Microscopic description of plasticity in computer generated metallic nanophase samples: A comparison between Cu and Ni

Simulations are reported on the plastic behavior of two model f.c.c. metals , Ni and Cu, with different stacking fault energies, and average grain size s in the range of 3-12 nm. A change in deformation mechanism is observed: a t the smallest grain sizes all deformation is accommodated in the grain bou ndaries. Al higher grain sizes intragrain deformation is observed. Analysis of the atomic configurations shows that intrinsic stacking faults are prod uced by motion of Shockley partial dislocations generated and absorbed in o pposite grain boundaries. In Cu the stacking faults are observed at smaller grain sizes than in Ni (8 nm in Cu, 12 nm in Ni) which is attributed to th e lower stacking fault energy. Shockley partial dislocations appear on slip systems that are not necessarily those favored by the Schmid factor. Atomi c displacement analysis shows that deformation starts at triple points, wit h grain boundary sliding followed by the creation of intragrain partial dis locations. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Lt d. All rights reserved.