Entropic effect on the rate of dislocation nucleation

Seunghwa Ryu, Keonwook Kang, Wei Cai

Research output: Contribution to journalArticle

83 Citations (Scopus)

Abstract

Dislocation nucleation is essential to our understanding of plastic deformation, ductility, and mechanical strength of crystalline materials. Molecular dynamics simulation has played an important role in uncovering the fundamental mechanisms of dislocation nucleation, but its limited timescale remains a significant challenge for studying nucleation at experimentally relevant conditions. Here we show that dislocation nucleation rates can be accurately predicted over a wide range of conditions by determining the activation free energy from umbrella sampling. Our data reveal very large activation entropies, which contribute a multiplicative factor of many orders of magnitude to the nucleation rate. The activation entropy at constant strain is caused by thermal expansion, with negligible contribution from the vibrational entropy. The activation entropy at constant stress is significantly larger than that at constant strain, as a result of thermal softening. The large activation entropies are caused by anharmonic effects, showing the limitations of the harmonic approximation widely used for rate estimation in solids. Similar behaviors are expected to occur in other nucleation processes in solids.

Original languageEnglish
Pages (from-to)5174-5178
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume108
Issue number13
DOIs
Publication statusPublished - 2011 Mar 29

All Science Journal Classification (ASJC) codes

  • General

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