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Advances in the use of in situ transmission electron microscopy (TEM) to study mechanical deformation have enabled a direct correlation of mechanical properties with microstructures, in particular, atomic-level defect dynamic processes. Shear deformation of metallic materials has been noticed to lead to unique microstructural features with superior properties that would be difficult to achieve by traditional metallurgical processes. However, in contrast to the case of in situ TEM studies of structural evolution under tension, compression, and bending, in situ TEM probing of dynamic processes during direct shear loading, especially at microscales and nanoscales, is very limited. This paper reviews recent progress on the development of in situ TEM for studying shear deformation in terms of both the technique and the scientific insights that have been gained. In addition, we discuss current challenges encountered in the use of in situ TEM for shear deformation, such as the limited total strain, strain rate, and spatial and temporal resolution. To provide perspective, we present promising opportunities for in situ TEM studies with pure shear loading by taking advantage of the integration of advanced imaging techniques both in TEM and scanning transmission electron microscopy domains, advanced electron detectors, highly efficient chemical analysis, data-driven machine learning, and environmental conditions. [ABSTRACT FROM AUTHOR]

The role of deformation twinning in the formation of a fine-grained structure in cold-rolled 310S steels has been investigated by using transmission electron microscopy. When 310S steels were rolled at room temperature, a deformation twin appeared in the early stage of the rolling process. A fine lamellar structure consisting of the deformation twin and matrix (T-M) developed with increased rolling strain. At moderate strain, micro shear bands appeared in the area of the T-M lamellar structure, and the shear bands grew and multiplied during further cold-rolling. Such multiplication of shear bands destroyed the T-M lamellar structure, which caused the development of a fine-grained structure. In shear bands, a highly misoriented structure with a submicron grain size was generated. In this paper, the mechanism of the transmutation process from the T-M lamellae into the fine-grained structure is discussed. Particular emphasis is laid on the role of deformation twinning in the formation of the fine-grained structure. [ABSTRACT FROM AUTHOR]

The accommodation of severe plastic deformation in impact crater formation, ballistic rod flow and penetration in thick targets, shaped charge formation, and a variety of friction-stir welding and processing is shown to occur by microstructure refinement, particularly dynamic recrystallization in the development of localized or overlapping adiabatic shear bands. Optical metallography and transmission electron microscopy observations of solid-state flow in adiabatic shear zones are compared to illustrate these mechanisms which can often involve intermixed microstructural regimes composed of recovery, recrystallization, and grain growth phenomena. [ABSTRACT FROM AUTHOR]

Single crystals of a Cu-Fe alloy, which contained spherical γ-Fe particles, were compressed up to shear strain of 0.17 in liquid nitrogen bath. In the process of straining the structural (optical and TEM) observations in as-deformed and post-deformation annealed samples were provided. The substructure of deformed samples was characterized by slightly developed cell structure and lack of distinct layer-like arrangements of dislocations. Three kinds of particles were found: coherent and semi-coherent f.c.c. γ-Fe and martensiticly transformed b.c.c. α-Fe. The critical diameter for coherency loss was found to be 58 nm at the initial stage of deformation decreasing with strain to 50 nm. These values coincided with the theoretical estimations. It was suggested that relaxation of coherency strains around γ-Fe particles by the generation of interface dislocations might occur prior to the martensitic transformation. This assumption might explain the particle size dependency of martensitic transformation. [ABSTRACT FROM AUTHOR]