title: The critical role of grain orientation and applied stress in nanoscale twinning.
abstract: Numerous recent studies have focused on the effects of grain size on deformation twinning in nanocrystalline fcc metals. However, grain size alone cannot explain many observed twinning characteristics. Here we show that the propensity for twinning is dependent on the applied stress, grain orientation and stacking fault energy. The lone factor for twinning dependent on grain size is the stress necessary to nucleate partial dislocations from a boundary. We use bulk processing of controlled nanostructures coupled with unique orientation mapping at the nanoscale to show the profound effect of crystal orientation on deformation twinning. Our theoretical model reveals an orientation-dependent critical threshold stress for twinning, which is presented in the form of a generalized twinnability map. Our findings provide a newfound orientation-based explanation for the grain size effect: as grain size decreases the applied stress needed for further deformation increases, thereby allowing more orientations to reach the threshold stress for twinning.
authors.affiliation: Materials Science and Technology Division, MST-6: materials technology-metallurgy, Los Alamos, New Mexico 87545, USA.
authors.forename: Rodney J
authors.initials: RJ
authors.lastname: McCabe
authors.affiliation: Theoretical Division, T-3: fluid dynamics and solid mechanics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: Irene J
authors.initials: IJ
authors.lastname: Beyerlein
authors.affiliation: Materials Science and Technology Division, MST-6: materials technology-metallurgy, Los Alamos, New Mexico 87545, USA.
authors.forename: John S
authors.initials: JS
authors.lastname: Carpenter
authors.affiliation: 1] Materials Science and Technology Division, MST-6: materials technology-metallurgy, Los Alamos, New Mexico 87545, USA [2] Materials Physics and Applications Division, MPA-CINT: Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: Nathan A
authors.initials: NA
authors.lastname: Mara