Although atomic stick–slip friction has been extensively studied since its first demonstration on graphite,the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we p...Although atomic stick–slip friction has been extensively studied since its first demonstration on graphite,the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we perform molecular dynamics（MD） simulations to study the frictional behavior of a diamond tip sliding over a graphite surface. In contrast to the common wisdom, our MD results suggest that the energy barrier associated lateral sliding（known as energy corrugation） comes not only from interaction between the tip and the top layer of graphite but also from interactions among the deformed atomic layers of graphite. Due to the competition of these two subentries, friction on graphite can be tuned by controlling the relative adhesion of different interfaces.For relatively low tip-graphite adhesion, friction behaves normally and increases with increasing normal load. However,for relatively high tip-graphite adhesion, friction increases unusually with decreasing normal load leading to an effectively negative coefficient of friction, which is consistent with the recent experimental observations on chemically modified graphite. Our results provide a new insight into the physical origins of energy corrugation in atomic scale friction.展开更多
The mechanisms of energy dissipation are discussed in this paper by reviewing the models and research in atomic-scale friction.The study is undertaken to answer a fundamental question in the study of friction:How is f...The mechanisms of energy dissipation are discussed in this paper by reviewing the models and research in atomic-scale friction.The study is undertaken to answer a fundamental question in the study of friction:How is frictional work dissipated,particularly in cases where material damage and wear are not involved.The initiation of energy dissipation,the role of structural commensurability,and the estimation of the interfacial shear strength have been examined in detail by introducing the Tomlinson model,the Frenkel-Kontorova model,and the cobblestone model,respectively.The discussion is extended to energy dissipation progress described in terms of phononic and electronic damping.The contributions from other mechanisms of dissipation such as viscoelastic relaxation and material wear are also included.As an example,we analyzed a specific process of dissipation in multilayer graphene,on the basis of results of molecular dynamics(MD)simulations,which reveal a reversible part of energy that circulates between the system and the external driver.This leads us to emphasize that it is crucial in future studies to clearly define the coefficient of dissipation.展开更多
The energy transition and dissipation of atomic-scale friction are investigated using the one-dimensional Prandtl-Tomlinson model.A systematic study of the factors influencing the energy dissipation is conducted,indic...The energy transition and dissipation of atomic-scale friction are investigated using the one-dimensional Prandtl-Tomlinson model.A systematic study of the factors influencing the energy dissipation is conducted,indicating that the energy that accumulated during the stick stage does not always dissipate completely during stick-slip motion.We adopt the energy-dissipation ratio(EDR)to describe the relationship between the energy dissipated permanently in the system and the conservative reversible energy that can be reintroduced to the driving system after the slip process.The EDR can change continuously from 100%to 0,covering the stick-slip,intermediate,and smooth-sliding regimes,depending on various factors such as the stiffness,potential-energy corrugation,damping coefficient,sliding velocity,and the temperature of the system.Among these,the parameterη,which depends on both the surface potential and the lateral stiffness,is proven in this paper to have the most significant impact on the EDR.According toη-T phase diagrams of the EDR,the smooth-sliding superlubricity and thermolubricity are found to be unified with regard to the energy dissipation and transition.An analytical formulation for the EDR that can be used to quantitatively predict the amount of energy dissipation is derived from a lateral-force curve.展开更多
The highly efficient manufacturing of atomic-scale smooth β-Ga_(2)O_(3)surface is fairly challenging because β-Ga_(2)O_(3)is a typical difficult-to-machine material.In this study,a novel plasma dry etching method na...The highly efficient manufacturing of atomic-scale smooth β-Ga_(2)O_(3)surface is fairly challenging because β-Ga_(2)O_(3)is a typical difficult-to-machine material.In this study,a novel plasma dry etching method named plasma-based atom-selective etching(PASE)is proposed to achieve the highly efficient,atomic-scale,and damage-free polishing of β-Ga_(2)O_(3).The plasma is excited through the inductive coupling principle and carbon tetrafluoride is utilized as the main reaction gas to etch β-Ga_(2)O_(3).The core of PASE polishing of β-Ga_(2)O_(3)is the remarkable lateral etching effect,which is ensured by both the intrinsic property of the surface and the extrinsic temperature condition.As revealed by density functional theory-based calculations,the intrinsic difference in the etching energy barrier of atoms at the step edge(2.36 eV)and in the terrace plane(4.37 eV)determines their difference in the etching rate,and their etching rate difference can be greatly enlarged by increasing the extrinsic temperature.The polishing of β-Ga_(2)O_(3)based on the lateral etching effect is further verified in the etching experiments.The Sa roughness of β-Ga_(2)O_(3)(001)substrate is reduced from 14.8 nm to 0.057 nm within 120 s,and the corresponding material removal rate reaches up to 20.96μm·min^(−1).The polished β-Ga_(2)O_(3)displays significantly improved crystalline quality and photoluminescence intensity,and the polishing effect of PASE is independent of the crystal face of β-Ga_(2)O_(3).In addition,the competition between chemical etching and physical reconstruction,which is determined by temperature and greatly affects the surface state of β-Ga_(2)O_(3),is deeply studied for the first time.These findings not only demonstrate the high-efficiency and high-quality polishing of β-Ga_(2)O_(3)via atmospheric plasma etching but also hold significant implications for guiding future plasma-based surface manufacturing of β-Ga_(2)O_(3).展开更多
