Surface-controlled dislocation multiplication in metal micropillars.
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.
Weinberger
Christopher R
CR
Department of Mechanical Engineering, Stanford University, Stanford, CA 94305-4040, USA. cweinber@stanford.edu
Cai
Wei
W
Phys Rev Lett. 2008 Apr 18;100(15):155502
18518121
Phys Rev Lett. 2008 May 9;100(18):185503
18518390
Phys Rev Lett. 2002 May 20;88(20):206106
12005584
Science. 1964 Apr 3;144(3614):17-25
17729790
Science. 2005 Aug 12;309(5737):1059-62
16099981
Phys Rev Lett. 2005 Mar 11;94(9):095501
15783975
Nat Mater. 2008 Feb;7(2):115-9
18157134
Science. 2004 Aug 13;305(5686):986-9
15310897
Nat Mater. 2004 Mar;3(3):158-63
14991017