Abstract
Using embedded atom method potential, extensive large-scale molecular dynamics (MD) simulations of nanoindentation/nanoscratching of nanocrystalline (nc) iron have been carried out to explore grain size dependence of wear response. MD results show no clear dependence of the frictional and normal forces on the grain size, and the single-crystal (sc) iron has higher frictional and normal force compared to nc-samples. For all samples, the dislocation-mediated mechanism is the primary cause of plastic deformation in both nanoindentation/nanoscratch. However, secondary cooperative mechanisms are varied significantly according to grain size. Pileup formation was observed in the front of and sideways of the tool, and they exhibit strong dependence on grain orientation rather than grain size. Tip size has significant impact on nanoscratch characteristics; both frictional and normal forces monotonically increase as tip radii increase, while the friction coefficient value drops by about 38%. Additionally, the increase in scratch depth leads to an increase in frictional and normal forces as well as friction coefficient. To elucidate the relevance of indentation/scratch results with mechanical properties, uniaxial tensile test was performed for nc-samples, and the result indicates the existence of both the regular and inverse Hall–Petch relations at critical grain size of 110.9 Å. The present results suggest that indentation/scratch hardness has no apparent correlation with the mechanical properties of the substrate, whereas the plastic deformation has.
Highlights
Understanding wear, friction and mechanical properties of a material at nanoscale is crucial for further development in technological applications
They demonstrated that the primary mechanism for nanoscale wear of silicon carbide is grain boundaries (GBs) sliding and the compatible stress is accommodated by nucleation of partial dislocations, void formation and grains pullout
We have performed large-scale molecular dynamics simulations of single-asperity nanoscratch of nanocrystalline iron to investigate the effect of grain size, tip radius and scratch depth on its wear behavior
Summary
Understanding wear, friction and mechanical properties of a material at nanoscale is crucial for further development in technological applications. Molecular dynamics simulation has been used to investigate nanoscale machining and the factors governing the nanomachining process: tip geometry, machining speed, rake angle and surface roughness Most of these simulations usually adopt defect-free monocrystalline structures as the work material [3,4,5,6,7,8,9]. It was discovered that for all cutting conditions simulated, the polycrystalline structure requires smaller cutting forces compared with the monocrystalline structure The authors attributed this behavior to the reduction in material strength with grain refinement. Mishra et al [18] simulated the wear of a nanocrystalline silicon carbide substrate by tools with a rounded end They demonstrated that the primary mechanism for nanoscale wear of silicon carbide is GBs sliding and the compatible stress is accommodated by nucleation of partial dislocations, void formation and grains pullout. We can find optimized conditions for improved wear resistance of nc-iron
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