Atomic-level manufacturing,as the "keystone" of future technology,marks the transformative shift from the micro/nano era based on "classical theory" to the atomic era grounded in "quantum theo...Atomic-level manufacturing,as the "keystone" of future technology,marks the transformative shift from the micro/nano era based on "classical theory" to the atomic era grounded in "quantum theory".It enables the precise control of matter arrangement and composition at the atomic scale,thereby achieving large-scale production of atomically precise and structured products.Electrochemical deposition(ECD),a typical "atom addition" fabrication method for electrochemical atomic and close-to-atomic scale manufacturing(EC-ACSM),enables precise control over material properties at the atomic scale,allowing breakthroughs in revolutionary performance of semiconductors,quantum computing,new materials,nanomedicine,etc.This review explores the fundamentals of EC-ACSM,particularly at the electrode/electrolyte interface,and investigates maskless ECD techniques,highlighting their advantages,limitations,and the role of in situ monitoring and advanced simulations in the process optimization.However,atomic electrochemical deposition faces significant challenges in precise control over atom-ion interactions,electrode-electrolyte interfacial dynamics,and surface defects.In the future,overcoming these obstacles is critical to advancing EC-ACSM and unlocking its full potential in scalability for industrial applications.EC-ACSM can drive the highly customized design of materials and offer strong technological support for the development of future science,ushering in a new atomic era of material innovation and device manufacturing.展开更多
Molecular dynamics simulations have been performed to explore the atomic-scale sliding friction, especially the stick-slip friction, in a system consisting of a diamond slider and a silver substrate. The mechanisms of...Molecular dynamics simulations have been performed to explore the atomic-scale sliding friction, especially the stick-slip friction, in a system consisting of a diamond slider and a silver substrate. The mechanisms of the stick-slip behavior are investigated by considering sliding speeds between 10 m/s and 200 m/s.The analyses of the shear distance between the upmost layer and the downmost layer and displacements of a column of atoms in the slider show that shearing deformation of the slider is the main cause of the stick-slip phenomenon. Our simulations also present that a commensurate fit between the two contact surfaces is unimportant for the stick-slip friction.展开更多
Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing addit...Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing additive-induced defects,and alleviating residual stress and deformation,all of which are critical for enhancing the mechanical performance of the manufactured parts.Integrating interlayer friction stir processing(FSP)into WAAM significantly enhances the quality of deposited materials.However,numerical simulation research focusing on elucidating the associated thermomechanical coupling mechanisms remains insufficient.A comprehensive numerical model was developed to simulate the thermomechanical coupling behavior in friction stir-assisted WAAM.The influence of post-deposition FSP on the coupled thermomechanical response of the WAAM process was analyzed quantitatively.Moreover,the residual stress distribution and deformation behavior under both single-layer and multilayer deposition conditions were investigated.Thermal analysis of different deposition layers in WAAM and friction stir-assisted WAAM was conducted.Results show that subsequent layer deposition induces partial remelting of the previously solidified layer,whereas FSP does not cause such remelting.Furthermore,thermal stress and deformation analysis confirm that interlayer FSP effectively mitigates residual stresses and distortion in WAAM components,thereby improving their structural integrity and mechanical properties.展开更多
This paper provides a fresh perspective and new insights into nanoscale friction by investigating it through molecular dynamics(MD)simulation and atomic force microscope(AFM)nanoscratch experiments.This work considere...This paper provides a fresh perspective and new insights into nanoscale friction by investigating it through molecular dynamics(MD)simulation and atomic force microscope(AFM)nanoscratch experiments.This work considered gallium arsenide,an importantⅢ-Ⅴdirect bandgap semiconductor material residing in the zincblende structure,as a reference sample material due to its growing usage in 5G communication devices.In the simulations,the scratch depth was tested as a variable in the fine range of 0.5-3 nm to understand the behavior of material removal and to gain insights into the nanoscale friction.Scratch force,normal force,and average cutting forces were extracted from the simulation to obtain two scalar quantities,namely,the scratch cutting energy(defined as the work performed to remove a unit volume of material)and the kinetic coefficient of friction(defined as the force ratio).A strong size effect was observed for scratch depths below 2 nm from the MD simulations and about 15 nm from the AFM experiments.A strong quantitative corroboration was obtained between the specific scratch energy determined by the MD simulations and the AFM experiments,and more qualitative corroboration was derived for the pile-up and the kinetic coefficient of friction.This conclusion suggests that the specific scratch energy is insensitive to the tool geometry and the scratch speed used in this investigation.However,the pile-up and kinetic coefficient of friction are dependent on the geometry of the tool tip.展开更多
The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural ...The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.展开更多
The correlation betweent deformation behavior and atomic-scale heterogeneity of bulk metallic glasses(BMGs)is critical to understand the BMGs'deformation mechanism.In this work,three typical[(Fe_(0.5)Co_(0.5))_(0....The correlation betweent deformation behavior and atomic-scale heterogeneity of bulk metallic glasses(BMGs)is critical to understand the BMGs'deformation mechanism.In this work,three typical[(Fe_(0.5)Co_(0.5))_(0.75)B_(0.2)Si_(0.05)]_(96)Nb_4,Fe_(39)Ni_(39)B_(14.2)Si_(2.75)P_(2.75)Nb_(2.3),and Fe_(50)Ni_(30)P_(13)C_(7)BMGs exhibiting different plasticity were selected,and the correlation between deformation behavior and atomic-scale heterogeneity of Fe-based BMGs was studied.It is found that the serrated flow dynamics of Fe-based BMGs transform from chaotic state to self-organized critical state with increasing plasticity.This transformation is attributed to the increasing atomic-scale heterogeneity caused by the increasing free volume and short-to-medium range order,which facilitates a higher frequency of interaction and multiplication of shear bands,thereby results in a brittle to ductile transition in Fe-based BMGs.This work provides new evidence on heterogeneity in plastic Fe-based BMGs from the aspects of atomic-scale structure,and provides new insight into the plastic deformation of Fe-based BMGs.展开更多
