Dislocations in Grain Boundary Regions: The Origin of Heterogeneous Microstrains in Nanocrystalline Materials

Zhenbo Zhang, Éva Ódor, Diana Farkas, Bertalan Jóni, Gábor Ribárik, Géza Tichy, Sree Harsha Nandam, Julia Ivanisenko, Michael Preuss, Tamás Ungár

Research output: Contribution to journalArticle

Abstract

Nanocrystalline materials reveal excellent mechanical properties but the mechanism by which they deform is still debated. X-ray line broadening indicates the presence of large heterogeneous strains even when the average grain size is smaller than 10 nm. Although the primary sources of heterogeneous strains are dislocations, their direct observation in nanocrystalline materials is challenging. In order to identify the source of heterogeneous strains in nanocrystalline materials, we prepared Pd-10 pct Au specimens by inert gas condensation and applied high-pressure torsion (HPT) up to γ ≅ 21. High-resolution transmission electron microscopy (HRTEM) and molecular dynamic (MD) simulations are used to investigate the dislocation structure in the grain interiors and in the grain boundary (GB) regions in the as-prepared and HPT-deformed specimens. Our results show that most of the GBs contain lattice dislocations with high densities. The average dislocation densities determined by HRTEM and MD simulation are in good correlation with the values provided by X-ray line profile analysis. Strain distribution determined by MD simulation is shown to follow the Krivoglaz–Wilkens strain function of dislocations. Experiments, MD simulations, and theoretical analysis all prove that the sources of strain broadening in X-ray diffraction of nanocrystalline materials are lattice dislocations in the GB region. The results are discussed in terms of misfit dislocations emanating in the GB regions reducing elastic strain compatibility. The results provide fundamental new insight for understanding the role of GBs in plastic deformation in both nanograin and coarse grain materials of any grain size.

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Nanocrystalline materials
Dislocations (crystals)
nanocrystals
Grain boundaries
grain boundaries
Molecular dynamics
molecular dynamics
Computer simulation
High resolution transmission electron microscopy
Torsional stress
torsion
simulation
grain size
Noble Gases
X rays
transmission electron microscopy
x rays
strain distribution
high resolution
Inert gases

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys

Cite this

Dislocations in Grain Boundary Regions : The Origin of Heterogeneous Microstrains in Nanocrystalline Materials. / Zhang, Zhenbo; Ódor, Éva; Farkas, Diana; Jóni, Bertalan; Ribárik, Gábor; Tichy, Géza; Nandam, Sree Harsha; Ivanisenko, Julia; Preuss, Michael; Ungár, Tamás.

In: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 01.01.2019.

Research output: Contribution to journalArticle

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AU - Jóni, Bertalan

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AU - Tichy, Géza

AU - Nandam, Sree Harsha

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