The passivation of hydrogen atoms and the conformation of textured surfaces under oil-lubricated conditions are effective strategies to obtain amorphous carbon(a-C)films with extremely low friction.It is critical to u...The passivation of hydrogen atoms and the conformation of textured surfaces under oil-lubricated conditions are effective strategies to obtain amorphous carbon(a-C)films with extremely low friction.It is critical to understanding the influence mechanism of selective surface hydrogenation on the tribological behaviors of textured a-C film under oil-lubricated conditions.In particular,the interactions of hydrogen atoms and lubricants are confusing,which is enslaved to the in situ characterization technique.The reactive molecular dynamics(RMD)simulations were conducted to analyze the friction response of textured a-C films with selective hydrogenation surfaces under oil-lubricated conditions.The results indicate that the existence of hydrogen atoms on specific bump sites significantly decreases the friction coefficient(μ)of textured a-C film,which is highly dependent on the surface hydrogen content.The repulsion between hydrogen atoms and lubricant molecules prompts the formation of a dense lubricant film on the surface of the mating material.Interestingly,with the enhancement of the surface hydrogen content,the passivation of the friction interface and the repulsion between hydrogen atoms and lubricants play dominant roles in reducing the friction coefficient instead of hydrodynamic lubrication.展开更多
Current tribocorrosion research of metallic materials and their surface protective coatings mainly focuses on their short-term properties,with test time of 0.5‒2.0 h and a sliding distance 50‒500 m,which may significa...Current tribocorrosion research of metallic materials and their surface protective coatings mainly focuses on their short-term properties,with test time of 0.5‒2.0 h and a sliding distance 50‒500 m,which may significantly deviate from the practical long-term service condition and thus cause a catastrophe of marine equipments.In this study,three carbon-based multilayer coatings(Ti/DLC,TiC_(x)/DLC,and Ti‒TiC_(x)/DLC)were deposited on S32750 substrates,and both short-term and long-term tribocorrosion behaviors were investigated.The experimental results indicate that the coatings substantially improve the tribocorrosion resistance of the S32750 stainless steel.During the short-term tribocorrosion test,TiC_(x)/DLC exhibited the best tribocorrosion resistance owing to its high hardness.During the long-term tribocorrosion test,however,Ti‒TiC_(x)/DLC coating indicated the best anti-tribocorrosion performance owing to its excellent fracture toughness together with high hardness.Moreover,under 5 N,Ti‒TiC_(x)/DLC can withstand a long-term test of more than 24 h.Additionally,under a higher load of 20 N,the Ti‒TiC_(x)/DLC with a corresponding sliding distance of approximately 1,728 m maintained a low friction coefficient of approximately 0.06.However,the coating was completely worn out;this is attributable to the formation of tribocorrosion products consisting of graphitized carbon and nanocrystalline Fe_(x)O_(y).展开更多
Combining an amorphous carbon(a-C)film with a lubricating oil can significantly improve the friction performance and lifetime of moving mechanical components.However,the friction mechanism is not well understood owing...Combining an amorphous carbon(a-C)film with a lubricating oil can significantly improve the friction performance and lifetime of moving mechanical components.However,the friction mechanism is not well understood owing to a lack of information regarding the structure of the interface when exposed to high contact pressure.Here,we select linear alpha olefin,C5H10,as a lubricant and study the evolution of the structure of the a-C/C5H10/a-C sliding interface under contact pressure via reactive molecular dynamics simulation.Our results suggest that introducing C5H10 into the a-C/a-C interface reduces the friction coefficient by up to 93% compared with no lubricant,although the lubricating efficiency strongly depends on the contact pressure.In particular,increasing the contact pressure not only induces the binding of the lubricant with a-C,but also facilitates the dissociation of the C5H10 carboncarbon skeleton by specific scissions,which governs the friction behavior.These results disclose the underlying lubrication mechanism and could enable the development of new and effective lubricating systems with long lifetimes.展开更多