Atomic and close-to-atomic scale manufacturing(ACSM)aims to provide techniques for manufacturing in various fields,such as circuit manufacturing,high energy physics equipment,and medical devices and materials.The real...Atomic and close-to-atomic scale manufacturing(ACSM)aims to provide techniques for manufacturing in various fields,such as circuit manufacturing,high energy physics equipment,and medical devices and materials.The realization of atomic scale material manipulation depending on the theoretical system of classical mechanics faces great challenges.Understanding and using intermolecular and surface forces are the basis for better designing of ACSM.Transformation of atoms based on scanning tunneling microscopy or atomic force microscopy(AFM)is an essential process to regulate intermolecular interactions.Self-assemble process is a thermodynamic process involving complex intermolecular forces.The competition of these interaction determines structure assembly and packing geometry.For typical nanomachining processes including AFM nanomachining and chemical mechanical polishing,the coupling of chemistry and stress(tribochemistry)assists in the removal of surface atoms.Furthermore,based on the principle of triboelectrochemistry,we expect a further reduction of the potential barrier,and a potential application in high-efficiency atoms removal and fabricating functional coating.Future fundamental research is proposed for achieving high-efficiency and high-accuracy manufacturing with the aiding of external field.This review highlights the significant contribution of intermolecular and surface forces to ACSM,and may accelerate its progress in the in-depth investigation of fundamentals.展开更多
The intrinsic origins and formation of atomic-scale structure in multicomponent alloys remain largely unknown owing to limited simulations and inaccessible experiments.Herein,we report the formation of three-dimension...The intrinsic origins and formation of atomic-scale structure in multicomponent alloys remain largely unknown owing to limited simulations and inaccessible experiments.Herein,we report the formation of three-dimensional periodicity from a disordered atomic-scale structure to an imperfect/perfect ordered cluster and finally to long-range translational and rotational symmetry coupled with Nb heterogeneity.Significant atomic-scale structural clustering and atomic arrangements involving solvent or solute atoms simultaneously occurred during isothermal annealing.A close relationship between atomic-scale structural evolution and composition variation has important implications in depicting the chemical and topological packing during the early crystallization stage in metallic glasses.This work can provide a comprehensive understanding of how short-range orders evolve into long-range periodicity and will further shed light on the origins and nature of metallic glasses.展开更多
Nanocrystalline metals have many functional and structural applications due to their excellent mechanical properties compared to their coarse-grained counterparts. The atomic-scale understanding of the deformation mec...Nanocrystalline metals have many functional and structural applications due to their excellent mechanical properties compared to their coarse-grained counterparts. The atomic-scale understanding of the deformation mechanisms of nanocrystalline metals is important for designing new materials, novel structures and applications. The review presents recent developments in the methods and techniques for in situ deformation mechanism investigations on face-centered-cubic nanocrystalline metals. In the first part,we will briefly introduce some important techniques that have been used for investigating the deformation behaviors of nanomaterials. Then, the size effects and the plasticity behaviors in nanocrystalline metals are discussed as a basis for comparison with the plasticity in bulk materials. In the last part, we show the atomic-scale and time-resolved dynamic deformation processes of nanocrystalline metals using our in-lab developed deformation device.展开更多
The signs of the electric field markers in Figs.2 and 4 of the paper[Chin.Phys.B 32104211(2023)]have been corrected.These modifications do not affect the results derived in the paper.
Atoms in the microscopic world are the basic building blocks of the macroscopic world. In this work, we construct an atomic-scale electromagnetic theory that bridges optics in the microscopic and macroscopic worlds. A...Atoms in the microscopic world are the basic building blocks of the macroscopic world. In this work, we construct an atomic-scale electromagnetic theory that bridges optics in the microscopic and macroscopic worlds. As the building block of the theory, we use the microscopic polarizability to describe the optical response of a single atom, solve the transport of electromagnetic wave through a single atomic layer under arbitrary incident angle and polarization of the light beam, construct the single atomic layer transfer matrix for light transport across the atomic layer. Based on this transfer matrix, we get the analytical form of the dispersion relation, refractive index, and transmission/reflection coefficient of the macroscopic medium. The developed theory can handle single-layer and few-layers of homogeneous and heterogeneous 2D materials, investigate homogeneous 2D materials with various vacancies or insertion atomic-layer defects, study compound 2D materials with a unit cell composed of several elements in both the lateral and parallel directions with respect to the light transport.展开更多
