Influence of a reduced mobility of triple points on grain growth in two dimensions

A vertex dynamics model is applied to the two-dimensional simulation of grain growth including a limited mobility of triple points. It is shown that a recent experiment on a triple node is well reproduced by the proposed model. This model is then applied to the grain growth of polycrystals to investigate the possible consequences of a reduced mobility of triple nodes. It is shown how this effect can be detected through a careful examination of the grain growth kinetics and grain size distribution function.     

Combined experimental and numerical study on the effective grain growth dynamics in highly anisotropic systems: Application to barium titanate

Abnormal grain growth is a commonly observed phenomenon in barium titanate. It is usually associated with grain boundaries of different mobility and energy present in the microstructure. The influence of interfaces with variable mobility and energy on grain growth is investigated by a combined experimental and numerical approach in a transition region where growth behaviour strongly deviates from Arrhenius behaviour. Abnormal growth occurs between 1275 and 1325 °C, with normal grain growth occurring above and below this temperature range. The overall grain growth rate of the small matrix grains in the transition region is found to increase nonlinearly with inverse temperature between the high- and low-temperature states. A similar behaviour is found in simulations using a 3-D mesoscale grain growth model under the assumption of fractions of grain boundaries being in the high- or low-temperature state. The transition at the grain boundary is in agreement with the complexion model. Additionally, the simulation is used to map the nucleation probability for abnormal grains in the transition region as a function of combined energy and mobility advantages. The energy advantage of the grain boundaries is found to be of greater importance for the nucleation of abnormal grains compared to results from mean field models.     

Dislocation–grain boundary interaction in 〈1 1 1〉 textured thin metal films

The interaction of lattice dislocations with symmetrical and asymmetrical tilt grain boundaries in 〈1 1 1〉 textured thin nickel films was investigated using atomistic simulation methods. It was found that the misorientation angle of the grain boundary, the sign of the Burgers vector of the incoming dislocation and the exact site where the dislocation meets the grain boundary are all important parameters determining the ability of the dislocation to penetrate the boundary. Inclination angle, however, does not make an important difference on the transmission scenario of full dislocations. Only limited partial dislocation nucleation was observed for the investigated high-angle grain boundary. The peculiarities of nucleation of embryonic dislocations and their emission from tilt grain boundaries are discussed.     

Dislocation junctions as indicators of elementary slip planes in body-centered cubic metals

In body-centered cubic (bcc) metals, an unambiguous determination of the elementary slip planes remains difficult owing to several possible interpretations of the glide activity, of slip steps on the specimen surface or features of the dislocation microstructure. In this article, a method is proposed to determine the elementary slip planes in bcc metals based on the line directions of sessile junctions resulting from the interaction of mobile dislocations with \({a}/2\langle 111\rangle \)  Burgers vector. The proposed method allows to determine slip activity inside a material and not at its surface, where other effects may play a role. It is in principle applicable to determining the elementary slip plane in any crystalline material. Particularly, it may help to resolve a long-standing debate of the nature of the elementary slip planes in bcc metals.     

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Initial dislocation structures in 3-D discrete dislocation dynamics and their influence on microscale plasticity

Realistic dislocation network topologies were generated by relaxing an initially pinning point free dislocation loop structure using three-dimensional discrete dislocation dynamics simulations. Traction-free finite-sized samples were used. Subsequently, these equilibrated structures were subjected to tensile loading and their mechanical behavior was investigated with respect to the initial configuration. A strong mechanical size effect was found. The flow stress at 0.2% plastic deformation scales with specimen size with an exponent between ?0.6 and ?0.9, depending on the initial structure and size regime. During relaxation, a mechanism, also favored by cross-slip, is identified which leads to rather stable pinning points. These pinning points are comparable to those of the isolated Frank–Read sources often used as a starting configuration in previous discrete dislocation dynamics simulations. These nodes act as quite stable dislocation sources, which can be activated multiple times. The influence of this source mechanism on the mechanical properties of small-scale specimens is discussed.