Surface graphitization is an effective method for improving the friction performance of amorphous carbon(a-C)films.However,traditional modified methods,such as metal catalysis,addition of extra graphite or graphene,an...Surface graphitization is an effective method for improving the friction performance of amorphous carbon(a-C)films.However,traditional modified methods,such as metal catalysis,addition of extra graphite or graphene,and annealing,often have drawbacks,such as complex operation,structural damage to the graphitized layer and intrinsic a-C films.In this study,a novel approach is explored to achieve in-situ surface graphitization of a-C films by short-term laser irradiation.In particular,as a key parameter,the influence of laser irradiation power on the surface graphitization structure and the mechanical and tribological properties of a-C films was emphasized.The results indicate that surface in-situ graphitization is successfully obtained on the surface of a-C films by laser irradiation and the surface graphitization degree is positively correlated with the laser irradiation power.Importantly,an obviously curled graphene structure is formed on the a-C films after laser irradiation.Compared with those of the intrinsic a-C film,the hardness and elastic modulus of the graphitized film surface obviously decrease after laser irradiation but without significantly deteriorated internal mechanical properties of the a-C film and also decrease gradually with increasing laser power,which is related to the increase in the sp2-C structure.Notably,in-situ surface graphitization induced by laser irradiation obviously reduces friction,which can be reduced by 25.41%compared with the intrinsic a-C film.This is attributed to the fast formation of the graphitized transfer film,which facilitates the transition of the friction interface from graphitized a-C surface/Al2O3 to graphitized a-C surface/graphitized transfer film.展开更多
基金financially supported by the National Natural Science Foundation of China(No.52175204)Basic Research Program of Xuzhou(No.KC21041)+2 种基金Material Science and Engineering Discipline Guidance Fund of China University of Mining and Technology(No.CUMTMS202211)Graduate Innovation Program of China University of Mining and Technology(No.2022WLJCRCZL281)Jiangsu Funding Program for Excellent Postdoctoral Talent(No.2022ZB522).
文摘The passivation of hydrogen atoms and the conformation of textured surfaces under oil-lubricated conditions are effective strategies to obtain amorphous carbon(a-C)films with extremely low friction.It is critical to understanding the influence mechanism of selective surface hydrogenation on the tribological behaviors of textured a-C film under oil-lubricated conditions.In particular,the interactions of hydrogen atoms and lubricants are confusing,which is enslaved to the in situ characterization technique.The reactive molecular dynamics(RMD)simulations were conducted to analyze the friction response of textured a-C films with selective hydrogenation surfaces under oil-lubricated conditions.The results indicate that the existence of hydrogen atoms on specific bump sites significantly decreases the friction coefficient(μ)of textured a-C film,which is highly dependent on the surface hydrogen content.The repulsion between hydrogen atoms and lubricant molecules prompts the formation of a dense lubricant film on the surface of the mating material.Interestingly,with the enhancement of the surface hydrogen content,the passivation of the friction interface and the repulsion between hydrogen atoms and lubricants play dominant roles in reducing the friction coefficient instead of hydrodynamic lubrication.
基金This work was supported by the National Natural Science Foundation of China(Nos.52025014 and 51801226)A-class pilot of the Chinese Academy of Sciences(No.XDA22010303)+2 种基金K.C.Wong Education Foundation(No.GJTD-2019-13)CAS-NST Joint Research Project(No.174433KYSB20200021)CAS Interdisciplinary Innovation Team(No.292020000008).
