Physiochemical effect on the microgroove microstructure in microcutting of pure copper

The physiochemical effect on the microcutting of pure copper is studied through characterization on the cross-sectioned microgroove. An obvious reduction in cutting force and thrust force can be obtained with the application of ink surfactant. The surface roughness of microgroove with physiochemical effect is 12 nm, and that without physiochemical effect is 17 nm. The average grain size of the ink-affected sample is 67.9 µm within the microgroove zone, and that of the ink-free sample is 48.3 µm within the microgroove zone, moreover, the grain size of ink-free microgroove near the microgroove surface is larger than that far away from the microgroove surface. Additionally, the grain orientations of ink-affected cross-sectioned surface present anisotropy, while that of ink-free cross-sectioned surface are towards {101} direction. Based on the calculation and analysis of geometrically necessary dislocation, it can be inferred that the induced stress and temperature in the sample with physiochemical effect are higher than that without physiochemical effect, which can provide enough driving energy for recrystallization.

Physiochemical effect on the microgroove microstructure in microcutting of pure copper

Physiochemical effect on the machining of pure copper is studied via microstructure characterization on the cross-sectioned microgroove. An obvious decreased cutting force and thrust force were obtained with the application of surfactant. The surface roughness of microgroove with physiochemical effect is 12 nm, and that without physiochemical effect is 17 nm. The average grain size of the medium-affected sample is 67.9 µm within the microgroove zone, and that of the medium-free sample is 48.3 µm within the microgroove zone, moreover, the grain size of medium-free microgroove near the microgroove surface is larger than that far away from the microgroove surface. Additionally, the grain orientations of medium-affected cross-sectioned surface present anisotropy, while that of medium-free cross-sectioned surface are towards {101} direction. Based on the calculation and analysis of geometrically necessary dislocation, it can be inferred that the induced stress and temperature in the sample with physiochemical effect are higher than that without physiochemical effect, which can provide enough driving energy for recrystallization.

The indentation size effect of single-crystalline tungsten revisited

In this study, we have investigated the indentation size effect (ISE) of single crystalline tungsten with low defect density. As expected, the hardness shows a pronounced increase with decreasing indentation depth as well as a strong strain rate dependence. For penetration depths greater than about 300 nm, the ISE is well captured by the Nix–Gao model in the context of geometrically necessary dislocations. However, clear deviations from the model are observed in the low depth regime resulting in a bilinear effect. The hardness behavior in the low depth regime can be modeled assuming a non-uniform spacing of the geometrically necessary dislocations. We propose that the bilinear indentation size effect observed reflects the evolution of the geometrically necessary dislocation density. With increasing strain rate, the bilinear effect becomes less pronounced. This observation can be rationalized by the activation of different slip systems. Graphic abstract

Length-Scale-Dependent Micromechanical Modeling for Precipitate Hardening in Inconel 718 Superalloy

In this paper, a micromechanical finite element (FE) model has been proposed to investigate the effect of the nanoscale precipitates on the development of microplasticity for Inconel 718 (IN718) superalloy. A strain gradient crystal plasticity formulation has been developed with the considerations of the evolution of statistically stored dislocation density and geometrically necessary dislocation density. The mesh convergence has been examined, showing that sufficiently fine mesh is required in the FE model. The results show that the model with strain gradient effect incorporated shows less peak plastic strain and higher value of dislocation density than the model with no strain gradient effect. The present study indicates that the strain hardening process at the scale of strengthening precipitate is mainly governed by the evolution of geometrically necessary dislocation densities.