title: Linking stress-driven microstructural evolution in nanocrystalline aluminium with grain boundary doping of oxygen.
abstract: The large fraction of material residing at grain boundaries in nanocrystalline metals and alloys is responsible for their ultrahigh strength, but also undesirable microstructural instability under thermal and mechanical loads. However, the underlying mechanism of stress-driven microstructural evolution is still poorly understood and precludes rational alloy design. Here we combine quantitative in situ electron microscopy with three-dimensional atom-probe tomography to directly link the mechanics and kinetics of grain boundary migration in nanocrystalline Al films with the excess of O atoms at the boundaries. Site-specific nanoindentation leads to grain growth that is retarded by impurities, and enables quantification of the critical stress for the onset of grain boundary migration. Our results show that a critical excess of impurities is required to stabilize interfaces in nanocrystalline materials against mechanical driving forces, providing new insights to guide control of deformation mechanisms and tailoring of mechanical properties apart from grain size alone.
authors.affiliation: Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Mo-Rigen
authors.initials: MR
authors.lastname: He
authors.affiliation: Australian Centre for Microscopy and Microanalysis, School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: Saritha K
authors.initials: SK
authors.lastname: Samudrala
authors.affiliation: Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Gyuseok
authors.initials: G
authors.lastname: Kim
authors.affiliation: Australian Centre for Microscopy and Microanalysis, School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Felfer
authors.affiliation: Australian Centre for Microscopy and Microanalysis, School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Breen
authors.affiliation: Australian Centre for Microscopy and Microanalysis, School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: Julie M
authors.initials: JM
authors.lastname: Cairney
authors.affiliation: Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.|Department of Materials, University of California Santa Barbara, Santa Barbara, California 93106, USA.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Gianola