At present,the emerging solid-phase friction-based additive manufacturing technology,including friction rolling additive man-ufacturing(FRAM),can only manufacture simple single-pass components.In this study,multi-laye...At present,the emerging solid-phase friction-based additive manufacturing technology,including friction rolling additive man-ufacturing(FRAM),can only manufacture simple single-pass components.In this study,multi-layer multi-pass FRAM-deposited alumin-um alloy samples were successfully prepared using a non-shoulder tool head.The material flow behavior and microstructure of the over-lapped zone between adjacent layers and passes during multi-layer multi-pass FRAM deposition were studied using the hybrid 6061 and 5052 aluminum alloys.The results showed that a mechanical interlocking structure was formed between the adjacent layers and the adja-cent passes in the overlapped center area.Repeated friction and rolling of the tool head led to different degrees of lateral flow and plastic deformation of the materials in the overlapped zone,which made the recrystallization degree in the left and right edge zones of the over-lapped zone the highest,followed by the overlapped center zone and the non-overlapped zone.The tensile strength of the overlapped zone exceeded 90%of that of the single-pass deposition sample.It is proved that although there are uneven grooves on the surface of the over-lapping area during multi-layer and multi-pass deposition,they can be filled by the flow of materials during the deposition of the next lay-er,thus ensuring the dense microstructure and excellent mechanical properties of the overlapping area.The multi-layer multi-pass FRAM deposition overcomes the limitation of deposition width and lays the foundation for the future deposition of large-scale high-performance components.展开更多
Friction stir lap welding of AA2195 Al-Li alloy and Ti alloy was conducted to investigate the formation,microstructure,and mechanical properties of the joints.Results show that under different welding parameters,with ...Friction stir lap welding of AA2195 Al-Li alloy and Ti alloy was conducted to investigate the formation,microstructure,and mechanical properties of the joints.Results show that under different welding parameters,with the decrease in welding heat input,the weld surface is smoother.The Ti/Al joint interface is flat without obvious Ti and Al mixed structure,and the hook structure is not formed under optimal parameters.Due to the enhanced breaking effect of the stirring head,the hook structural defects and intermetallic compounds are more likely to form at the Ti/Al interface at high rotational speed of 1000 r/min,thereby deteriorating the mechanical properties of joints.Decreasing the heat input is beneficial to hardness enhancement of the aluminum alloy in the weld nugget zone.Under the optimal parameters of rotation speed of 800 r/min and welding speed of 120 mm/min,the maximum tensile shear strength of joint is 289 N/mm.展开更多
The composite structures/components made by friction stir lap welding(FSLW)of Mg alloy sheet and Al alloy sheet are of wide application potentials in the manufacturing sector of transportation vehicles.To further impr...The composite structures/components made by friction stir lap welding(FSLW)of Mg alloy sheet and Al alloy sheet are of wide application potentials in the manufacturing sector of transportation vehicles.To further improve the joint quality,the ultrasonic vibration(UV)is exerted in FSLW,and the UV enhanced FSLW(UVeFSLW)was developed for making Mg-to-Al dissimilar joints.The numerical analysis and experimental investigation were combined to study the process mechanism in Mg/Al UVeFSLW.An equation related to the temperature and strain rate was derived to calculate the grain size at different locations of the weld nugget zone,and the effect of grain size distribution on the threshold thermal stress was included,so that the prediction accuracy of flow stress was further improved.With such modified constitutive equation,the numerical simulation was conducted to compare the heat generation,temperature profiles and material flow behaviors in Mg/Al UVeFSLW/FSLW processes.It was found that the exerted UV decreased the temperature at two checking points on the tool/workpiece interface from 707/671 K in FSLW to 689/660 K in UVeFSLW,which suppressed the IMCs thickness at Mg-Al interface from 1.7μm in FSLW to 1.1μm in UVeFSLW.The exerted UV increased the horizontal materials flow ability,and decreased the upward flow ability,which resulted in the increase of effective sheet thickness/effective lap width from 2.01/3.70 mm in FSLW to 2.04/4.84 mm in UVeFSLW.Therefore,the ultrasonic vibration improved the tensile shear strength of Mg-to-Al lap joints by 18%.展开更多
GH4169 joints manufactured by Linear Friction Welding(LFW)are subjected to tensile test and stair-case method to evaluate the High Cycle Fatigue(HCF)performance at 650℃.The yield and ultimate tensile strengths are 58...GH4169 joints manufactured by Linear Friction Welding(LFW)are subjected to tensile test and stair-case method to evaluate the High Cycle Fatigue(HCF)performance at 650℃.The yield and ultimate tensile strengths are 582 MPa and 820 MPa,respectively.The HCF strength of joint reaches 400 MPa,which is slightly lower than that of Base Metal(BM),indicating reliable quality of this type of joint.The microstructure observation results show that all cracks initiate at the inside of specimens and transfer into deeper region with decrease of external stress,and the crack initiation site is related with microhardness of matrix.The Electron Backscattered Diffraction(EBSD)results of the observed regions with different distances to fracture show that plastic deformation plays a key role in HCF,and the Schmid factor of most grains near fracture exceeds 0.4.In addition,the generation of twins plays a vital role in strain concentration release and coordinating plastic deformation among grains.展开更多
基金support from the National Natural Science Foundation of China (Grants 11272177, 11422218, 11432008)the National Basic Research Program of China (Grants 2013CB933003, 2013CB934201 and 2015CB351903)+2 种基金the Tsinghua University Initiative Scientific Research Programthe Thousand Young Talents Program of Chinathe financial support from China Postdoctoral Science Foundation (Grant 2014M562055)
文摘Although atomic stick–slip friction has been extensively studied since its first demonstration on graphite,the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we perform molecular dynamics（MD） simulations to study the frictional behavior of a diamond tip sliding over a graphite surface. In contrast to the common wisdom, our MD results suggest that the energy barrier associated lateral sliding（known as energy corrugation） comes not only from interaction between the tip and the top layer of graphite but also from interactions among the deformed atomic layers of graphite. Due to the competition of these two subentries, friction on graphite can be tuned by controlling the relative adhesion of different interfaces.For relatively low tip-graphite adhesion, friction behaves normally and increases with increasing normal load. However,for relatively high tip-graphite adhesion, friction increases unusually with decreasing normal load leading to an effectively negative coefficient of friction, which is consistent with the recent experimental observations on chemically modified graphite. Our results provide a new insight into the physical origins of energy corrugation in atomic scale friction.
