The cross-correlation based HR-EBSD technique was used to derive stored geometrically necessary dislocation (GND) density in the OFHC copper samples deformed under uniaxial tension to true strain of ...0%, 6%, 10%, 22.5% and 40%. Large maps (500 μm × 500 μm with 0.5 μm step size) with 1 million points and ∼1600 grains were acquired at each deformation level. Detailed studies on dislocation structure and evolution using the HR-EBSD were conducted. Distinct types of dislocation arrangements were revealed in grains with various orientations. For example, dislocation cells were formed in grains of orientation and dislocation bands were generally found in grains of and orientations. The complicated dislocation networks provide vital evidence to understand the deformation mechanisms in polycrystals at mesoscale. Quantitative analyses were also carried out to study this GND density orientation dependence in which Taylor factor was used as an indicator to quantify the grain resistance to deformation. It was found that points with high GND content preferentially accumulated in grains with high Taylor factor (‘hard’ grains) in deformed samples. This relation becomes stronger with increasing deformation.
•We recovered geometrically necessary dislocation density in deformed copper.•Dislocation networks in monotonically deformed copper were revealed.•Distinct dislocation structure was formed in grains with different orientations.•More dislocations were found near grain boundaries and triple junctions and twins.•More GNDs were stored in grains with high Taylor factor.
Understanding microstructure and its evolution is very important in safety critical components such as cladding in nuclear reactors. Zirconium alloys are used as cladding materials due to their low ...neutron capture cross section, good mechanical properties and reasonable corrosion resistance. These properties are optimised, including grain size and texture control, to maximise performance in thin (<1 mm wall thickness) tubes in water reactors. Here we show that very large grains (>0.5 mm) can be generated systematically during controlled deformation and subsequent heat treatments. We observe that the texture of these grains is controlled either by twinning or prior texture, depending on the strain path. Their nucleation, growth and texture can be controlled through strain path and deformation level. This work provides detailed understanding of the formation of these very large grains in Zircaloy-4, and also opens up opportunities for large single crystal fabrication for mm scale mechanical testing.
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Wire and arc additive manufacturing (WAAM) is a method of 3D printing that enables large elements to be built, with reasonable printing times and costs. There are, however, uncertainties relating to ...the structural performance of WAAM material, including the basic mechanical properties, the degree of anisotropy, the influence of the as-built geometry and the variability in response. Towards addressing this knowledge gap, a comprehensive series of tensile tests on WAAM stainless steel was conducted; the results are presented herein. As-built and machined coupons were tested to investigate the influence of the geometrical irregularity on the stress-strain characteristics, while material anisotropy was explored by testing coupons produced at different angles to the printing orientation. Non-contact measurement techniques were employed to determine the geometric properties and deformation fields of the specimens, while sophisticated analysis methods were used for post processing the test data. The material response revealed a significant degree of anisotropy, explained by the existence of a strong crystallographic texture, uncovered by means of electron backscatter diffraction. Finally, the effective mechanical properties of the as-built material were shown to be strongly dependent on the geometric variability; simple geometric measures were therefore developed to characterise the key aspects of the observed behaviour.
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•Results of tensile tests on WAAM stainless steel coupons are presented.•Degree of anisotropy and influence of geometric variability are examined.•Non-contact measurement methods are used to determine the geometry and deformations.•Microstructural analysis of the samples reveals a strong crystallographic texture.•Effective mechanical properties defined for as-built material based on simple geometrical measures.
Grain boundaries typically dominate fracture toughness, strength and slow crack growth in ceramics. To improve these properties through mechanistically informed grain boundary engineering, precise ...measurement of the mechanical properties of individual boundaries is essential, although it is rarely achieved due to the complexity of the task. Here we present an approach to characterize fracture energy at the lengthscale of individual grain boundaries and demonstrate this capability with measurement of the surface energy of silicon carbide single crystals. We perform experiments using an in situ scanning electron microscopy-based double cantilever beam test, thus enabling viewing and measurement of stable crack growth directly. These experiments correlate well with our density functional theory calculations of the surface energy of the same silicon carbide plane. Subsequently, we measure the fracture energy for a bi-crystal of silicon carbide, diffusion bonded with a thin glassy layer.To improve mechanical properties in ceramics through grain boundary engineering, precise mechanical characterization of individual boundaries is vital yet difficult to achieve. Here authors perform experiments using an in situ scanning electron microscopy based double cantilever beam test, allowing to directly view and measure stable crack growth in silicon carbide.
We report that the shape, orientation, edge geometry, and thickness of chemical vapor deposition graphene domains can be controlled by the crystallographic orientations of Cu substrates. Under ...low-pressure conditions, single-layer graphene domains align with zigzag edges parallel to a single ⟨101⟩ direction on Cu(111) and Cu(101), while bilayer domains align to two directions on Cu(001). Under atmospheric pressure conditions, hexagonal domains also preferentially align. This discovery can be exploited to generate high-quality, tailored graphene with controlled domain thickness, orientations, edge geometries, and grain boundaries.
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