Surface Quality And Subsurface Damage Of Monocrystalline Nickel Nanomachining

Adapting for the development tendency of product microminiaturization and highprecision,the technology of micro-nano processing and manufacturing has been increasingly applied in precision machining,such as manufacture of nano-optical instrument and nano-electronic device.However,the limits of the experimental equipment and condition,make the control of the existing methods of nanomachining difficult,leading to the misjudgment of testing result which affected by the system characteristics or the experimental impurities.Meanwhile,real-time nanomachining process can hardly be observed and detected dynamically.Influenced by size effect,quantum effect and surface effect,the machining mechanism at nanoscale is different from conventional machining.In this paper,research on the nanomachining mechanism of monocrystalline nickel in atomicity is conducted via molecular dynamics.By the molecular dynamics modeling,the displacement of surface atoms,the morphology of machined surface,the structure of subsurface defects and other machined mechanisms during the processing are revealed.And then the nanoscale scratch experiments are conducted to validate the simulation results.The research illustrates the machining mechanism of monocrystalline nickel,which simultaneously provides theoretical foundation for the development of nanomachining technology.In the first part of the paper,the nano-grinding models of monocrystalline nickel are established via three-dimensional molecular dynamics modeling at various speeds and depths.According to the displacement variation of surface atoms in grinding process,the formation mechanism of surface and subsurface in nanomachining is revealed.Combined with crystal defect identification technology,the changes in the surface morphology,subsurface damage and grinding force during the process are analyzed.The simulation results show that the grinding speed has little effect on the surface morphology of monocrystalline nickel,while the speed increase improves subsurface damage when the grinding enters ultra-high speed stage.In conclusion,ultra-high grinding speed and small grinding depth in nanomachining can achieve better machined surface quality and less subsurface defects.In above study,the nano-grinding process is conducted along the(100)plane at various speeds and depths.But as a face-centered cubic crystal,the monocrystalline nickel has three typical faces: 100,110,111.Thus in the second part of the paper,the nano-grinding of monocrystalline nickel is conducted in other crystal faces along with different crystal orientations via molecular dynamics modeling.The simulation shows the knowledge of crystallography can well explain the angle formed in the slip path,which leading to height changes of the grinding burrs formed by discharged chips.Based on the changing curve of atomic potential energy from selected workpiece atoms,the result is calculated that the depth of monocrystalline nickel subsurface deformation layer reaches the minimum when the grinding is conducted along the direction of(111)[?110].Concurrently,the research find that the diameter of grinding grain has great effect on the machined surface quality of monocrystalline nickel.And the changes of grain diameter can be converted into different effective rake angles of the grinding tool.Hence,in the third part of the paper,the nanomachining mechanism of monocrystalline nickel affected by different rake angles,clearance angles and blunt radiuses of the grinding tool is analyzed.Consequently,the research proves that the toughness of machined surface reaches the minimum when the rake angle at 30° or-30°.Meanwhile,when the negative rake angle is adding,the tangential force on the tool increases accordingly.While the change of blunt radius has little effect on the tangential force.Moreover,the concept of critical zone of clearance angle is proposed in the paper.The change of clearance angle hardly effects on machined surface beyond its critical zone.According to the calculation,the critical zone of monocrystalline nickel is 8°-10° when the grinding depth is 1 nm.In addition,aiming at analyzing the effect of pre-process to subsequent processes,multiple nanomachining procedures,such as repeated machining,are simulated via molecular dynamics in the paper,leading to the result that the integrity of machined surface in monocrystalline nickel grinding can be improved when the pre-process is conducted before the grinding.Concurrently,the existence of pre-process impacts on the depth of subsurface deformation layer generated by grinding,while secondary repeated machining can improve the damage of subsurface.On the contrary,triple repeated machining or more has little effect on the subsurface defects and reduces the machining efficiency.Finally,the nano-scratch experiment is conducted by the removal of monocrystalline nickel to validate the results of molecular dynamics modeling in the paper.The result demonstrates that in the nanomanchining process,monocrystalline nickel is insensitive to the variation of grinding speed,which is in accord with molecular dynamics simulation.Moreover,in the experiment of scratching on three different crystal faces,the tangential force is the smallest when scratching on the crystal face(111),validating the result of molecular dynamics modeling.The paper contributes to the research of nanomachining mechanism of monocrystalline nickel.By molecular dynamics modeling and nano-scratch experiments,the formation mechanism of machined surface and subsurface damages in the nano-grinding process of monocrystalline nickel are revealed and analyzed,simultaneously providing theoretical foundation for the processing technic optimization and the machining precision improvement of monocrystalline nickel.