins in coatings with a nanometre bilayers thickness was about 12 nm, while micro-deformation of nanocrystallites was about 0.5-0.6%. Coatings with thin nanoscale bilayers have shown high hardness (38-42 GPa) and strong wear resistance, which makes them appropriate and promising for industrial applications as protective ones. The relations between deposition conditions and obtained composition, structure and features were studied. The best parameters and deposition conditions were discussed as recommended to achieve superior mechanical and physical properties of coatings with long lifetime and applicable for harsh environment.