Study On The Structure And Properties Of WC/aC:H Film And Tribological Behavior In Water-based Environment

Diamond-like carbon film?DLC?have been studied for more than sixty years,but they are still concerned by their excellent tribological properties and chemical inertness.It was found that the tungsten doping can control the way of interdigitation of the carbon-based network in the film and change the proportion of sp2 and sp3 hybridization,which can effectively improve the overall performance of the film and enhance the adaptability of the film in harsh environments.However,the research and reports of WC/DLC films in the water-based environment are relatively lacking,especially the mechanism of friction and failure in the water-based environment has not been clearly described.In this paper,a series of WC/a-C:H films were prepared by unbalanced magnetron sputtering and plasma-enhanced vapor deposition.The X-ray diffraction?XRD?,Raman spectroscopy,scanning electron microscopy?SEM?,and X-ray.Photoelectron spectroscopy?XPS?,transmission electron microscopy?TEM?,nanoindentation instrument,scratch tester,and friction tester were used to characterize the structure and properties of the WC/a-C:H films.Experimental results are as follows:The as-deposited WC/a-C:H film has a columnar crystal compact structure containing?-WC_1-x nanocrystals and amorphous carbon matrix.As the sputtering target current rises,the series of the WC/a-C:H film has the higher film-bonding strength,lower hardness and lower elastic modulus,which is mainly due to the high sp2 content in WC/a-C:H film.With the increase of sputtering target current,four multilayer films exhibited good wear resistance.The friction coefficient and wear rate increased first and then decreased.At a sputtering target power of 1.4kW,a dense structured and high-performacne WC/a-C:H film?S2?is obtained.The hardness and elastic modulus are 13 GPa and 173 GPa,respectively.The coefficient of friction was 0.15,and the wear rate was 3.92×10-7mm3/Nm.The failure mechanism of the interface under three failure modes are studied.It is found that the film and the substrate are both in elastic deformation,the tribological load-bearing capacity of the WC/a-C:H film is proportional to the mismatch strain of the interface.The magnitude of the mismatch strain energy in the ideal state can be quantified by the mismatch.316 stainless steel own the highest tribological load-bearing capacity among all samples.The main friction process in the different environments was mechanical wear,and changes in the lubrication conditions and the occurrence of friction chemical reactions only partially changed the friction properties of the film.The match of the surface and mechanical properties of the WC/a-C:H film with those of the friction counterpart was a key factor in determining the service life of the WC/a-C:H film and the optimum lubrication process.In emulsions containing different volumes of base oil,changes in the viscosity of the emulsion can affect the removal of wear debris and cause the destruction of the transfer film.The appropriate concentration ratio can lubricate the surface of WC/a-C:H film and promote the graphitization of the friction surface.Proper bias voltage optimization can be applied to WC/a-C:H films consisting of ultrafine nanocrystalline and a large number of SRO clusters.This new nano-material exhibits superior mechanical and tribological properties.The right amount of defects can store debris and particles to help slow erosion by seawater and can help to quickly form a transfer film.The M2 film had the best COF?0.12?and wear rate?6.2×10-8mm3/Nm?among the films fabricated.