基金The authors would like to express their appreciations to the financial support from the National Natural Science Foundation of China under the grant Nos.of 51075526,51005129,and 51021064.
文摘The mechanisms of energy dissipation are discussed in this paper by reviewing the models and research in atomic-scale friction.The study is undertaken to answer a fundamental question in the study of friction:How is frictional work dissipated,particularly in cases where material damage and wear are not involved.The initiation of energy dissipation,the role of structural commensurability,and the estimation of the interfacial shear strength have been examined in detail by introducing the Tomlinson model,the Frenkel-Kontorova model,and the cobblestone model,respectively.The discussion is extended to energy dissipation progress described in terms of phononic and electronic damping.The contributions from other mechanisms of dissipation such as viscoelastic relaxation and material wear are also included.As an example,we analyzed a specific process of dissipation in multilayer graphene,on the basis of results of molecular dynamics(MD)simulations,which reveal a reversible part of energy that circulates between the system and the external driver.This leads us to emphasize that it is crucial in future studies to clearly define the coefficient of dissipation.
基金supported by the National Natural Science Foundation of China(Grant Nos.51422504,51375010,and 51371092)the National Key Basic Research(973)Program of China(No.2013CB934200).
文摘The energy transition and dissipation of atomic-scale friction are investigated using the one-dimensional Prandtl-Tomlinson model.A systematic study of the factors influencing the energy dissipation is conducted,indicating that the energy that accumulated during the stick stage does not always dissipate completely during stick-slip motion.We adopt the energy-dissipation ratio(EDR)to describe the relationship between the energy dissipated permanently in the system and the conservative reversible energy that can be reintroduced to the driving system after the slip process.The EDR can change continuously from 100%to 0,covering the stick-slip,intermediate,and smooth-sliding regimes,depending on various factors such as the stiffness,potential-energy corrugation,damping coefficient,sliding velocity,and the temperature of the system.Among these,the parameterη,which depends on both the surface potential and the lateral stiffness,is proven in this paper to have the most significant impact on the EDR.According toη-T phase diagrams of the EDR,the smooth-sliding superlubricity and thermolubricity are found to be unified with regard to the energy dissipation and transition.An analytical formulation for the EDR that can be used to quantitatively predict the amount of energy dissipation is derived from a lateral-force curve.
基金supported by the National Natural Science Foundation of China(52375437,52035009)the Natural Science Foundation of Guangdong Province(2024B1515020027)+2 种基金the Shenzhen Science and Technology Program(Grant No.KQTD20170810110250357)for the financial supportthe assistance of SUSTech Core Research Facilitiessupported by Shenzhen Engineering Research Center for Semiconductorspecific Equipment。
文摘The highly efficient manufacturing of atomic-scale smooth β-Ga_(2)O_(3)surface is fairly challenging because β-Ga_(2)O_(3)is a typical difficult-to-machine material.In this study,a novel plasma dry etching method named plasma-based atom-selective etching(PASE)is proposed to achieve the highly efficient,atomic-scale,and damage-free polishing of β-Ga_(2)O_(3).The plasma is excited through the inductive coupling principle and carbon tetrafluoride is utilized as the main reaction gas to etch β-Ga_(2)O_(3).The core of PASE polishing of β-Ga_(2)O_(3)is the remarkable lateral etching effect,which is ensured by both the intrinsic property of the surface and the extrinsic temperature condition.As revealed by density functional theory-based calculations,the intrinsic difference in the etching energy barrier of atoms at the step edge(2.36 eV)and in the terrace plane(4.37 eV)determines their difference in the etching rate,and their etching rate difference can be greatly enlarged by increasing the extrinsic temperature.The polishing of β-Ga_(2)O_(3)based on the lateral etching effect is further verified in the etching experiments.The Sa roughness of β-Ga_(2)O_(3)(001)substrate is reduced from 14.8 nm to 0.057 nm within 120 s,and the corresponding material removal rate reaches up to 20.96μm·min^(−1).The polished β-Ga_(2)O_(3)displays significantly improved crystalline quality and photoluminescence intensity,and the polishing effect of PASE is independent of the crystal face of β-Ga_(2)O_(3).In addition,the competition between chemical etching and physical reconstruction,which is determined by temperature and greatly affects the surface state of β-Ga_(2)O_(3),is deeply studied for the first time.These findings not only demonstrate the high-efficiency and high-quality polishing of β-Ga_(2)O_(3)via atmospheric plasma etching but also hold significant implications for guiding future plasma-based surface manufacturing of β-Ga_(2)O_(3).
基金the support from the National Natural Science Foundation of China (Grant Nos. 52405447 and 52275299)the National Key Research and Development Program of China (Grant No. 2021YFB1716200)the Key Research and Development Program of Jiangxi Province in China (Grant No. 20232BBE50011)。
文摘Atomic-level manufacturing,as the "keystone" of future technology,marks the transformative shift from the micro/nano era based on "classical theory" to the atomic era grounded in "quantum theory".It enables the precise control of matter arrangement and composition at the atomic scale,thereby achieving large-scale production of atomically precise and structured products.Electrochemical deposition(ECD),a typical "atom addition" fabrication method for electrochemical atomic and close-to-atomic scale manufacturing(EC-ACSM),enables precise control over material properties at the atomic scale,allowing breakthroughs in revolutionary performance of semiconductors,quantum computing,new materials,nanomedicine,etc.This review explores the fundamentals of EC-ACSM,particularly at the electrode/electrolyte interface,and investigates maskless ECD techniques,highlighting their advantages,limitations,and the role of in situ monitoring and advanced simulations in the process optimization.However,atomic electrochemical deposition faces significant challenges in precise control over atom-ion interactions,electrode-electrolyte interfacial dynamics,and surface defects.In the future,overcoming these obstacles is critical to advancing EC-ACSM and unlocking its full potential in scalability for industrial applications.EC-ACSM can drive the highly customized design of materials and offer strong technological support for the development of future science,ushering in a new atomic era of material innovation and device manufacturing.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 50730007, 50675111 and 50721004)National Basic Research Program of China (Grant No. 2009CB724200)
文摘Molecular dynamics simulations have been performed to explore the atomic-scale sliding friction, especially the stick-slip friction, in a system consisting of a diamond slider and a silver substrate. The mechanisms of the stick-slip behavior are investigated by considering sliding speeds between 10 m/s and 200 m/s.The analyses of the shear distance between the upmost layer and the downmost layer and displacements of a column of atoms in the slider show that shearing deformation of the slider is the main cause of the stick-slip phenomenon. Our simulations also present that a commensurate fit between the two contact surfaces is unimportant for the stick-slip friction.
