It was recalled that fivefold deformation twins had recently been observed in nanocrystalline face-centered cubic metals and alloys synthesized by severe plastic deformation. Numerous molecular dynamics simulations in the literature had failed to observe fivefold deformation twins in nanocrystalline face-centred cubic metals. The discrepancy between experimental observations and molecular dynamics simulations raised the issue of their formation mechanism and conditions. A sequential twinning mechanism was proposed here that provided a clear path for the formation of fivefold deformation twins. The mechanism required an orientation change of the applied stresses; which explained why molecular dynamics simulations under a constant-load orientation did not produce fivefold deformation twins.

Formation Mechanism of Fivefold Deformation Twins in Nanocrystalline Face-Centered-Cubic Metals. Y.T.Zhu, X.Z.Liao, R.Z.Valiev: Applied Physics Letters, 2005, 86[10], 103112 (3pp)