Study Of Bias Voltage Controlled Cage Type Hollow Cathode Discharge Characteristics And Structure And Properties Of Thick Si-DLC Films

Diamond-like Carbon?DLC?film is widely used due to its low friction coefficient,high wear resistance and excellent corrosion resistance.With the progress of modern industry,more attention has been paid to the industry of thick layer DLC film,owing to the higher need of wear resistance and corrosion resistance.Cage type hollow cathode discharge technology with high deposition rate induced by high plasma density is an effective method for fabrication of thick DLC film in numerous preparation methods.However,cage type hollow cathode discharge is featured by the fact that the potential difference between the sample and the plasma is only a few eV,consequently limits the optimization of structure and mechanical properties of DLC film.In this work,a new type bias voltage controlled cage type hollow cathode discharge technology has been proposed,and then its discharge characteristics were studied.Thick multilayer Si-DLC films?>30?m?with high adhesion and deposition rate were successfully prepared.A set of dc bias voltage power supply is applied between the sample and the cage at bias voltage controlled cage type hollow cathode system.This setup allows an independent control of the ion density and the ion energy delivering to the growing film.Breakdown voltage under argon atmosphere is lower than that under acetylene at cage type hollow cathode discharge.This voltage decreases with the increase of working pressure,pulse frequency or pulse width.Cage type hollow cathode discharge is composed of pre-discharge and hollow cathode discharges stages.There is a current decline in initial stage of discharge.It is attributed to the fact that the contaminants and convex structure on the surface are reduced after argon ion etching and then this leads to the decrease of emitted electron number.The effect of working pressure on the discharge intensity under argon or acetylene is different.With the increase of argon pressure,ionization is enhanced and cage current increases.In acetylene cage discharge process,a number of electrons are easy to combine with acetylene molecular,which promotes the formation of negative ions.Consequently the cage hollow cathode discharge is reduced.In argon discharge process,the currents through cage and sample decrease firstly and then increase with the addition of bias voltage.The current reduction is due to the clamping consumption of space carrier and weakness of the cage hollow cathode effect.With the increase of additional bias voltage,sample glow discharge is enhanced.In discharge process with mixed gas of argon and acetylene,the decomposition and ionization of acetylene gas are promoted by mixed argon and cage current increase.Argon discharge plasma mainly consists of activation state of Ar* and Ar⁺ ion.Atomic state H and a small amount of CH,C2 and C ⁺ ion are detected in acetylene discharge process.Ar⁺ ion motion model is established to explain the change mechanism of cage current and sample current.By the etching of Ar ⁺ and H ⁺ ions,carbon contaminations are removed and nanosize?20nm-50nm?bugles are formed on the 316 stainless steel surface,which strengthens the mechanical lock effect and improves the adhesion of Si-DLC film.At the same time,nitride particles and oxygen element are removed effectively by the etching of Ar ⁺ and H ⁺ ions and further improves the adhesion of Si-DLC film.Si-DLC films deposited by bias voltage controlled cage type hollow cathode discharge prossesses a lower surface roughness and more dense structure.The deposition rate of Si-DLC film decreases firstly and then increases with the rise of the additional bias voltage.The reason for the reduction is the chemical etching of hydrogen atom and sputtering of Ar⁺ ion.Along with the increase of additional bias voltage,the decomposition of acetylene gas is enhanced and the deposition is increased.The dense structure and reduction of H contents by the ion bombardment are the main reasons for the improvement of mechanical properties of Si-DLC films.The hardness of Si-DLC films is enhanced from 8GPa to 14 GPa and the Si-DLC film deposited with-300 V additional bias voltage shows better wear-resistance properties.Compared with the Si-DLC film deposited by conventional cage type hollow cathode discharge technology,Si-DLC film with soft and hard alternate structure possesses higher adhesion and toughness.The scratch binding force(L_C2 value)of Si-DLC film deposited on 316 stainless steel substrate increases from 17 N to 30 N.At the same time,using the bias voltage controlled cage hollow cathode system,together with duplex treatment of plasma nitriding of 316 stainless steel and consecutive deposition of Si-DLC film,the L_C2 value reaches 46 N.Scratches toughness test of Si-DLC multilayer films deposited on HSS steel substrate shows that the scratch toughness value increases with the increas e of film thickness,and reaches to 2695 at the thickness of 35?m.The L_C2 value also increases to 112 N.Friction and wear experiments show that the thick Si-DLC film has lower friction coefficient and excellent wear resistance against GCr15 or Si C balls.The thermal stability of multilayer thick Si-DLC films is superior to those deposited by conventional technology.Bias voltage control and multilayer structure design increase the film density and reduce the pinhole defects in multilayer Si-DLC films.This leades to excellent erosion resistance in 15%HCl solution.Si-DLC film of 152?m thickness can be successfully deposited on silicon wafer by the new type bias voltage controlled technology.