基金National Key Research and Development Program of China(2022YFB4600902)Shandong Provincial Science Foundation for Outstanding Young Scholars(ZR2024YQ020)。
文摘Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing additive-induced defects,and alleviating residual stress and deformation,all of which are critical for enhancing the mechanical performance of the manufactured parts.Integrating interlayer friction stir processing(FSP)into WAAM significantly enhances the quality of deposited materials.However,numerical simulation research focusing on elucidating the associated thermomechanical coupling mechanisms remains insufficient.A comprehensive numerical model was developed to simulate the thermomechanical coupling behavior in friction stir-assisted WAAM.The influence of post-deposition FSP on the coupled thermomechanical response of the WAAM process was analyzed quantitatively.Moreover,the residual stress distribution and deformation behavior under both single-layer and multilayer deposition conditions were investigated.Thermal analysis of different deposition layers in WAAM and friction stir-assisted WAAM was conducted.Results show that subsequent layer deposition induces partial remelting of the previously solidified layer,whereas FSP does not cause such remelting.Furthermore,thermal stress and deformation analysis confirm that interlayer FSP effectively mitigates residual stresses and distortion in WAAM components,thereby improving their structural integrity and mechanical properties.
基金The authors would like to thank EPSRC(EP/K018345/1,EP/T024844/1)the Royal Society-NSFC Interna-tional Exchange Program(IECINSFC181474)for providing financial support to this research.SG is particularly thankful for the research support provided by the UKRI via Grant Nos.EP/L016567/1,EP/S013652/1,EP/T001100/1,EP/S036180/1,and EP/T024607/1+4 种基金The authors also acknowledge the support received from H2020(Cost Actions CA18125,CA18224,CA17136,and CA16235)the Royal Academy of Engineering via Grant Nos.IAPP18-19)295,TSP1332,and EXPP2021\11277and the Newton Fellowship award from the Royal Society(NIFR1191571)SG also accessed the Isambard Bris-tol,a UK supercomputing service,via the Resource Allocation Panel and ARCHER2 resources(Project e648)The authors also acknowledge the use of the EPSRC(EP/K000586/1)-funded ARCHIE WeSt High-Performance Computer at the University of Strathclyde.
文摘This paper provides a fresh perspective and new insights into nanoscale friction by investigating it through molecular dynamics(MD)simulation and atomic force microscope(AFM)nanoscratch experiments.This work considered gallium arsenide,an importantⅢ-Ⅴdirect bandgap semiconductor material residing in the zincblende structure,as a reference sample material due to its growing usage in 5G communication devices.In the simulations,the scratch depth was tested as a variable in the fine range of 0.5-3 nm to understand the behavior of material removal and to gain insights into the nanoscale friction.Scratch force,normal force,and average cutting forces were extracted from the simulation to obtain two scalar quantities,namely,the scratch cutting energy(defined as the work performed to remove a unit volume of material)and the kinetic coefficient of friction(defined as the force ratio).A strong size effect was observed for scratch depths below 2 nm from the MD simulations and about 15 nm from the AFM experiments.A strong quantitative corroboration was obtained between the specific scratch energy determined by the MD simulations and the AFM experiments,and more qualitative corroboration was derived for the pile-up and the kinetic coefficient of friction.This conclusion suggests that the specific scratch energy is insensitive to the tool geometry and the scratch speed used in this investigation.However,the pile-up and kinetic coefficient of friction are dependent on the geometry of the tool tip.
基金supported by the National Natural Science Foundation of China (Nos. 52075449, 51975480)。
文摘The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding(RFSSW),and the microstructural evolution and corrosion behavior of the joints were investigated.Based on microstructural analysis,the welded joints exhibit distinct microstructural zones,including the stir zone(SZ),thermomechanically affected zone(TMAZ),and heat-affected zone(HAZ).The grain size of each zone is in the order of HAZ>TMAZ>SZ.Notably,the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ,with particle size in the HAZ increasing at higher rotational speeds.Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ>TMAZ>SZ>BM,with greater sensitivity observed at increased rotational speeds.Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps,but not from the changes in the microstructure.
