  Plasticity in body-centred cubic (BCC) metals, including dislocation
interactions at grain boundaries, is much less understood than in face-centred
cubic (FCC) metals. At low temperatures additional resistance to dislocation
motion due to the Peierls barrier becomes important, which increases the
complexity of plasticity. Iron-silicon steel is an interesting, model BCC
material since the evolution of the dislocation structure in
specifically-oriented grains and at particular grain boundaries have
far-reaching effects not only on the deformation behaviour but also on the
magnetic properties, which are important in its final application as electrical
steel. In this study, two different orientations of micropillars (1, 2, 4
microns in diameter) and macropillars (2500 microns) and their corresponding bi
crystals are analysed after compression experiments with respect to the effect
of size on strength and dislocation structures. Using different experimental
methods, such as slip trace analysis, plane tilt analysis and cross-sectional
EBSD, we show that direct slip transmission occurs, and different slip systems
are active in the bi-crystals compared to their single-crystal counterparts.
However, in spite of direct transmission and a very high transmission factor,
dislocation pile-up at the grain boundary is also observed at early stages of
deformation. Moreover, an effect of size scaling with the pillar size in single
crystals and the grain size in bi-crystals is found, which is consistent with
investigations elsewhere in FCC metals.
