Characterization Of Diamond-like Carbon Films Deposited On Inner Surface Of Stainless Steel Tubes

Diamond-like carbon film has lots of excellent properties,such as high hardness,high wear resistance,low friction coefficient,good chemical inertness,which makes it have great prospect in the field of inner surface of metal tubes.However,it remains a challenge when the inner surface of tubes with large length-diameter aspect ratio is involved.The difficulty lies in that how to generate plasma inside of the tubes and in that how to achieve inner surface modification of tubes.Our laboratory has developed a normal DC glow discharge method for the inner surface modification of stainless steel tubes with inner diameter of 10mm.In this work,we present our study on techniques parameter for DLC deposition and properties of DLC films deposited on inner surface of 304 stainless steel tubes with inner diameter of 10mm.The influences of deposited time,gas flux and the ratio of working gas on film's structure and properties were discussed.The microstructure and morphology of the films were studied with Raman spectroscopy,FTIR spectroscopy,scanning electronic microscopy(SEM) and AFM.The mechanical and tribological properties were tested by microhardness tester and friction and wear tester.The corrosion-resistance was tested by electrochemical measurements. The main research works and results are as follows:DLC films about 1.5μm thick was deposited on the 304 stainless steel substrate by the method of DC glow plasma CVD.The films are soft and have relatively loose adhesion with substrate.Island particles can be observed on the surface of films.The sp³/sp² ratio of the films increases as the increment of deposited time and raises first then drops as the increment of gas flux,and decreases as the increment of concentration of CH₄.The hardness of film can reach up to 10 GPa at 30 min deposited time,26 SCCM gas flux,20%concentration of CH₄. With an increase of deposited time,the behavior of corrosion-resistance is better.Too low gas flux and too high concentration of CH₄ both take influence on the corrosion-resistance of the DLC film coated inner surface of 304 stainless steel tube.Especially,DLC film can drastically improve the corrosion-resistance of inner surface of 304 stainless steel tube in the case of 42 SCCM gas flux,20%concentration of CH₄.