Abstract
Compression tests at low strains were performed to theoretically analyze the effects of anisotropic elasticity, misorientation, grain boundary (GB) stiffness, interfacial dislocations, free surfaces, and critical force on dislocation pile-ups in micro-sized Face-Centered Cubic (FCC) Nickel (Ni) and α -Brass bi-crystals. The spatial variations of slip heights due to localized slip bands terminating at GB were measured by Atomic Force Microscopy (AFM) to determine the Burgers vector distributions in the dislocation pile-ups. These distributions were then simulated by discrete pile-up micromechanical calculations in anisotropic bi-crystals consistent with the experimentally measured material parameters. The computations were based on the image decomposition method considering the effects of interphase GB and free surfaces in multilayered materials. For Ni and α -Brass, it was found that the best predicted step height spatial profiles were obtained considering anisotropic elasticity, free surface effects, a homogeneous external stress and a certain critical force in the material to equilibrate the dislocation pile-ups.
Highlights
The plasticity of crystalline materials results primarily from motion and multiplication of dislocations
The results include the Schmid factors, the resolved shear stresses normalized by the applied stress considering elastic incompatibility stresses as detailed in [37,38], the angles between the slip line and the grain boundary (GB) line on the upper surface θUp, the angles between the slip line and the upper edge of sample on the side surface θSide and the maximum transmission factor with corresponding slip system in the adjacent grain
Experimental studies of Burgers vector distribution in discrete dislocation pile-ups at GB were performed in Ni and α-Brass bi-crystalline micro-pillars
Summary
The plasticity of crystalline materials results primarily from motion and multiplication of dislocations. Both theoretical and experimental investigations show that the mechanical properties of metals depend on the density, the distribution, the nucleation, and the mobility of dislocations. The mechanical properties of polycrystals depend on the presence of grain boundaries (GBs), such as the elastic limit and strain hardening. These properties are greatly dependent on the interaction mechanisms between dislocations and GBs (dislocation transmission or absorption at GB, formation of a dislocation pile-up, etc.). GBs generally present themselves as obstacles to dislocation motion. In the case of grain size reduction, which means the increase of GB fraction in the material, the material strength is increased following the Hall–Petch’s relationship [1,2,3]
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