Tribocorrosion Behaviors Of 45# Steel And Its Surface Carbon-based Film In Methanol Solution

Methanol fuel is vigorously promoted because it meets the development requirements of energy saving and emission reduction,but the combustion of methanol produces substances such as formic acid,formaldehyde and water,which cause corrosion and wear to metal parts and become a key problem restricting the development of methanol fuel.The preparation of thin films or coatings on the surface of metal parts with both corrosion and wear resistance is one of the possible methods.Diamond-like carbon（Diamond-like carbon,DLC）films are of great interest to the materials community because of their high hardness,low friction,excellent wear resistance and good corrosion resistance.The excellent properties of DLC films make their application in methanol environment feasible,however,few research works related to this issue have been reported.Therefore,in this paper,45#steel was selected as the substrate material,and non-hydrogen DLC films and hydrogen-containing DLC films（H-DLC）were prepared on its surface by non-equilibrium magnetron sputtering technique.The microstructure,morphology and their mechanical properties of the two DLC films were analyzed separately,and the corrosion and wear performance and mechanism of 45#steel and the two different DLC coatings in methanol solution were investigated.The main work and conclusions of this paper are as follows:（1）Combined with friction and wear test,electrochemical test and morphology characterization,the effects of applied load,friction frequency and formic acid content on the corrosion and wear properties of 45#steel in methanol environment were analyzed.The results show that the average friction coefficient of DLC film friction and wear is between0.05 and 0.1,which is only about 1/10 of the 45#steel substrate under the same conditions,and the volume wear rate is also reduced by an order of magnitude.Compared with the friction and wear experiments,the average friction coefficients of DLC films under different loads,friction frequencies and formic acid contents were further reduced due to the presence of methanol solution.The volume wear rate of the DLC film is further reduced to about 1/2 of that under friction and wear conditions.The electrochemical results show that the DLC film has good corrosion resistance in methanol solution containing formic acid,which effectively blocks the acid corrosion that occurs when the corrosive medium contacts the substrate.Due to the high chemical inertness,the wear of DLC films in methanol solution is mainly caused by ordinary mechanical wear.（2）The effects of load,friction frequency and formic acid content on the friction and wear properties and corrosion and wear properties of non-hydrogen DLC films were studied.The results show that the wear rate of friction and wear of DLC film is one order of magnitude lower than that of the substrate,and the wear rate of corrosion wear is further reduced.The electrochemical results show that the DLC film has good corrosion resistance in methanol solution containing formic acid,which effectively blocks the acid corrosion that occurs when the corrosive medium contacts the substrate.Due to the high chemical inertness,the wear of DLC films in methanol solution is mainly caused by ordinary mechanical wear.（3）The effects of load,friction frequency and formic acid content on the friction,wear and corrosion wear properties of H-DLC films were investigated.The results show that the average friction coefficient of the H-DLC film under different loads and friction frequencies is between 0.15 and 0.25,which is higher than that of the non-hydrogen DLC film,but its volume wear rate is 1/2 of that of the non-hydrogen DLC film,and it has better performance.Friction and wear resistance.The H-DLC films exhibited good corrosion and wear resistance in methanol solution,mainly manifested as low friction coefficient（0.02-0.08）and wear rate(10^-7mm³·N^-1·m^-1order of magnitude).Electrochemical test results show that H-DLC films exhibit better corrosion resistance in corrosive media due to their good densification and passivation effect（high sp3 C content）compared to non-hydrogen DLC films.