Study On The Preparation And Properties Of Hydrogenated Diamond-like Carbon Films For Hydraulic System

The hydraulic system is widely used in the fields of machinery manufacturing,national defense and military,but the stability of the equipment is greatly threatened by the harsh service environment.The wear of the key components is the main problem among the equipment failures.The traditional surface hardening technologies such as chromium plating,nitriding and thermal spraying have limited effect on enhancing the wear resistance of hydraulic components.Due to their excellent wear resistant and antifriction properties,diamond-like carbon?DLC?films are considered as the ideal materials for improving wear resistance of machine parts.In this work,diamond-like carbon thin films were prepared on GCr15 surface by a hybrid physical vapor deposition system based on the medium frequency sputtering and linear ion source.The effects of different transition layer structures,substrate bias and ion source deposition power on the structure and properties of DLC films are investigated systematically.Key points and results are listed as follows:?1?The DLC films with Cr transition layer structure have the best comprehensive performance compared to Cr/CrN transition layer or without transition layer.The hardness and elastic modulus of DLC films are 18.88 GPa and 241.83 GPa respectively.The adhesion strength of DLC film is up to 20 N.During the wear test,the friction coefficient of film is only 0.17 with GCr15 friction pair under the load of7 N,and the wear rate is 4.01×10^-11mm³/N·m.?2?The substrate bias has an important effect on the film surface roughness.The best adhesion strength of 28.6 N is obtained at the substrate bias of-700 V.With the increase of substrate bias?-100^-700 V?,the relative content of sp³ bond in DLC film increases first and then decreases,reaching the maximum value at-500 V.The wear rate of thin film deposited at-300 V is the lowest,about 3.71×10^-11 mm³/N·m.?3?The microstructure of DLC thin film is greatly influenced by the deposition power of linear ion source.With the increase of ion source power,the deposition efficiency increases,whereas the relative content of sp³ bond decreases.The high power of the ion source?1.6 kW?causes the degradation of DLC film.The friction coefficient increases to 0.21 under 7 N loading at 1.6 kW power,and the wear rate rises to 7.78×10^-11 mm³/N·m.The purpose of this work is to develop the DLC film used in hydraulic components with excellent wear resistance property.By optimizing the deposition parameters,high quality Cr/DLC films are prepared on the surface of hydraulic directional control valve.The results in bench test show that wear resistant and antifriction performances of the hydraulic directional control valve are significantly improved,and the service life is prolonged by more than 3 times.