Fracture Energy Measurement of Prismatic Plane and Σ2 Boundary in Cemented Carbide

The grain boundary network of WC in WC-Co is important, as cracks often travel intergranularly. This motivates the present work, where we experimentally measure the fracture energy of Σ2 twist grain boundaries between WC crystals using a double cantilever beam opened with a wedge under displacement control in a WC-10wt%Co sample. The fracture energy of this boundary type was compared with cleaving {$$10\overline{1}0$$ 10 1 ¯ 0 } prismatic planes in a WC single crystal. Fracture energies of 7.04 ± 0.36 Jm−2 and 3.57 ± 0.28 Jm−2 were measured for {$$10\overline{1}0$$ 10 1 ¯ 0 } plane and Σ2 twist boundaries, respectively.

Role of point defects in self-diffusion along low-angle twist boundaries in fcc metals: A molecular dynamics study

The interaction of point defects with low-angle (100), (110) and (111) twist boundaries in fcc metals Ni, Cu, Al and role of the point defects in self-diffusion along considered boundaries were studied by the molecular dynamics method. The binding energies of point defects with low-angle twist boundaries were calculated. It was found that the point defects are mainly fixed in the nodes of grain-boundary screw dislocations network. It was shown that the introduced vacancies play an important role in diffusion along twist grain boundaries. The contribution of introduced interstitial atoms to grain-boundary diffusion under thermodynamic equilibrium condition is less by several orders of magnitude in comparison with the contribution of vacancies.

Effect of Grain Boundary Geometry on Grain Rotation during Curvature-Driven Grain Shrinkage

Molecular dynamics simulations were performed to analyze the curvature-driven shrinkage of individual cylindrical grains with geometrically different boundaries in Al. Grains with <100> tilt and mixed tilt-twist boundaries with the misorientations 5.5°, 16.3°, and 22.6° were simulated. The results revealed that the shrinking grains with tilt boundaries concurrently rotate increasing the misorientation angles, whereas grains with the mixed boundaries did not rotate during their shrinkage. Apparently, the grain boundary geometry/structure has a crucial impact on the observed rotational behavior of the computed grains. The grains with tilt boundaries rotate due to the lack of effectively operating mechanisms for annihilation of edge dislocations, which compose such boundaries. In contrast, for the mixed boundaries composed of edge-screw dislocations the sufficiently fast operating mechanisms of dislocation elimination are available, which facilitates grain shrinkage without rotation.

Motion of Grain Boundaries: Experiments on Bicrystals

Recent research on grain boundary migration is reviewed. Novel in-situ measuring techniques based on orientation contrast imaging and the experimental results obtained on specially grown bicrystals are presented. Particularly, the investigated faceting and migration behavior of low angle grain boundaries under the curvature force in aluminum bicrystals was addressed. In contrast to the pure tilt boundaries, which remained straight/flat and immobile during annealing at elevated temperatures, mixed tilt-twist boundaries readily assumed a curved shape and steadily moved under the capillary force. Computational analysis revealed that this behavior is due to the inclinational anisotropy of grain boundary energy, which in turn depends on boundary geometry. The migration of planar grain boundaries induced by a magnetic field was measured in bismuth and zinc bicrystals. Various structurally different boundaries were investigated. The results revealed that grain boundary mobility essentially depends on the misorientation angle and the inclination of the boundary plane. Stress driven boundary migration in aluminium bicrystals was observed to be coupled to a tangential translation of the grains. The activation enthalpy of high angle boundary migration was found to vary non-monotonously with misorientation angle, whereas for low angle boundaries the migration activation enthalpy was virtually the same. The motion of the mixed tilt-twist boundaries under stress was observed to be accompanied by both the translation of adjacent grains parallel to the boundary plane and their rotation around the boundary plane normal.

Effect of Grain Boundary Energy Anisotropy on Faceting and Migration of Low Angle Grain Boundaries

The faceting and migration behavior of low angle <100> grain boundaries in high purity aluminum bicrystals was investigated. In-situ technique based on orientation contrast imaging was applied. In contrast to the pure tilt boundaries, which remained straight/flat and immobile during annealing at elevated temperatures, mixed tilt-twist boundaries readily assumed a curved shape and steadily moved under the capillary force. Computational analysis revealed that this behavior is due to the inclinational anisotropy of grain boundary energy, which in turn depends on boundary geometry – the energy of pure tilt low angle <100> boundaries is anisotropic, whereas that of mixed tilt-twist boundaries isotropic with respect to boundary inclination.