基金supported by the National Natural Science Foundation of China(Grant Nos.51631003 and 51871054)the Fundamental Research Funds for the Central Universities(Grant No.2242019k1G005)supported by the Department of Energy(DOE)Office of Science(DE-AC02-06CH11357)。
文摘The correlation betweent deformation behavior and atomic-scale heterogeneity of bulk metallic glasses(BMGs)is critical to understand the BMGs'deformation mechanism.In this work,three typical[(Fe_(0.5)Co_(0.5))_(0.75)B_(0.2)Si_(0.05)]_(96)Nb_4,Fe_(39)Ni_(39)B_(14.2)Si_(2.75)P_(2.75)Nb_(2.3),and Fe_(50)Ni_(30)P_(13)C_(7)BMGs exhibiting different plasticity were selected,and the correlation between deformation behavior and atomic-scale heterogeneity of Fe-based BMGs was studied.It is found that the serrated flow dynamics of Fe-based BMGs transform from chaotic state to self-organized critical state with increasing plasticity.This transformation is attributed to the increasing atomic-scale heterogeneity caused by the increasing free volume and short-to-medium range order,which facilitates a higher frequency of interaction and multiplication of shear bands,thereby results in a brittle to ductile transition in Fe-based BMGs.This work provides new evidence on heterogeneity in plastic Fe-based BMGs from the aspects of atomic-scale structure,and provides new insight into the plastic deformation of Fe-based BMGs.
基金funded by the National Natural Science Foundation of China with Grant No.51425502.
文摘Atomic and close-to-atomic scale manufacturing(ACSM)aims to provide techniques for manufacturing in various fields,such as circuit manufacturing,high energy physics equipment,and medical devices and materials.The realization of atomic scale material manipulation depending on the theoretical system of classical mechanics faces great challenges.Understanding and using intermolecular and surface forces are the basis for better designing of ACSM.Transformation of atoms based on scanning tunneling microscopy or atomic force microscopy(AFM)is an essential process to regulate intermolecular interactions.Self-assemble process is a thermodynamic process involving complex intermolecular forces.The competition of these interaction determines structure assembly and packing geometry.For typical nanomachining processes including AFM nanomachining and chemical mechanical polishing,the coupling of chemistry and stress(tribochemistry)assists in the removal of surface atoms.Furthermore,based on the principle of triboelectrochemistry,we expect a further reduction of the potential barrier,and a potential application in high-efficiency atoms removal and fabricating functional coating.Future fundamental research is proposed for achieving high-efficiency and high-accuracy manufacturing with the aiding of external field.This review highlights the significant contribution of intermolecular and surface forces to ACSM,and may accelerate its progress in the in-depth investigation of fundamentals.
基金the financial support from the National Natural Science Foundation of China(Grant Nos.52074257 and 51790484)the Chinese Academy of Sciences(Grant No.ZDBSLY-JSC023)+1 种基金the Liao Ning Revitalization Talents Program(Grant Nos.XLYC1802078 and XLYC1807062)the fund of Qingdao(Grant No.19-9-2-1-wz)。
文摘The intrinsic origins and formation of atomic-scale structure in multicomponent alloys remain largely unknown owing to limited simulations and inaccessible experiments.Herein,we report the formation of three-dimensional periodicity from a disordered atomic-scale structure to an imperfect/perfect ordered cluster and finally to long-range translational and rotational symmetry coupled with Nb heterogeneity.Significant atomic-scale structural clustering and atomic arrangements involving solvent or solute atoms simultaneously occurred during isothermal annealing.A close relationship between atomic-scale structural evolution and composition variation has important implications in depicting the chemical and topological packing during the early crystallization stage in metallic glasses.This work can provide a comprehensive understanding of how short-range orders evolve into long-range periodicity and will further shed light on the origins and nature of metallic glasses.
基金supported by the Key Project of CNSF (No. 50831001)the NSFC (No. 10102001201304)+4 种基金the Beijing Nova Program (Z1511000003150142)the Beijing PXM 201101420409000053 and Beijing 211 ProjectSpecialized Research Fund for the Doctoral Program of Higher Education of China (3C102001201301)The Project of Construction of Innovative Teams and Teacher Career Development for Universities and Colleges under Beijing Municipality (IDHT20140504)the Australian Research Council (DE150101212)
文摘Nanocrystalline metals have many functional and structural applications due to their excellent mechanical properties compared to their coarse-grained counterparts. The atomic-scale understanding of the deformation mechanisms of nanocrystalline metals is important for designing new materials, novel structures and applications. The review presents recent developments in the methods and techniques for in situ deformation mechanism investigations on face-centered-cubic nanocrystalline metals. In the first part,we will briefly introduce some important techniques that have been used for investigating the deformation behaviors of nanomaterials. Then, the size effects and the plasticity behaviors in nanocrystalline metals are discussed as a basis for comparison with the plasticity in bulk materials. In the last part, we show the atomic-scale and time-resolved dynamic deformation processes of nanocrystalline metals using our in-lab developed deformation device.
文摘The signs of the electric field markers in Figs.2 and 4 of the paper[Chin.Phys.B 32104211(2023)]have been corrected.These modifications do not affect the results derived in the paper.
基金Project supported by the Guangdong Innovative and Entrepreneurial Research Team Program (Grant No. 2016ZT06C594)the Science and Technology Project of Guangdong Province of China (Grant No. 2020B010190001)+1 种基金the National Key R&D Program of China (Grant No. 2018YFA0306200)the National Natural Science Foundation of China (Grant No. 11974119)。
文摘Atoms in the microscopic world are the basic building blocks of the macroscopic world. In this work, we construct an atomic-scale electromagnetic theory that bridges optics in the microscopic and macroscopic worlds. As the building block of the theory, we use the microscopic polarizability to describe the optical response of a single atom, solve the transport of electromagnetic wave through a single atomic layer under arbitrary incident angle and polarization of the light beam, construct the single atomic layer transfer matrix for light transport across the atomic layer. Based on this transfer matrix, we get the analytical form of the dispersion relation, refractive index, and transmission/reflection coefficient of the macroscopic medium. The developed theory can handle single-layer and few-layers of homogeneous and heterogeneous 2D materials, investigate homogeneous 2D materials with various vacancies or insertion atomic-layer defects, study compound 2D materials with a unit cell composed of several elements in both the lateral and parallel directions with respect to the light transport.
