Contrary to the common belief that many-fold twins in nanophase materials were due to the action of significant external stresses, molecular dynamics simulations of 5nm grain size Cu samples annealed at 800K revealed the formation of fivefold twins with no external pressure. The structure of the many-fold twins was remarkably similar to those found to occur under uniaxial shock loading in nanocrystalline NiW.

Fivefold Twin Formation During Annealing of Nanocrystalline Cu. E.M.Bringa, D.Farkas, A.Caro, Y.M.Wang, J.McNaney, R.Smith: Scripta Materialia, 2008, 59[12], 1267-70