Predicting the dislocation nucleation rate as a function of temperature and stress

Seunghwa Ryu, Keon Wook Kang, Wei Cai

Research output: Contribution to journalArticle

34 Citations (Scopus)

Abstract

Predicting the dislocation nucleation rate as a function of temperature and stress is crucial for understanding the plastic deformation of nanoscale crystalline materials. However, the limited time scale of molecular dynamics simulations makes it very difficult to predict the dislocation nucleation rate at experimentally relevant conditions. We recently develop an approach to predict the dislocation nucleation rate based on the Becker-Döring theory of nucleation and umbrella sampling simulations. The results reveal very large activation entropies, which originated from the anharmonic effects, that can alter the nucleation rate by many orders of magnitude. Here we discuss the thermodynamics and algorithms underlying these calculations in greater detail. In particular, we prove that the activation Helmholtz free energy equals the activation Gibbs free energy in the thermodynamic limit and explain the large difference in the activation entropies in the constant stress and constant strain ensembles. We also discuss the origin of the large activation entropies for dislocation nucleation, along with previous theoretical estimates of the activation entropy.

Original languageEnglish
Pages (from-to)2335-2354
Number of pages20
JournalJournal of Materials Research
Volume26
Issue number18
DOIs
Publication statusPublished - 2011 Sep 28

Fingerprint

Nucleation
Chemical activation
nucleation
activation
Entropy
entropy
Temperature
temperature
Thermodynamics
thermodynamics
Gibbs free energy
Free energy
plastic deformation
Molecular dynamics
Plastic deformation
simulation
sampling
free energy
molecular dynamics
Sampling

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Cite this

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abstract = "Predicting the dislocation nucleation rate as a function of temperature and stress is crucial for understanding the plastic deformation of nanoscale crystalline materials. However, the limited time scale of molecular dynamics simulations makes it very difficult to predict the dislocation nucleation rate at experimentally relevant conditions. We recently develop an approach to predict the dislocation nucleation rate based on the Becker-D{\"o}ring theory of nucleation and umbrella sampling simulations. The results reveal very large activation entropies, which originated from the anharmonic effects, that can alter the nucleation rate by many orders of magnitude. Here we discuss the thermodynamics and algorithms underlying these calculations in greater detail. In particular, we prove that the activation Helmholtz free energy equals the activation Gibbs free energy in the thermodynamic limit and explain the large difference in the activation entropies in the constant stress and constant strain ensembles. We also discuss the origin of the large activation entropies for dislocation nucleation, along with previous theoretical estimates of the activation entropy.",
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Predicting the dislocation nucleation rate as a function of temperature and stress. / Ryu, Seunghwa; Kang, Keon Wook; Cai, Wei.

In: Journal of Materials Research, Vol. 26, No. 18, 28.09.2011, p. 2335-2354.

Research output: Contribution to journalArticle

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