We present a stability map which predicts the domains of shear instability due to grain rotation in nanocrystalline materials. The onset of this mode of instability is influenced by grain-size-dependent mechanisms and the length-scale of intergranular interaction. The map shows the grain size regimes that are inherently susceptible to this mode for a range of materials. In the amorphous limit, the model predicts embryonic nuclei sizes of about 10–50 nm, which agrees well with the shear band thicknesses for many metallic glasses.

• Received 28 March 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.025501