Structure and properties of multi-component and multilayer TiCrBN/WSe x coatings deposited by sputtering of TiCrB and WSe 2 targets

Abstract

Single-layer (SL), double-layer and multilayer (ML) TiCrBN/WSe x coatings were deposited by sputtering of TiCrB and WSe 2 targets in a gaseous mixture of argon and nitrogen. To enhance film adhesion, ion implantation was employed at the initial stage of deposition for 5 min. The structure and chemical composition of the coatings were studied by means of X-ray diffraction, scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The coatings were characterized in terms of their adhesion, hardness, elastic modulus, elastic recovery, internal stress, corrosion resistance, friction and wear. All coatings showed a dense structure free of columnar grains. The ML TiCrBN/WSe x coating demonstrated a sequence of nanocrystalline TiCrBN and amorphous WSe x layers with various thicknesses. The SL TiCrBN/WSe x coating deposited at magnetron current of 2 A displayed completely amorphous structure. As the magnetron current was decreased to 1 A, the coating consisted of mixture of face centred cubic (Ti,Cr)(B,N), WSe 2, and amorphous a-phases. This multi-component TiCrBN/WSe x coating showed almost the same hardness of 30 GPa as the SL TiCrBN coating. The incorporation of WSe x into TiCrBN coating was shown to decrease the friction coefficient in air from 0.5 to 0.2–0.25 with only little influence on the wear resistance and electrochemical behavior. In the case of SL TiCrBN/WSe x coatings, the friction curves were typically flat with a very short running-in stage which did not exceed 50 m, whereas in the case of ML TiCrBN/WSe x coating, the fluctuations and spikes of friction coefficient were observed. It has been confirmed by Raman spectroscopy that the existence of WSe 2 phase in sliding contact during the tribological test provides low friction. To evaluate thermal stability, the SL TiCrBN/WSe x coating deposited at magnetron current of 1 A was annealed in vacuum at 550 °C for 1 hour. The superior tribological performance of the SL TiCrBN/WSe x coating after annealing can be explained by the presence of two constituents, of which one is a hard and oxidation resistant (Ti,Cr)(B,N) phase with a grain size of a few nanometers and the other is a mixture of WSe 2 + a-WSe x solid lubricant grains and/or inter-granular phases.