Friction And Wear Behaviors Of Diamond-Like Carbon Films In Acidic Corrosive Media

Stainless steel owns excellent corrosion resistance and plays an extremely important role in petrochemical,construction,machinery manufacturing and other industries.However,mechanical equipments made of stainless steel in the interaction of corrosive media and tribocorrosion still face severe challenges.For example,hydrochloric acid（HCl）and sulfuric acid（H₂SO₄）,as important chemical raw materials,show more serious corrosion tendency to metal parts.And the production,storage,transportation and reprocessing of the HCl and H₂SO₄are inseparable from bearings,valves,blades made of stainless steel.These key parts usually face the problem of being susceptible to corrosion and wear failure,which will not only cause a certain economic loss,but also cause unpredictable major disaster.Therefore,it is very important to develop a protective method for the surface of mechanical parts made of stainless steel in an acid corrosion environment.It should not only meet the resistance requirements against acid corrosion media,but also have good wear resistance.At present,it is one of the feasible methods to prepare coatings or films with corrosion resistance and wear resistance on the surface of stainless steel parts.Diamond-like carbon（DLC）has high hardness,low friction,wear resistance and good chemical stability,which provides feasibility for its application in harsh corrosive environments.However,there are few related reports on research work.Based on above,this work selected 304 stainless steel as substract material,and used unbalanced magnetron sputtering（UBMS）technology to prepare four DLC films on the substract surface.The friction and wear performances of four films in HCl environment were comparatively studied.After that,the tribological mechanisms of DLC film in HCl and H₂SO₄environments were further explored.It is expected that this work can provide theoretical basis and technical support for the application of DLC film on the surface of 304 stainless steel parts in acid environments.The main research contents and conclusions of this paper are summarized as follows:1)The DLC,Cr/DLC,H/DLC and WC/DLC films were prepared on the surface of 304stainless steel using UBMS technology,and the friction and wear behaviors of the four films in1 M HCl solution were investigated by combining the microstructure analysis,mechanical property characterization and electrochemical test.The results show that element doping is beneficial to reduce the surface roughness of DLC films.Among them,the surface morphology of the H/DLC film is densest and smoothest.Besides,the H/DLC film has higher sp³ C content,while the Cr/DLC and WC/DLC films have higher sp² C content.Finally,the wear mechanism of DLC film in HCl solution is solid-liquid lubrication wear,the wear of Cr/DLC film in HCl is dominated by abrasive wear,the wear of H/DLC film in HCl is coordinated by adhesion wear and abrasive wear,the wear of WC/DLC film in HCl is co-dominated by abrasive wear and tribochemical wear.2)The friction and wear performances and corrosion resistance of 304 stainless steel and DLC film in 1 M HCl and 0.5 M H₂SO₄ were comparatively studied using NaCl solution and deionized water as the reference environments.And the tribological mechanisms of DLC film in HCl and H₂SO₄ solution were exploxed.The results indicated that DLC film presented the lowest friction coefficient and wear rate in 1 M HCl solution,which might be attributed to the boundary lubrication of HCl and tribochemical products,as well as lubrication of graphitization.While the relatively higher friction coefficient and wear rate of DLC film in 0.5 M H₂SO₄solution were mainly related to the smaller graphitization,higher viscosity and adhesive wear of debris cluster.The pitting effect of Cl^-on DLC film was boosted in 1 M HCl solution due to the enlarged hole of H⁺,resulting in the corrosion resistance of DLC film in 1 M HCl solution become worse.Compared with NaCl solution and deionized water,the wear of DLC film in HCl and H₂SO₄ solution.Accordingly,DLC film can significantly improve the resistance of wear and corrosion of 304 stainless steel in HCl and H₂SO₄ solution,which fully indicates that DLC film can be used as a protective layer for the application of 304 stainless steel in acid environments.