| Because of the low ionization of traditional dc magnetron sputtering,? m-size particles inclusions of the arc ion plating and low average deposition efficiency of high power pulsed magnetron sputtering,in this work,we independently developed dual-stage pulsed electric field based on the plasma physics principle that the grain boundaries and defects on the target surface will produce micro hot spots under the double effects of strong plasma bombardment and Joule heat,which leads to the plating materials leaved target by thermionic emission.With the help of thermal emission process,the plating material has the characteristics of high yield and high energy,which increased the deposition quantity and ionization rate providing favorable conditions for the rapid and high densification of the coating.The influence mechanism of different electric field volt-ampere characteristics on the deposition properties of plating materials,microstructure and properties of the coating were studied.The volt-ampere characteristics curves of electric field between cathode Al target,Cu target,Ti target and vacuum cavity wall were measured by current control mode under dc electric field environment.It was found that,compared with Al target and Cu target,Ti target was easier to induce micro-arc discharge.The target voltage increased firstly and then decreased with the increase of the target current.The critical target current at the inflection point was about 15 A.Under the condition that the target current was 20 A and the discharge time was 1 hour,when the dc electric field was used,the surface of the titanium target presents obvious stepped and water wavy morphology.With the continuous extension of the discharge time,the temperature of the micro-area of the target surface raised rapidly,and the titanium target surface was seriously damaged by melting.When the monopulse electric field was used,the surface of the titanium target did not show obvious melting damage due to the on-break characteristics of the electric field,and the target surface presents a concave shape with significant edges and corners.When the stepped double-stage pulsed electric field was used,the overall surface of the titanium target was relatively smooth without obvious melting damage,and the overall target surface presented a rounded pit shape with discrete water ripples.Different leave-target modes of the plating materials lead to significant differences in the microscopic morphology of the target surface.When the plating materials missed the target with collision sputtering,there will be residual spalling pits on the target surface.With the enhancement of the collision sputtering processed,the stepped morphology of spalling layer by layer appeared in the crater area of the target surface.When the plating material leaved the target by thermal emission,there would be rounded pits and tiny melting pits left on the target surface,and the discrete distribution of the melting pits forms a shape similar to water ripple.In the dual-stage pulsed electric field environment,when the electric field volt-ampere characteristics between anode and cathode evolved from the positive ohm relation to the anti-ohm relation,the gas discharge state on the target surface changed from the light purple ring glow discharge with low intensity to the bright white circular micro-arc discharge.The preferred orientation of TiN coating changed from(111)to(111)and(220)crystal planes,the surface morphology changed from loose triangular pyramid structure to dense circular cell structure,and the columnar crystal grows more and more dense.The coating has high hardness(25.7 GPa),strong film substrate bonding strength,low friction coefficient(0.55),good wear and corrosion resistance.High density plasma can be produced by the combined action of collision enhanced thermal emission hybrid mechanism,which is helpful to optimize the structure and properties of the coating in essence from the growth kinetics.Under the condition of micro-arc discharge induced by dual-stage pulsed electric field,with the prolongation of deposition time,the residual stress in the coating changed from compressive stress to tensile stress,which was mainly caused by the change of stress dominant mechanism,grain size and deposition temperature.When the deposition time is 80 minutes(the film thickness is 4140 nm),the residual compressive stress of the coating was about-0.54 GPa,and its mechanical,wear resistance,corrosion resistance and other comprehensive service properties were optimized.Under the same target power condition,comparing the microstructure of TiN coatings deposited at different electric fields,it was found that the surface particles of the coatings deposited under the traditional dc electric field are angular and coarse,and the surface of the coatings deposited under high power pulsed electric field was loose cauliflower-like structure and the section columnar crystal was refined.Under the dual-stage pulsed electric field,the surface of TiN coatings deposited showed mutual interaction of large and small particles.These results showed that the doped round-cell structure,columnar crystal in profile was significantly refined,and the atomic accumulation thickening mechanism of deposition crystallization growth was maintained.Under dc arc electric field,there were large melting particles with micron size on the surface,and the profile was very dense.At the same time,comparing the average deposition rate and performance of the coating,it is found that the average deposition rate of the coating prepared under the dual-stage pulsed electric field can reach 51 nm/min.The hardness of the coating deposited under the dual-stage pulsed electric field is 28.5 GPa and the adhesion force of the film substrate is 25.5 N.The dual-stage pulsed electric field can not only effectively increase the deposition quantity and ionization rate,but also effectively improve the microstructure and comprehensive properties of the coating. |
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