On shear-coupled migration of grain boundaries in nanocrystalline materials

2012 ◽  
Vol 101 (24) ◽  
pp. 241915 ◽  
Author(s):  
Jianjun Li ◽  
A. K. Soh
Keyword(s):  
Grain Boundaries ◽  
Nanocrystalline Materials

Deformation Twins Formed in Nanocrystalline Materials

2006 ◽  
Vol 503-504 ◽  
pp. 125-132 ◽  
Author(s):  
Yuntian T. Zhu
Keyword(s):  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Partial Dislocation ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Nucleation And Growth ◽  
Analytical Models ◽  
Partial Dislocations ◽  
Deformation Twins ◽  
Low Strain Rate

Deformation twins have been oberved in nanocrystalline (NC) Al synthsized by cryogenic ball-milling and in NC Cu processed by high-pressure torsion under room temperature and at a very low strain rate. They were found formed by partial dislocations emitted from grain boundaries. This paper first reviews experimental evidences on deformation twinning and partial dislocation emissions from grain boundaries, and then discusses recent analytical models on the nucleation and growth of deformation twins. These models are compared with experimental results to establish their validity and limitations.

What is Behind the Inverse Hall-Petch Behavior in Nanocrystalline Materials?

2006 ◽  
Vol 976 ◽  
Author(s):  
Christopher Carlton ◽  
P. J. Ferreira
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Critical Value ◽  
Petch Relationship ◽  
And Diffusion ◽  
Critical Grain Size

AbstractAn inverse Hall-Petch effect has been observed for nanocrystalline materials by a large number of researchers. This result implies that nanocrystalline materials get softer as grain size is reduced below a critical value. Postulated explanations for this behavior include dislocation based mechanisms and diffusion based mechanisms. In this paper, we report an explanation for the inverse Hall-Petch effect based on the statistical absorption of dislocations by grain boundaries, showing that the yield strength is both dependent on strain rate and temperature, and that it deviates from the Hall-Petch relationship at a critical grain size.

Self-Diffusion Parameters of Grain Boundaries and Triple Junctions in Nanocrystalline Materials

2011 ◽  
Vol 309-310 ◽  
pp. 45-50 ◽  
Author(s):  
Aleksey Lipnitskii ◽  
I.V. Nelasov ◽  
Yurii Kolobov
Keyword(s):  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Boundary Diffusion ◽  
Coarse Grained ◽  
Triple Junctions ◽  
Dynamic Simulations ◽  
Self Diffusion ◽  
Diffusion Parameters ◽  
Diffusion Characteristics ◽  
First Time

Suggested methods describe the process of self-diffusion along grain boundaries and triple junctions in polycrystals without using geometric models of the grain boundaries structure. The calculation method introduced diffusion characteristics along grain boundaries derived from the results of molecular dynamic simulations of nanocrystalline materials. The diffusion experiments were imposed to establish relationship between introduced diffusion characteristics and the diffusion parameters along grain boundaries and triple junctions of the Fisher’s grain boundary diffusion model. By the example of copper for the first time the characteristics of self-diffusion along grain boundaries of nanocrystalline materials and coarse grained analog defined in the same temperature range was compared for the first time. It was found that values of the self-diffusion characteristics along grain boundaries in high purity nanocrystalline and polycrystalline copper are equal at the same temperatures.

Transformations of grain boundaries in deformed nanocrystalline materials

2004 ◽  
Vol 52 (13) ◽  
pp. 3793-3805 ◽  
Author(s):  
S.V Bobylev ◽  
M.Yu Gutkin ◽  
I.A Ovid'ko
Keyword(s):  
Grain Boundaries ◽  
Nanocrystalline Materials

Near-Equilibrium Solubility of Nanocrystalline Alloys

2012 ◽  
Vol 1371 ◽  
Author(s):  
Alexander Kirchner ◽  
Thomas Riedl ◽  
Konrad Eymann ◽  
Michael Noethe ◽  
Bernd Kieback
Keyword(s):  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Excess Volume ◽  
Boundary Segregation ◽  
Equilibrium Solubility ◽  
Equilibrium Conditions ◽  
Common System ◽  
Proposed Model ◽  
Materials Behavior ◽  
Atomistic Computer Simulation

ABSTRACTGrain boundaries are the dominating type of defect in nanocrystalline materials. Understanding their properties is crucial to the comprehension of nanocrystalline materials behavior. A facile thermodynamic model for alloy grain boundaries is developed. The macroscopic analysis is based on established descriptions of metallic solutions and the universal equation of state at negative pressure, using mainly parameters obtainable from measurements on macroscopic samples. The free energy of atoms in grain boundaries is derived as a function of excess volume, composition, and temperature. Interfacial enrichment is computed using equilibrium conditions between bulk phase and grain boundaries. The excess volume of symmetric ‘100’ tilt grain boundaries in Cu as a common system is obtained by atomistic computer simulation. In a general case the predictions of the proposed model are compared to experimental grain boundary segregation data, yielding a good match. The near-equilibrium solubility of Ag in nanocrystalline Cu and of Cu in nanocrystalline Fe is calculated.

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