Journal ArticleDOI
Grain boundary-mediated plasticity in nanocrystalline nickel.
Zhi-Wei Shan,Eric A. Stach,Jörg M.K. Wiezorek,James Arthur Knapp,David M. Follstaedt,Scott X. Mao +5 more
TLDR
Observations of nanocrystalline nickel films with an average grain size of about 10 nanometers show that grain boundary–mediated processes have become a prominent deformation mode, and trapped lattice dislocations are observed in individual grains following deformation.Abstract:
The plastic behavior of crystalline materials is mainly controlled by the nucleation and motion of lattice dislocations. We report in situ dynamic transmission electron microscope observations of nanocrystalline nickel films with an average grain size of about 10 nanometers, which show that grain boundary-mediated processes have become a prominent deformation mode. Additionally, trapped lattice dislocations are observed in individual grains following deformation. This change in the deformation mode arises from the grain size-dependent competition between the deformation controlled by nucleation and motion of dislocations and the deformation controlled by diffusion-assisted grain boundary processes.read more
Citations
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Journal ArticleDOI
Deformation twinning in nanocrystalline materials
TL;DR: In this paper, a review of deformation twinning in nanocrystalline materials is presented, including deformation twins observed by molecular dynamics simulations and experiments, twinning mechanisms, factors affecting the twinning, analytical models on the nucleation and growth of deformations, interactions between twins and dislocations, and the effects of twins on mechanical and other properties.
Journal ArticleDOI
Toward a quantitative understanding of mechanical behavior of nanocrystalline metals
TL;DR: A brief overview of the recent progress made in improving mechanical properties of nanocrystalline materials, and in quantitatively and mechanistically understanding the underlying mechanisms is presented in this paper.
Journal ArticleDOI
Dislocation nucleation governed softening and maximum strength in nano-twinned metals
TL;DR: It is shown that dislocation nucleation governs the strength of nano-twinned materials, resulting in their softening below a critical twin thickness, and the critical twin-boundary spacing and the maximum strength depend on the grain size.
Journal ArticleDOI
Coupling grain boundary motion to shear deformation
TL;DR: In this paper, the coupling factor between the normal grain boundary (GB) motion and grain translations has been calculated by molecular dynamics simulations over the entire misorientation range and a wide range of temperatures, showing an abrupt switch from one branch to another at a tilt angle of about 35°.
Journal ArticleDOI
Nano-sized twins induce high rate sensitivity of flow stress in pure copper
TL;DR: In this article, the authors investigated the rate sensitivity of flow stress and the extent of strengthening in polycrystalline copper containing different volume fractions of nano-sized twins, but having the same average grain size.
References
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Book
Theory of Dislocations
John Price Hirth,Jens Lothe +1 more
TL;DR: Dislocations in Isotropic Continua: Effects of Crystal Structure on Dislocations and Dislocation-Point-Defect Interactions at Finite temperatures.
Journal ArticleDOI
Softening of nanocrystalline metals at very small grain sizes
TL;DR: In this paper, the deformation of nanocrystalline copper has been studied and it is shown that the hardness and yield stress of the material typically increase with decreasing grain size, a phenomenon known as the reverse Hall-Petch effect.
Journal ArticleDOI
A Maximum in the Strength of Nanocrystalline Copper
TL;DR: Using molecular dynamics simulations with system sizes up to 100 million atoms to simulate plastic deformation of nanocrystalline copper, it is shown that the flow stress and thus the strength exhibit a maximum at a grain size of 10 to 15 nanometers.
Journal ArticleDOI
On grain boundary sliding and diffusional creep
Rishi Raj,M.F. Ashby +1 more
TL;DR: In this paper, the problem of sliding at a nonplanar grain boundary is considered in detail, and the results give solutions to the following problems: 1) How much sliding occurs in a polycrystal when neither diffusive flow nor dislocation motion is possible? 2) What is the sliding rate at a wavy or stepped grain boundary when diffusional flow of matter occurs? 3) How is the rate of diffusional creep in polycrystals in which grain boundaries slide? 4) how is this creep rate affected by grain shape, and grain boundary migration? 5)