Influence of sample size, strain rate and temperature on deformation of an Fe-2.4 wt.% Si Bi-crystal and its paired single crystals

Grain boundaries play an important role in determining mechanical properties of materials. To investigate the behavior of a single grain boundary, micropillar compression on bi-crystals has been widely applied, which however, mainly focuses on face-centered cubic metals. In this work, we investigate the influence of micropillar size, strain rate and temperature on deformation behavior of an Fe-2.4 wt.% Si bi-crystal with a high angle grain boundary and its paired single crystals. Tests were carried out at room temperature and -80 ◦C, nominal micropillar sizes were 1 μm, 2 μm and 4 μm, while strain rates were 0.001 s$^{-1}$, 0.01 s $^{-1}$ and 0.1 s$^{-1}$. Slip trace analysis reveals slip transmission across the grain boundary in bi-crystalline pillars. The transmitted slip systems can be different from those activated in single crystals depending on orientation. The identified transmission pair has a high transmission factor and is insensitive to strain rate and temperature, but dependent on pillar size. In contrast, the difference in yield strength between bi-crystals and single crystals is more closely related to testing parameters. ... mehrFor single crystals, smaller pillars can activate slip systems with a lower Schmid factor and slip traces
become wavy due to cross-slip at a sub-ambient temperature.