The High Performance Of Anticorrosion And Wear Resistance Films Deposited On Medical Stainless Steel

Surface modification is an important means to improve the performance of medical stainless steel,and the surface modification of diamond-like carbon film(DLC)can provide good wear resistance,corrosion resistance and biocompatibility.However,DLC film will fail prematurely due to corrosion and other problems during long-term use.There are currently few studies on the in vivo failure of DLC films.The mainstream view is that DLC films has crevice corrosion in the human body,causing the film to peel off.The corrosion rate of the film increases sharply during crevice corrosion.Corrosion spreads to the film laterally,causing the film to peel off before reaching the design life,and lose the protection of the material.Therefore,exploring the specific corrosion failure behavior of DLC film in the human body fluid environment is of great significance to the long-term use of DLC film in the human body.In this paper,plasma-enhanced chemical vapor deposition technology was used to prepare DLC films on 304 stainless steel,high nitrogen nickel-free stainless steel and 316L stainless steel under different pulses,different pulse widths and different tetramethylsilane gas flow rates.The composition and surface morphology of DLC films were characterized by Raman,infrared spectroscopy and atomic force microscope.The mechanical properties of DLC films were characterized by nanoindenter,step tester,scratch tester and super depth-of-field microscope.The electrochemical work station,wear corrosion device and crevice corrosion device were used to characterize the electrochemical performance of DLC film,and the film forming mechanism of DLC film was discussed,and the influence of composition structure on mechanical and electrochemical performance was analyzed.The local corrosion mechanism of DLC film is studied and the wear corrosion and corrosion behavior are analyzed.The main progress made in the thesis is as follows:The effect of pulsed negative bias on the composition and structure of DLC films was studied.The results show that the pulse width mainly affects the porosity and internal stress of DLC films,which in turn brings about differences in surface morphology and corrosion resistance.The implanted ion energy of DLC film deposition ions decreases with the increase of pulse width.The DLC film prepared under 20?s grows by surface diffusion,and the film is loose and porous and has poor corrosion resistance.The DLC film prepared under 15?s has greater energy for ion implantation,the growth mode is changed to subsurface implantation,and the film has high density and strong corrosion resistance.The density of the DLC film prepared under 10?s continues to increase,but the internal stress also becomes greater,and the influence of stress corrosion cracking will reduce the corrosion resistance of the DLC film.The effects of different bias voltages on the local corrosion and uniform corrosion behavior of DLC films were studied.The results show that different bias voltages lead to significant differences in the hydrogen content and sp~2 hybrid structure content of the film,which in turn leads to significant differences in corrosion resistance and surface morphology after corrosion.The more hydrogen content,the greater the probability of local corrosion of the film and the more pitting corrosion pits.The more sp~2 hybrid structure content,the greater the film conductivity,the worse the uniform corrosion resistance,and the larger the pit diameter.The wear-corrosion behavior and crevice corrosion behavior of DLC films doped with silicon are studied under a constant temperature of 37?and an environment that simulates human body fluids.The results show that the Si-DLC film has good corrosion resistance,and the performance of the DLC and Si-DLC film after wear corrosio is still better than that of the 316L substrate without wear corrosion.Although the Si-DLC film is worn over a large area,the protection of the film to the substrate still exists.The DLC film suffered severe pitting and lost its protective effect on the substrate.Crevice corrosion obviously occurs,and the corrosion behavior of different crevice depths is significantly different.The corrosion at the mouth of the crevice is more serious.The corrosion of the film deep in the crevice is reduced,and the surface is scaly.