Structure and Properties of Multilayer Ti-DLC Films with Ti Element Doping
In harsh marine environments,traditional diamond-like carbon(DLC)films as protective coatings have problems of wear and corrosion failure,which seriously affect the reliability and service life of marine engineering equipment.Ti/TiN/TiCN/Ti-DLC composite films were prepared on 316L stainless steel by medium-frequency magnetron sputtering technology to improve the wear and corrosion resistance of the traditional DLC films.Scanning electron microscopy(SEM),Raman spectroscopy.X-ray photoelectron spectroscopy(XPS)and X-ray diffraction(XRD)were applied to analyze the effects of different Ti doping contents on the structure and morphology of composite films.Furthermore,the effects of different Ti element doping contents on the mechanical properties and wear and corrosion resistance of the composite films were investigated by nanoindentation test,bonding force test,friction and wear test,and electrochemical test.The results indicated that the surface of multilayer Ti-DLC films with different Ti element doping contents was dense and free of obvious defects,but there were cluster particles on the surface of the films.Compared with multilayer pure DLC films,the doping of Ti element reduced the density and size of cluster particles on the surface of the films.With the increase in Ti doping content in DLC film layer,there was an initial rise followed by a subsequent decline in sp3 carbon content within DLC film layer.With the increment of Ti target deposition current,the kinetic energy of sputtered Ti particles gradually intensified,facilitating their effective bombardment on the amorphous carbon-based network structure.Consequently,this promoted easier formation of sp3 carbon by C atoms and led to an increase in the content of sp3 carbon within the film.However,with the further increase of Ti target deposition current,Ti element content in the film gradually increased,resulting in the catalytic effect of Ti element playing a leading role in DLC film and the increase of sp2 carbon content in DLC film layer.The maximum sp3 carbon content in DLC film was observed at Ti element content of 5.10％(atom fraction).The doping of Ti element into DLC film layer could enhance the mechanical properties of the film.With the increase in Ti element doping content,the adhesive force of the film initially increased and then decreased.The adhesive force reaches its maximum value of 27.6 N when Ti content was 6.31％.However,there was little difference in the adhesive force of multilayer Ti-DLC film when Ti content in DLC film was greater than or equal to 5.10％.Moreover,as Ti element doping content increased,both the hardness and elastic modulus of the film exhibited an initial increase followed by a decrease,which was consistent with variations in sp3 carbon content within the film.This suggested that changes in the electronic structure of carbon within Ti-DLC film layer significantly influenced its nano hardness.The friction coefficient of 316L stainless steel was approximately 0.80 under a load of 2 N,while the friction coefficient of multilayer Ti-DLC films,prepared with varying contents of Ti element doping,ranged between 0.2 and 0.4.Notably,the friction coefficient of the prepared multilayer Ti-DLC films was significantly lower than that of 316L stainless steel.This observation highlighted the excellent wear resistance and friction reduction properties exhibited by the multilayer Ti-DLC film,which effectively served as a protective barrier for 316L stainless steel.According to the analysis of electrochemical impedance results,it could be concluded that when Ti element doping content was 5.10％,the corrosion resistance of multilayer Ti-DLC films was the best.This phenomenon might be attributed to changes in the surface DLC film structure caused by variations in sp3 carbon content and the size and quantity of TiC nanophase.The corrosion resistance of DLC films was closely related to sp3 carbon content within the carbon matrix.When sp3 carbon content in the film increased,the electrochemical inertia of the film surface became enhanced,leading to a decelerated electron transmission rate on the film surface and consequently resulting in higher electrochemical impedance.Meanwhile,an increase in sp3 carbon content could also contribute to a denser structure of DLC film.However,when Ti elements were doped into DLC films,TiC particles formed which created pathways for corrosive media to penetrate the film,resulting in decreased corrosion resistance.The synergistic effect between sp3 carbon content and number of TiC particles significantly impacted the structural properties of Ti-DLC films.Excessive doping with Ti led to a gradual decrease in sp3 carbon content and an increase in TiC particles,ultimately deteriorating the film's corrosion resistance.Hence,the wear and corrosion resistance of DLC films could be significantly enhanced through the combination of a multilayer structure design and Ti element doping,thereby improving the long-life service performance of DLC films in marine environments.
traditional diamond-like carbon(DLC)filmelement dopingfriction and wearcorrosion resistance
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