Study On Arc Discharge And Macroparticle Defects Of Titanium Target During Cathodic Vacuum Arc System

Tool coating,with high hardness,low friction,high temperature resistance,and toughness,is one of the core cutting technologies for realizing modern manufacturing based on numerical control machine tools.Cathodic arc evaporation?CAE?method has the features in high metal ionization rate,fast deposition rate,and good film-based bonding.Therefore,nitride hard coating prepared by CAE method is a typical coated on cutting tools for processing iron-based materials,lightweight,and difficult-to-machine materials.However,due to the arc generation and irregular movement of arc spot,the co-deposition of macroparticles in the coatings is serious,thus the coating grain is coarse and the quality is poor.As a result the application and development of CAE in cutting tools is severely restricted.In this thesis,arc spot motion behaviors on the surface and near surface of the cathode are established through experimental measurements,geometry and magnetic field modeling analysis.Furthermore,taking the coupling of electromagnetic coils with magnets into consideration,the magnetic induction intensity distributions under different coil currents and the influence on the trajectory of the arc spot are studied.Finally,we systematically studied the effect of arc current and coil current on the surface morphology and macroparticle size distribution in Ti and TiN coatings.The results of this researches provide a theoretical basis and technical guidance for the research and engineering application of controlled cathode technology in the preparation of titanium-based coatings.First,we established the controlled cathodic arc geometrical model.Then a physical model was built by COMSOL to analyze the dependence between the oblique magnetic field and the motion of arc spot.Based on an established Matlab script,distribution,size,motion trajectory and operating speed of arc spots on cathode surface were analyzed under different arc currents,such as 100 A,90 A,80 A,70 A,and 60 A,in Ar and N₂ atmosphere respectively.By the plasma sheath model and the analysis on the movement of charged particles,the relationship between the oblique magnetic field distribution and the arc spot motion trajectory was established.The results showed that in the weak magnetic field on cathode surface,the arc spots moved spiral inward and outward alternatively accompanied by a few random movements.Furthermore,a finite element analysis model on the coupling of the electromagnetic field with permanent magnetic field was built to study the magnetic induction intensity distribution on cathode surface under different coil currents,the influence of the coil current on the trajectory of the arc spot was also investigated.Combining with experimental analysis,it shows that the motion of the arc spot on the cathode surface is mainly affected by the parallel component and the vertical component of the magnetic induction intensity.By adjusting the coil current,different parallel and vertical component distributions can be obtained.The stronger the parallel component of the magnetic induction intensity is,the faster the arc spot rotation rate is;the smaller the parallel component maximum arc spot size is;when the parallel component is zero,the irregular movement is significantly enhanced,and the spot size becomes larger.Meanwhile,the vertical component of magnetic induction intensity also has a great influence on the distribution of the spot.When the intensity difference between the parallel component and the vertical component is small,the arc spot is uniformly distributed on cathode surface,and the spot size is small.When the radial gradient of the vertical component is large,the larger the magnetic field is,the faster the scanning rate is.Thus the arc spot will rotate for a long time at a place where the vertical component is small.Finally,by studying the film surface morphology and large particles prepared with different arc currents and coil currents,it is found that as the arc source current decreases,cathodic arc discharge weakens,and the motion of the arc spot also changes,the roughness of the deposited coatings is reduced.When the coil current of the coupled electromagnetic field is 3.5 A,the difference between the parallel component and the vertical component of the magnetic field is small,large particles on the surface of the film are suppressed.As a result the roughness of the Ti film is 103 nm,and the roughness of the TiN film is 20.2 nm.Compared with the coatings deposited without the electromagnetic field,the roughness is reduced halfly.