Atomistic Investigation of the Grain Boundary Effect on Fracture Mechanisms in BCC Fe Bamboolike Polycrystal Nanowire

MM Rahman and AKM Ashikuzzaman and R Saha, PROCEEDINGS OF THE 13TH INTERNATIONAL CONFERENCE ON MECHANICAL ENGINEERING (ICME2019), 2324, 030021 (2021).

DOI: 10.1063/5.0037716

Nanowires (NWs) have many enhanced properties such as high yield strength, high ductility and large elongation under tensile loading. Though many molecular dynamics simulations have been performed exhibiting the benefit of having grain boundaries in nanowires, this study focuses on the mechanical properties of a specific grain formation similar to a structure of bamboo that indicates the opposite phenomena. In this experiment, BCC Fe nanowires were strained under tensile loading and with the assistance of molecular dynamics simulation it was demonstrated that the behavior of polycrystalline Fe NW exhibits dramatic differences from their single crystalline NW counterparts. In single crystalline Fe NW, dislocations were generated from the surface in the directions of specific planes for BCC materials; whereas in the case of nanowire with bamboolike polycrystalline shape, dislocation were generated from grain boundary due to the localized high stress and the heterogeneous character of atoms in the grain boundary. Ultimate strengths for <111>, <1-1-2>, <102> and <110> oriented single crystal NWs were found 34.57 GPa, 19.15 GPa, 14.94 GPa and 25.48 GPa respectively. A substantial low strength (8.89 GPa) was observed for the polycrystalline Fe structure, which was mainly caused due to the deformation in the interface of the two subsequent grains. Necking was observed followed by fracture, resulting in an overall drop in toughness. These findings can be a matter of concern in certain applications where materials with high strength and stability are required.

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