Incompatibility stresses at grain boundaries in Ni bicrystalline micropillars analyzed by an anisotropic model and slip activity

Abstract

Incompatibility stresses can develop in bicrystals due to material elastic and plastic anisotropies owing to different crystal orientations separated by grain boundaries. Here, these stresses are investigated by combining experimental and theoretical studies on 10 lm diameter Ni bicrystalline micropillars. Throughout stepwise compression tests, slip traces are analyzed by scanning electron microscopy to identify the active slip planes and directions in both crystals. An analytical model is presented accounting for the effects of heterogeneous elasticity coupled to heterogeneous plasticity on the internal mechanical fields. This model provides explicit expressions of stresses in both crystals considering experimentally observed nonequal crystal volume fractions and inclined grain boundaries. It is used to predict the resolved shear stresses on the possible slip systems in each crystal. The predictions of the onset of plasticity as given by the present model in pure elasticity are compared with those given by the classical Schmid's law. In contrast with Schmid's law, the predictions of the analytical model are in full agreement with the experimental observations regarding the most highly stressed crystal and active slip systems. The effects of plastic incompatibilities are also considered in addition to the elastic ones throughout the model. The analysis shows that elastic/plastic coupling incompatibilities together with different crystal volume fractions have significant effects on the slip system activation process.

The mechanism of twinning activation and variant selection in magnesium alloys dominated by slip deformation

“…However, it should be addressed that the absence of slip bands in M d (see Fig. 8a) does not necessarily mean that basal slip is not activated because the SF for basal slip is high and the appearance of slip bands is dependent on crystal orientations and the plane viewed [31]. Another interesting point is that slip bands were also observed in the twins, T d .…”

Influence of inclined twin boundaries on the deformation behavior of Cu micropillars

“…A factor that has to be taken into consideration, however, is Young's modulus of both grains. Depending on the inclination of the boundary, the influence of elastic anisotropy will increase until reaching a maximum when the boundary is parallel to the compression direction [37]. A large difference in elastic properties leads to higher stresses in the stiffer grain and therefore facilitates dislocation source activation in this grain until plastification (depending on available slip systems and their Schmid factors).…”

Elastic fields due to dislocations in anisotropic bi- and tri-materials: Applications to discrete dislocation pile-ups at grain boundaries

“…It should be pointed out that in the present work, the introduction of the homogenous stress tensor has only for objective to equilibrate the dislocation pile-up. Even in the absence of singularities like dislocations, an infinite heterogeneously elastic material that is submitted to some (remotely) applied stress will actually display stress heterogeneities due to incompatibility stresses that are needed to maintain the continuity conditions at the interfaces (Gemperlová et al, 1989;Richeton and Berbenni, 2013;Tiba et al, 2015). In this paper, these long-range incompatibility stresses due to heterogeneous anisotropic elasticity are neglected since only the normal 22-component of is non-zero.…”