title: Planar defect nucleation and annihilation mechanisms in nanocontact plasticity of metal surfaces.
abstract: The incipient contact plasticity of metallic surfaces involves nucleation of crystalline defects. The present molecular dynamics simulations and nanoindentation experiments demonstrate that the current notion of nanocontact plasticity in fcc metals does not apply to high-strength bcc metals. We show that nanocontact plasticity in Ta-a model bcc metal-is triggered by thermal and loading-rate dependent (dynamic) nucleation of planar defects such as twins and unique {011} stacking fault bands. Nucleation of different planar defects depending on surface orientation leads to distinct signatures (pop ins) in the nanoindentation curves. Nanoscale plasticity is then ruled by an outstanding dynamical mechanism governing twin annihilation and subsequent emission of linear defects (full dislocations). While this investigation concerns Ta crystals, the present are landmark findings for other model bcc metals.
authors.affiliation: Department of Materials Science and Metallurgical Engineering, GRICCA, EUETIB and ETSEIB, Universitat Politècnica de Catalunya, Barcelona, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Alcalá
authors.forename: Roger
authors.initials: R
authors.lastname: Dalmau
authors.forename: Oliver
authors.initials: O
authors.lastname: Franke
authors.forename: Monika
authors.initials: M
authors.lastname: Biener
authors.forename: Juergen
authors.initials: J
authors.lastname: Biener
authors.forename: Andrea
authors.initials: A
authors.lastname: Hodge