Molecular dynamics simulation of the nano-cutting mechanism of a high-phosphorus NiP coating

Abstract

Electroless nickel-phosphorus workpieces undergo a variety of surface/subsurface deformations and internal organizational changes throughout the nano-cutting process that have a major impact on the machining quality of microstructured functional surfaces. In this paper, molecular dynamics simulations were performed for nano-cutting of electroless nickel-phosphorus (Ni–P) workpieces obtained at different cooling rates (1e11 K/s, 1e12 K/s, 1e13 K/s). To research the mechanisms of material removal and surface formation during nano-cutting, the impacts of various cutting depths on atomic ordering, cutting force, cutting temperature, shear strain, material pile-up, and surface shape were examined. The simulations showed that material removal of NiP coatings was mainly based on nanoscale extrusion rather than macroscale shear. The radial distribution function of NiP coatings was dominated by the Ni–P pair, the cutting force of the nano-cutting process was more stable, the thrust force was smaller, and the machined surface roughness Ra was smaller when the cooling rate was higher. However, the number of atoms on the upper surface of the workpiece increased more, and the actual machined surface contour line deviated from the ideal surface contour when the cooling rate was faster. To increase the forming accuracy of the machined surface on NiP without destroying the machined surface roughness, the cooling rate must be slowed appropriately for the NiP alloy to form a tiny amount of crystalline organization or to minimize the nano-cutting depth.