| For the technical shortcomings that the low ionization rate of deposited particle in magnetron sputtering possess and the high-temperature molten drop easily mixed into the deposited particle in cathodic-arc ion plating,based on phycical theory that the bombardment region of Ar+ on the target surface can be limited by cathodic magnetic field and evolved electron rate at defects?such as the grain boundary?in target surface is about 30 % of the intracrystalline when the target surface was bombarded with the same intensity of Ar+,meanwhile Joule's effect?Q=I2Rt?can be produced to aggravate the disproportionate distribution of evolved electron rate,we in this work,regulated the incremental step target current between inagnetron cathode and vacuum chamber and different pulse characteristics which induced micro-arc discharge on target surface and deposited particles escaped target surface,through collision induced heat emission.The influence of three discharge regions?glow,micro-arc and arc?with different volt-ampere characteristics on escape-target mode of deposited particles was studied,and the mechanism of escape-target mode on microstructure,mechanical and tribological properties of coatings was also analyzed.The main results as follows.During measuring the volt-ampere characteristic curve of gas discharge between the cathodic Ti target and the anodic chamber,it was found that micro-arc discharge on the target surface would be introduced at a critical target current density,which was larger than 0.175 A/cm2 in the dc incremental step electric field.After inducing micro-arc discharge,the target surface was presented a discrete ditch shape.It was different from the irregular concave shape of escape-target with collision and small round pit shape of escape-target with heat emission.The escape-target mode of deposited particles on defective regions transferred from collision to heat emission when the micro-arc discharge was introduced onto defects of target surface.The pure Ti coatings were deposited at micro-arc discharge region with a current density of 0.267 A/cm2.The reduction rate of the thickness was 72.1 %,and the coating presented dense columnar structure.Meanwhile,there was no any big micron-sized particle on its surface.The adhesion of coating deposited at micro-arc discharge region was 34 N.The dc incremental step electric field could induce the micro-arc discharge on the target surface.But in slightly longer duration the micro-region would be melted since its temperature reached or exceeded the melting point of target materials,which affected the application of film process.By independently controlling Ton and Toff of the target peak current in pulsed electric field,it not only achieved micro-arc discharge on target surface,but also avoided the melting of micro-region due to accumulation of thermal energy.The critical current density was 0.225 A/cm2 when the gas discharge transformed from glow region to micro-arc region in pulsed mode(Ton=24.5 ?s,Toff=0.5 ?s).Temperature rise on target surface was viewed as a prerequisite about inducing and keeping the condition of micro-arc discharge,the pulsed electric field slowed the stronger effect of temperature rise on target surface than that of dc electric field.So it would need a larger target current density so that the micro-arc discharge was induced in pulsed electric field.At the moment,the averaged deposition rates of pure Ti coatings were 141 and 132 nm/min respectively at current density of 0.310 and 0.357 A/cm2,and possessed dense columnar structure.The thickness reduction rate along the direction of target-substrate distance decreased from 84 to 80 % with the current density increasing from 0.310 to 0.357 A/cm2.The adhesion increased from 15.3 to 25.2 N.It showed that the thickness was uniform along the direction of target-substrate distance,and the adhesion was improved in micro-arc discharge region at the higher peak target current density.According to the principle of equal-flux of pulsed electric field,the peak target current density could be obtained several times higher than that in the dc electric field under the same conditions of average power.It would facilely induce and keep the conditions of micro-arc discharge on the cathodic target surface.Also in this paper,a design concept of target peak current presenting “step” in one Ton period was put forward,which could satisfy the demand that the high peak current realized quick escape-target of deposited particles and achieved the high average-deposition rate of coating by increasing the pulsed width.When the pure Ti coatings were deposited using different electric fields,the dual power pulse?DPP?had much more dense microstructure and the critical load was 12.0 N.Moreover,the average-deposition rate of coating deposited via DPP was 80 nm/min and the real-time deposition rate was 132 nm/min.Meanwhile,the pure Ti coatings were deposited at micro-arc discharge region with different peak current densities using DPP electric field.It was found that the average grain size of coatings decreased from 18 to 10 nm,the hardness increased from 1.2 to 5.6 GPa with the current density increasing from 0.27 to 1.35 A/cm2.The increase of peak current density at micro-arc discharge region could decrease the grain size of coatings and refine the size of grain.TiN coatings were deposited at a peak current density of 0.87 A/cm2 using DPP,it was found that the DPP TiN coatings represented the grain size of 12 nm,the hardness of 29.6 GPa,the modulus of 377.1 GPa and the corrosion rate of 5.5×10-5 mm/a.It could provide the some references for TiN coating deposition. |
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