Deviation of mechanical behavior in microforming from continuum scaling: A geometrically necessary dislocation storage perspective. (October 2021)

• Record Type: Journal Article
• Authors: Zhang, Bin; Meng, Andrew C.; Meng, W.J.
• Is Part Of: International journal of machine tools & manufacture. Volume 169(2021)
• Publication Date: 2021-10
• Subjects: Mesoscale reverse extrusion -- Microscale molding -- Grain size effect -- Geometrically necessary dislocation storage; Machine-tools -- Periodicals; Manufacturing processes -- Periodicals; Machines-outils -- Périodiques; Fabrication -- Périodiques; Electronic journals; 621.902
• DOI: 10.1016/j.ijmachtools.2021.103795
• Languages: English
• ISSNs: 0890-6955

Abstract

Abstract: Meso-/micro-scale metal forming offers problems in which the characteristic deformation length scale can approach the grain size of the material being formed. In this regime, the mechanical response of the deformed material exhibits various deviations from conventional continuum plasticity. This paper shows two such examples involving polycrystalline Cu with different grain sizes. In mesoscale axisymmetric reverse extrusion, Cu with a larger grain size requires a higher scaled pressure to extrude. In microscale double-punch molding, Cu with a larger grain size flows less into micron sized gaps as compared to Cu with a smaller grain size. In both cases, the trend expected from ranking of the bulk flow stress is reversed. To understand these phenomena, we quantitatively analyze crystallographic orientation data obtained from electron backscatter diffraction scans on thin material slices extracted from as-extruded and as-molded Cu specimens. The results show that, for both deformation geometries, Cu with the larger grain size stored more geometrically necessary dislocations under the same deformation geometry. The influence of grain size on geometrically necessary dislocation storage during forming offers a unified, structure-based rationale for the observed anomalous mechanical behavior. This storage is likely influenced by an interplay between the deformation geometry, the characteristic deformation length scale, and the grain size. Graphical abstract: Image 1 Highlights: Deviation of microforming mechanical response from expected conventional continuum plasticity behavior documented in detail EBSD data analysis for deformed Cu conducted using a newly devised method and quantitative results on GND storage obtained Observed anomalous mechanical behavior linked to storage of geometrically necessary dislocations within deformed Cu