Anisotropy is one central influencing factor on achievable ultimate machined surface integrity of metallic materials.Specifically,grain boundary has a strong impact on the deformation behaviour of polycrystalline mate...Anisotropy is one central influencing factor on achievable ultimate machined surface integrity of metallic materials.Specifically,grain boundary has a strong impact on the deformation behaviour of polycrystalline materials and correlated material removal at the microscale.In the present work,we perform molecular dynamics simulations and experiments to elucidate the underlying grain boundaryassociated mechanisms and their correlations with machining results of a bi-crystal Cu under nanocutting using a Berkovich tool.Specifically,crystallographic orientations of simulated bi-crystal Cu with a misorientation angle of 44.1°are derived from electron backscatter diffraction characterization of utilized polycrystalline copper specimen.Simulation results reveal that blocking of dislocation motion at grain boundaries,absorption of dislocations by grain boundaries and dislocation nucleation from grain boundaries are operating deformation modes in nanocutting of the bi-crystal Cu.Furthermore,heterogeneous grain boundary-associated mechanisms in neighbouring grains lead to strong anisotropic machining behaviour in the vicinity of the grain boundary.Simulated machined surface morphology and machining force evolution in the vicinity of grain boundary qualitatively agree well with experimental results.It is also found that the geometry of Berkovich tool has a strong impact on grain boundary-associated mechanisms and resultant ploughing-induced surface pile-up phenomenon.展开更多
Nanomanipulation plays an important role in nanofabrication, it is also a technology necessary in exploring the secrets of nanoworld, and it thus becomes a start point to research future nanomachine. In this study, ma...Nanomanipulation plays an important role in nanofabrication, it is also a technology necessary in exploring the secrets of nanoworld, and it thus becomes a start point to research future nanomachine. In this study, manipulation and cutting of carbon nanotubes have been conducted in order to examine whether we can move a nano-component from one site to another by using the tip of atomic force microscope (AFM). The technique may also be valuable for providing the constructive materials of nanofabrication. While exploring the method for manipulating and cutting of nanotubes, some new phenomena have been observed during the process. Results show that carbon nanotubes present a feature of deformation combining bending and distortion when subjected to large mechanical forces exerted by the tip of AFM. In special cases, long carbon nanotubes can be cut into two parts, by which we can remove the part where crystal lattice is flawed, and therefore a perfect nanocomponent can be obtained.展开更多
基金The authors greatly acknowledge support from the Science Challenge Project(Nos.TZ2018006-0201-02 and TZ2018006-0205-02)the Fundamental Research Funds for the Central Universities.
文摘Anisotropy is one central influencing factor on achievable ultimate machined surface integrity of metallic materials.Specifically,grain boundary has a strong impact on the deformation behaviour of polycrystalline materials and correlated material removal at the microscale.In the present work,we perform molecular dynamics simulations and experiments to elucidate the underlying grain boundaryassociated mechanisms and their correlations with machining results of a bi-crystal Cu under nanocutting using a Berkovich tool.Specifically,crystallographic orientations of simulated bi-crystal Cu with a misorientation angle of 44.1°are derived from electron backscatter diffraction characterization of utilized polycrystalline copper specimen.Simulation results reveal that blocking of dislocation motion at grain boundaries,absorption of dislocations by grain boundaries and dislocation nucleation from grain boundaries are operating deformation modes in nanocutting of the bi-crystal Cu.Furthermore,heterogeneous grain boundary-associated mechanisms in neighbouring grains lead to strong anisotropic machining behaviour in the vicinity of the grain boundary.Simulated machined surface morphology and machining force evolution in the vicinity of grain boundary qualitatively agree well with experimental results.It is also found that the geometry of Berkovich tool has a strong impact on grain boundary-associated mechanisms and resultant ploughing-induced surface pile-up phenomenon.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 50075043, 50135040 and 50173001)the Doctorate Designation Fund of the Ministry of Education of China (Grant No. 2000000339).
文摘Nanomanipulation plays an important role in nanofabrication, it is also a technology necessary in exploring the secrets of nanoworld, and it thus becomes a start point to research future nanomachine. In this study, manipulation and cutting of carbon nanotubes have been conducted in order to examine whether we can move a nano-component from one site to another by using the tip of atomic force microscope (AFM). The technique may also be valuable for providing the constructive materials of nanofabrication. While exploring the method for manipulating and cutting of nanotubes, some new phenomena have been observed during the process. Results show that carbon nanotubes present a feature of deformation combining bending and distortion when subjected to large mechanical forces exerted by the tip of AFM. In special cases, long carbon nanotubes can be cut into two parts, by which we can remove the part where crystal lattice is flawed, and therefore a perfect nanocomponent can be obtained.
