Preparation And Mechanical Properties Of Selective Bonding Metal Element Doped Diamond-like Carbon Films

Diamond-like carbon（DLC）films have attracted wide attention due to its high hardness,good chemical stability,and low coefficient of friction.However,due to the limitations of the preparation technology,some defects such as high internal stress and low toughness,which restricts its practical development.For the purpose of reducing the internal stress and improving the toughness of the films,we focus on the selective metal element doped DLC films technology.In this paper,the single element Ti-doped（Ti-DLC）and Al-doped（Al-DLC）composite films were prepared by cathode arc deposition technology.The effects of different selectively bonding metallic elements on the microstructure and mechanical properties of DLC films were analyzed in detail.Based on this study,two elements N-Ti co-doped（N,Ti）-DLC and N-Al co-doped（N,Al）-DLC composite films were prepared,and different preparation processes and parameters were explored with two element co-doped DLC composite films.The effects of different preparation processes and parameters on the microstructure,composition,surface morphology and mechanical properties of the dual-element co-doped DLC composite films were explored.The best process conditions were obtained on the basis of this study.The results were shown as follows:（1）Pure DLC film and Ti-DLC and Al-DLC composite films were prepared on single crystal silicon（100）substrates by cathodic arc deposition.Compared with the pure DLC film,it is found that the metal elements incorporated in the films affected the microstructure,surface morphology and mechanical properties of the film.The incorporation of Ti and Al elements in the films promoted the growth of C-sp² hybrid bond clusters.The internal stress of the film was effectively released,the surface roughness increased,and the hardness of the film decreased.However,the hardness of the Al-DLC composite film is lower than that of Ti-DLC composite film.（2）Using ion source assisted cathodic arc deposition technique,six sets of（N,Ti）-DLC composite films under different process conditions were prepared on single silicon（100）substrates.The effects of nitrogen addition（atomic nitrogen N₂,ionized nitrogen N⁺）,DC cathode target current,and pulsed cathode arc discharge frequency on the microstructure,composition,surface morphology,hardness and internal stress of DLC composite films were studied in detail.The choice of nitrogen ion（N⁺）incorporation promoted N bonding with C-sp³ hybrid bond,and the prepared film showed lower surface roughness and finer particle size.The pulse frequency and target current would change the excited plasma energy density.When the C plasma（lower pulse frequency）and Ti plasma（smaller target current）had higher energy density,the C-sp²hybridized clusters of the prepared films was larger and more ordered.With the increase of the pulse frequency and the target current,the stress in the film first increased and then decreased.When the pulse frequency and the target current were（10 Hz,80 A）,The internal stress of the film prepared by atomic nitrogen（N₂）was minimum about 0.6GPa.（3）Using ion source assisted cathode arc deposition technique,five sets of（N,Al）-DLC composite films with different process parameters were deposited on single silicon（100）substrates.The composite films were prepared by ion nitrogen（N⁺）as the N elememnt incorporattion.The microstructure and composition of the（N,Al）-DLC composite films could be regulated by changing the DC cathode target current and pulsed cathode arc discharge frequency,which could optimize the mechanical properties of the film.When the pulse frequency and target current were（3 Hz,80 A）,the content of Al toughening phase in the film was the highest,the scratch crack propagation resistance（CPRs）and plasticity index（H³/E²）were the highest,and the film showed high toughness.