We provide a brief overview of theoretical models that address twinning and
detwinning processes in nanocrystalline and ultrafine-grained metals. In particular, we discuss
and compare special mechanisms for formation of nanoscale deformation twins at grain
boundaries (GBs) in nanocrystalline and ultrafine-grained materials. The twinning
mechanisms represent (i) the successive events of partial dislocation emission from GBs; (ii)
the cooperative emission of partial dislocations from GBs; and (iii) the multiplane nanoscale
shear generated at GBs. In addition, we examine the detwinning mechanism in ultrafinegrained
nanotwinned metals through stress-driven migration of incoherent boundaries of
nanoscale twins. We demonstrate that detwinning of ultrathin twins can occur at very low
stresses, while detwinning of thicker twins requires high applied stresses, and these
theoretically revealed conclusions are well consistent with recent experimental data.
Keywords: ultrafine-grained metals; plastic deformation; nanotwinned metals; twinning; detwinning; defects; modeling.
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