Nanocrystalline materials were known to deform via mechanisms not accessible to their coarse-grained counterparts. For example, deformation twins and partial dislocations emitted from grain boundaries were observed in nanocrystalline Al and Cu synthesized by severe plastic deformation. This paper further develops an earlier dislocation-based model on the nucleation of deformation twins in nanocrystalline face-centered-cubic metals. It was found that there exists an optimum grain-size range in which deformation twins nucleate most readily. The critical twinning stress was found determined primarily by the stacking fault energy while the optimum grain size was largely determined by ratio of shear modulus to stacking fault energy. This model formulated herein was applicable to face-centred cubic nanomaterials synthesized by severe plastic deformation techniques and provide a lower bound to the critical twining stress.

Nucleation of Deformation Twins in Nanocrystalline Face-Centered-Cubic Metals Processed by Severe Plastic Deformation. Y.T.Zhu, X.Z.Liao, S.G.Srinivasan, E.J.Lavernia: Journal of Applied Physics, 2005, 98[3], 034319 (8pp)