Research On Low Voltage Deposition Of Diamond-like Carbon Film On Stainless Steel Surface

Stainless steel is one of the most widely used structural materials in industry today,but it is inevitably affected by corrosion and wear in many environments due to its components.DLC films can be used in a wide range of applications（chemical,optical,electrical,tribological,etc.）because they combine the properties of diamond and graphite.Here are many ways to prepare DLC films,and electrochemical deposition technology has attracted a lot of attention because of its simple equipment,convenient operation and scaleable production.Electrochemical deposition of DLC films still has shortcomings,such as high deposition voltage and slow film formation rate in organic solvent systems.The problems of hydrogen precipitation and side reactions of alcohols in aqueous systems have greatly limited the research on DLC films.In this study,DLC films were deposited on stainless steel surfaces at low potentials using formic acid as the carbon source in an aqueous solution,however the current efficiency was too low.The current efficiency and deposition rate were improved by adding sodium formate to increase the p H and reduce the hydrogen precipitation side reaction.To further improve the deposition efficiency,DLC films were prepared using a solvent mixture of dimethyl sulfoxide（DMSO）and water,with formic acid as the carbon source.DMSO can bind the H in H₂O through the DMSO-H₂O intermolecular hydrogen bonding network,thereby reducing the water activity and thereby inhibiting the hydrogen precipitation reaction.The effects of electrolyte and deposition conditions on the structure,surface morphology,corrosion resistance and friction resistance of the carbon films were investigated as follows.1.Study on electrochemically deposited diamond-like films in aqueous solutions of formateDLC films were electrochemically deposited at a lower potential（-4.0V vs.Ag/Ag Cl）using aqueous formic acid solution as the electrolyte.The effects of carbon source concentration in aqueous formic acid solution with different concentrations on the structure,morphology and thickness of DLC films as well as the current efficiency of electrochemically deposited DLC films were investigated.The by-products generated during the deposition process and the reduction behaviour of formic acid were also investigated.Formic acid molecules and formate ions were simultaneously reduced to DLC films,and the current efficiency increased as the thickness of the films became thicker with increasing reactant concentrations.Raman spectroscopy showed that the DLC films were deposited on stainless steel.2.Electrochemical deposition of diamond-like films in aqueous solutions of formic acid and sodium formateIn this part,DLC films were electrochemically deposited using different ratios of formic acid and sodium formate as electrolyte to investigate the effect of electrolyte p H on the morphology and thickness of DLC films,and to investigate the deposition rate during the deposition process,and to select the optimum ratio of formic acid to sodium formate according to the deposition rate.In the optimum ratio of formic acid to sodium formate solution,the optimum deposition potential is selected based on the current efficiency.The effect of the thickness of the DLC film on the corrosion resistance and friction resistance of the film was investigated in the optimum electrolyte and at the optimum potential.The deposition rate of the prepared DLC films was significantly increased by the addition of sodium formate.The maximum deposition rate and current efficiency were achieved at a deposition potential of-3.0 V（vs.Ag/Ag Cl）in 4 mol·L^-1 formic acid and 1 mol·L^-1 sodium formate electrolytes.The FTIR spectra show that the prepared films are hydrogen-containing DLC films.The greater the thickness of the film,the greater the corrosion and friction resistance.3.Electrochemical deposition of diamond-like films in aqueous formic acid and DMSOIn order to broaden the electrochemical window of the solvent and reduce the cathodic hydrogen precipitation reaction,a mixture of water and dimethyl sulfoxide（DMSO）was used.The DLC films were electrochemically deposited in 5 mol·L^-1 formic acid and 0.25 mol·L^-1sodium formate（DMSO-H2O（1:1））solutions to investigate the current efficiency at different tank voltages and to investigate the effects of different tank voltages on the structure,morphology,thickness,corrosion resistance and friction resistance of the DLC films.The addition of dimethylsulfoxide inhibited hydrogen precipitation and significantly improved the current efficiency of the DLC films compared to the electrolyte without DMSO.SEM showed that as the deposition voltage increased,dense films were formed on the cathode surface,the thickness of the DLC films tended to increase and then decrease,and the average grain size and sp³ heterogeneous carbon content of the films increased.