文摘Current tribocorrosion research of metallic materials and their surface protective coatings mainly focuses on their short-term properties,with test time of 0.5‒2.0 h and a sliding distance 50‒500 m,which may significantly deviate from the practical long-term service condition and thus cause a catastrophe of marine equipments.In this study,three carbon-based multilayer coatings(Ti/DLC,TiC_(x)/DLC,and Ti‒TiC_(x)/DLC)were deposited on S32750 substrates,and both short-term and long-term tribocorrosion behaviors were investigated.The experimental results indicate that the coatings substantially improve the tribocorrosion resistance of the S32750 stainless steel.During the short-term tribocorrosion test,TiC_(x)/DLC exhibited the best tribocorrosion resistance owing to its high hardness.During the long-term tribocorrosion test,however,Ti‒TiC_(x)/DLC coating indicated the best anti-tribocorrosion performance owing to its excellent fracture toughness together with high hardness.Moreover,under 5 N,Ti‒TiC_(x)/DLC can withstand a long-term test of more than 24 h.Additionally,under a higher load of 20 N,the Ti‒TiC_(x)/DLC with a corresponding sliding distance of approximately 1,728 m maintained a low friction coefficient of approximately 0.06.However,the coating was completely worn out;this is attributable to the formation of tribocorrosion products consisting of graphitized carbon and nanocrystalline Fe_(x)O_(y).
基金This work was supported by the Korea Research Fellowship Program funded by the Ministry of Science and ICT through the National Research Foundation of Korea(2017H1D3A1A01055070)the Nano Materials Research Program through the Ministry of Science and IT Technology(NRF-2016M3A7B4025402)the National Natural Science Foundation of China(51772307,51522106).
文摘Combining an amorphous carbon(a-C)film with a lubricating oil can significantly improve the friction performance and lifetime of moving mechanical components.However,the friction mechanism is not well understood owing to a lack of information regarding the structure of the interface when exposed to high contact pressure.Here,we select linear alpha olefin,C5H10,as a lubricant and study the evolution of the structure of the a-C/C5H10/a-C sliding interface under contact pressure via reactive molecular dynamics simulation.Our results suggest that introducing C5H10 into the a-C/a-C interface reduces the friction coefficient by up to 93% compared with no lubricant,although the lubricating efficiency strongly depends on the contact pressure.In particular,increasing the contact pressure not only induces the binding of the lubricant with a-C,but also facilitates the dissociation of the C5H10 carboncarbon skeleton by specific scissions,which governs the friction behavior.These results disclose the underlying lubrication mechanism and could enable the development of new and effective lubricating systems with long lifetimes.
基金financially supported by the National Natural Science Foundation of China(Nos.52175204 and 52305237)the Innovation Team of Jiangsu Province(No.JSSCTD202241)+1 种基金the Foreign Expert Program of the Ministry of Science and Technology of China(No.G2023142001L)the Open Fund of the State Key Laboratory of Solid Lubrication,Lanzhou Institute of Chemical Physics,Chinese Academy of Sciences(No.LSL-2310).
文摘Surface graphitization is an effective method for improving the friction performance of amorphous carbon(a-C)films.However,traditional modified methods,such as metal catalysis,addition of extra graphite or graphene,and annealing,often have drawbacks,such as complex operation,structural damage to the graphitized layer and intrinsic a-C films.In this study,a novel approach is explored to achieve in-situ surface graphitization of a-C films by short-term laser irradiation.In particular,as a key parameter,the influence of laser irradiation power on the surface graphitization structure and the mechanical and tribological properties of a-C films was emphasized.The results indicate that surface in-situ graphitization is successfully obtained on the surface of a-C films by laser irradiation and the surface graphitization degree is positively correlated with the laser irradiation power.Importantly,an obviously curled graphene structure is formed on the a-C films after laser irradiation.Compared with those of the intrinsic a-C film,the hardness and elastic modulus of the graphitized film surface obviously decrease after laser irradiation but without significantly deteriorated internal mechanical properties of the a-C film and also decrease gradually with increasing laser power,which is related to the increase in the sp2-C structure.Notably,in-situ surface graphitization induced by laser irradiation obviously reduces friction,which can be reduced by 25.41%compared with the intrinsic a-C film.This is attributed to the fast formation of the graphitized transfer film,which facilitates the transition of the friction interface from graphitized a-C surface/Al2O3 to graphitized a-C surface/graphitized transfer film.