基金supported by the National Key Research and Development Program of China(No.2022YFB3404700)the National Natural Science Foundation of China(Nos.52105313 and 52275299)+2 种基金the Research and Development Program of Beijing Municipal Education Commission,China(No.KM202210005036)the Natural Science Foundation of Chongqing,China(No.CSTB2023NSCQ-MSX0701)the National Defense Basic Research Projects of China(No.JCKY2022405C002).
文摘At present,the emerging solid-phase friction-based additive manufacturing technology,including friction rolling additive man-ufacturing(FRAM),can only manufacture simple single-pass components.In this study,multi-layer multi-pass FRAM-deposited alumin-um alloy samples were successfully prepared using a non-shoulder tool head.The material flow behavior and microstructure of the over-lapped zone between adjacent layers and passes during multi-layer multi-pass FRAM deposition were studied using the hybrid 6061 and 5052 aluminum alloys.The results showed that a mechanical interlocking structure was formed between the adjacent layers and the adja-cent passes in the overlapped center area.Repeated friction and rolling of the tool head led to different degrees of lateral flow and plastic deformation of the materials in the overlapped zone,which made the recrystallization degree in the left and right edge zones of the over-lapped zone the highest,followed by the overlapped center zone and the non-overlapped zone.The tensile strength of the overlapped zone exceeded 90%of that of the single-pass deposition sample.It is proved that although there are uneven grooves on the surface of the over-lapping area during multi-layer and multi-pass deposition,they can be filled by the flow of materials during the deposition of the next lay-er,thus ensuring the dense microstructure and excellent mechanical properties of the overlapping area.The multi-layer multi-pass FRAM deposition overcomes the limitation of deposition width and lays the foundation for the future deposition of large-scale high-performance components.
基金National Natural Science Foundation of China(52275349)Key Research and Development Program of Shandong Province(2021ZLGX01)。
文摘Friction stir lap welding of AA2195 Al-Li alloy and Ti alloy was conducted to investigate the formation,microstructure,and mechanical properties of the joints.Results show that under different welding parameters,with the decrease in welding heat input,the weld surface is smoother.The Ti/Al joint interface is flat without obvious Ti and Al mixed structure,and the hook structure is not formed under optimal parameters.Due to the enhanced breaking effect of the stirring head,the hook structural defects and intermetallic compounds are more likely to form at the Ti/Al interface at high rotational speed of 1000 r/min,thereby deteriorating the mechanical properties of joints.Decreasing the heat input is beneficial to hardness enhancement of the aluminum alloy in the weld nugget zone.Under the optimal parameters of rotation speed of 800 r/min and welding speed of 120 mm/min,the maximum tensile shear strength of joint is 289 N/mm.
基金supported by the National Natural Science Foundation of China(Grant No.52035005)the Key R&D Program of Shandong Province in China(Grant No.2021ZLGX01).
文摘The composite structures/components made by friction stir lap welding(FSLW)of Mg alloy sheet and Al alloy sheet are of wide application potentials in the manufacturing sector of transportation vehicles.To further improve the joint quality,the ultrasonic vibration(UV)is exerted in FSLW,and the UV enhanced FSLW(UVeFSLW)was developed for making Mg-to-Al dissimilar joints.The numerical analysis and experimental investigation were combined to study the process mechanism in Mg/Al UVeFSLW.An equation related to the temperature and strain rate was derived to calculate the grain size at different locations of the weld nugget zone,and the effect of grain size distribution on the threshold thermal stress was included,so that the prediction accuracy of flow stress was further improved.With such modified constitutive equation,the numerical simulation was conducted to compare the heat generation,temperature profiles and material flow behaviors in Mg/Al UVeFSLW/FSLW processes.It was found that the exerted UV decreased the temperature at two checking points on the tool/workpiece interface from 707/671 K in FSLW to 689/660 K in UVeFSLW,which suppressed the IMCs thickness at Mg-Al interface from 1.7μm in FSLW to 1.1μm in UVeFSLW.The exerted UV increased the horizontal materials flow ability,and decreased the upward flow ability,which resulted in the increase of effective sheet thickness/effective lap width from 2.01/3.70 mm in FSLW to 2.04/4.84 mm in UVeFSLW.Therefore,the ultrasonic vibration improved the tensile shear strength of Mg-to-Al lap joints by 18%.
基金supported by the National Natural Science Foundation of China(Nos.52074228,52305420,and 51875470)the China Postdoctoral Science Foundation(No.2023M742830)。
文摘GH4169 joints manufactured by Linear Friction Welding(LFW)are subjected to tensile test and stair-case method to evaluate the High Cycle Fatigue(HCF)performance at 650℃.The yield and ultimate tensile strengths are 582 MPa and 820 MPa,respectively.The HCF strength of joint reaches 400 MPa,which is slightly lower than that of Base Metal(BM),indicating reliable quality of this type of joint.The microstructure observation results show that all cracks initiate at the inside of specimens and transfer into deeper region with decrease of external stress,and the crack initiation site is related with microhardness of matrix.The Electron Backscattered Diffraction(EBSD)results of the observed regions with different distances to fracture show that plastic deformation plays a key role in HCF,and the Schmid factor of most grains near fracture exceeds 0.4.In addition,the generation of twins plays a vital role in strain concentration release and coordinating plastic deformation among grains.
