title: Surface-controlled dislocation multiplication in metal micropillars.
abstract: Understanding the plasticity and strength of crystalline materials in terms of the dynamics of microscopic defects has been a goal of materials research in the last 70 years. The size-dependent yield stress observed in recent experiments of submicrometer metallic pillars provides a unique opportunity to test our theoretical models, allowing the predictions from defect dynamics simulations to be directly compared with mechanical strength measurements. Although depletion of dislocations from submicrometer face-centered-cubic (FCC) pillars provides a plausible explanation of the observed size-effect, we predict multiplication of dislocations in body-centered-cubic (BCC) pillars through a series of molecular dynamics and dislocation dynamics simulations. Under the combined effects from the image stress and dislocation core structure, a dislocation nucleated from the surface of a BCC pillar generates one or more dislocations moving in the opposite direction before it exits from the surface. The process is repeatable so that a single nucleation event is able to produce a much larger amount of plastic deformation than that in FCC pillars. This self-multiplication mechanism suggests a need for a different explanation of the size dependence of yield stress in FCC and BCC pillars.
authors.affiliation: Department of Mechanical Engineering, Stanford University, Stanford, CA 94305-4040, USA. cweinber@stanford.edu
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Weinberger
authors.forename: Wei
authors.initials: W
authors.lastname: Cai
references.citation: Phys Rev Lett. 2008 Apr 18;100(15):155502
references.pmid: 18518121
references.citation: Phys Rev Lett. 2008 May 9;100(18):185503
references.pmid: 18518390
references.citation: Phys Rev Lett. 2002 May 20;88(20):206106
references.pmid: 12005584
references.citation: Science. 1964 Apr 3;144(3614):17-25
references.pmid: 17729790
references.citation: Science. 2005 Aug 12;309(5737):1059-62
references.pmid: 16099981
references.citation: Phys Rev Lett. 2005 Mar 11;94(9):095501
references.pmid: 15783975
references.citation: Nat Mater. 2008 Feb;7(2):115-9
references.pmid: 18157134
references.citation: Science. 2004 Aug 13;305(5686):986-9
references.pmid: 15310897
references.citation: Nat Mater. 2004 Mar;3(3):158-63
references.pmid: 14991017