scholarly journals Twinning-assisted dynamic adjustment of grain boundary mobility

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Qishan Huang ◽  
Qi Zhu ◽  
Yingbin Chen ◽  
Mingyu Gong ◽  
Jixue Li ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Nanocrystalline Materials ◽  
High Performance ◽  
Practical Implication ◽  
Local Deformation ◽  
Dynamic Adjustment ◽  
Grain Boundary Mobility ◽  
Wide Range ◽  
Mechanical Behaviours ◽  
Dynamics Simulations

AbstractGrain boundary (GB) plasticity dominates the mechanical behaviours of nanocrystalline materials. Under mechanical loading, GB configuration and its local deformation geometry change dynamically with the deformation; the dynamic variation of GB deformability, however, remains largely elusive, especially regarding its relation with the frequently-observed GB-associated deformation twins in nanocrystalline materials. Attention here is focused on the GB dynamics in metallic nanocrystals, by means of well-designed in situ nanomechanical testing integrated with molecular dynamics simulations. GBs with low mobility are found to dynamically adjust their configurations and local deformation geometries via crystallographic twinning, which instantly changes the GB dynamics and enhances the GB mobility. This self-adjust twin-assisted GB dynamics is found common in a wide range of face-centred cubic nanocrystalline metals under different deformation conditions. These findings enrich our understanding of GB-mediated plasticity, especially the dynamic behaviour of GBs, and bear practical implication for developing high performance nanocrystalline materials through interface engineering.

Grain Growth Stagnation Caused by the Grain Boundary Roughening Transition

2012 ◽  
Vol 715-716 ◽  
pp. 415-415
Author(s):  
Elizabeth A. Holm ◽  
Stephen M. Foiles
Keyword(s):  
Molecular Dynamics ◽  
Transition Temperature ◽  
Grain Boundary ◽  
Molecular Dynamics Simulations ◽  
Grain Growth ◽  
Boundary Mobility ◽  
Grain Boundary Mobility ◽  
Annealing Temperatures ◽  
Roughening Transition ◽  
Dynamics Simulations

Molecular dynamics simulations of bicrystals show that grain boundaries undergo a thermal roughening transition, and the grain boundary mobility increases abruptly when the boundary roughens. The roughening transition temperature varies widely from boundary to boundary, ranging from less than 0.4 to more than 0.9 of the melting temperature. Thus, at typical annealing temperatures we expect polycrystals to contain both smooth (slow) and rough (fast) boundaries, with the fraction of each type varying with temperature.

scholarly journals A new approach to grain boundary engineering for nanocrystalline materials

2016 ◽  
Vol 7 ◽  
pp. 1829-1849 ◽  
Author(s):  
Shigeaki Kobayashi ◽  
Sadahiro Tsurekawa ◽  
Tadao Watanabe
Keyword(s):  
Grain Boundary ◽  
Fractal Analysis ◽  
Nanocrystalline Materials ◽  
High Performance ◽  
Functional Materials ◽  
Grain Boundary Character Distribution ◽  
Grain Boundary Engineering ◽  
Triple Junctions ◽  
New Approach ◽  
Boundary Connectivity

A new approach to grain boundary engineering (GBE) for high performance nanocrystalline materials, especially those produced by electrodeposition and sputtering, is discussed on the basis of some important findings from recently available results on GBE for nanocrystalline materials. In order to optimize their utility, the beneficial effects of grain boundary microstructures have been seriously considered according to the almost established approach to GBE. This approach has been increasingly recognized for the development of high performance nanocrystalline materials with an extremely high density of grain boundaries and triple junctions. The effectiveness of precisely controlled grain boundary microstructures (quantitatively characterized by the grain boundary character distribution (GBCD) and grain boundary connectivity associated with triple junctions) has been revealed for recent achievements in the enhancement of grain boundary strengthening, hardness, and the control of segregation-induced intergranular brittleness and intergranular fatigue fracture in electrodeposited nickel and nickel alloys with initial submicrometer-grained structure. A new approach to GBE based on fractal analysis of grain boundary connectivity is proposed to produce high performance nanocrystalline or submicrometer-grained materials with desirable mechanical properties such as enhanced fracture resistance. Finally, the potential power of GBE is demonstrated for high performance functional materials like gold thin films through precise control of electrical resistance based on the fractal analysis of the grain boundary microstructure.

Microstructural evolution during the heat treatment of nanocrystalline alloys

2007 ◽  
Vol 22 (11) ◽  
pp. 3233-3248 ◽  
Author(s):  
A.J. Detor ◽  
C.A. Schuh
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Microstructural Evolution ◽  
Nanocrystalline Materials ◽  
Boundary Segregation ◽  
Nanocrystalline Alloys ◽  
Analytical Models ◽  
Boundary Structure ◽  
Chemical Ordering ◽  
Wide Range

Nanocrystalline alloys often show exceptional thermal stability as a consequence of kinetic and thermodynamic impediments to grain growth. However, evaluating the various contributions to stability requires detailed investigation of the solute distribution, which is challenging within the fine structural-length-scales of nanocrystalline materials. In the present work, we use a variety of techniques to assess changes in the grain size, chemical ordering, grain-boundary segregation, and grain-boundary structure during the heat treatment of Ni–W specimens synthesized over a wide range of grain sizes from 3 to 70 nm. A schematic microstructural evolution map is also developed based on analytical models of the various processes activated during annealing, highlighting the effects of alloying in nanocrystalline materials.

Introducing Solute Drag in Irregular Cellular Automata Modeling of Grain Growth

2004 ◽  
Vol 467-470 ◽  
pp. 1045-1050 ◽  
Author(s):  
Koenraad G.F. Janssens ◽  
Elizabeth A. Holm ◽  
Stephen M. Foiles
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Boundary Energy ◽  
Solute Drag ◽  
Solute Concentration ◽  
Local Concentration ◽  
Boundary Mobility ◽  
Grain Boundary Mobility ◽  
Dynamics Simulations

In this paper we discuss the principles of a combined approach to solve the problem of solute drag as it occurs in microstructure evolution processes such as grain growth, recrystallization and phase transformation. A recently developed irregular grid cellular automaton is used to simulate normal grain growth, in which the energy of the grain boundaries is the driving force. A new, discrete diffusion model is used to simulate solute segregation to the grain boundaries. The local concentration of the solute is then taken into account in the calculation of the local grain boundary mobility and/or grain boundary energy, thereby constituting a drag force. The relation between solute concentration and grain boundary mobility/energy is derived from molecular dynamics simulations.

General Trend of Negative Transference Number in Li Salt/Ionic Liquid Mixtures

2019 ◽  
Author(s):  
Nicola Molinari ◽  
Jonathan P. Mailoa ◽  
Boris Kozinsky
Keyword(s):  
Ionic Liquid ◽  
Transference Number ◽  
Liquid Mixtures ◽  
Single Linkage ◽  
Self Diffusion ◽  
Wide Range ◽  
Single Linkage Cluster ◽  
Concentrated Solution ◽  
The One ◽  
Dynamics Simulations

We show that strong cation-anion interactions in a wide range of lithium-salt/ionic liquid mixtures result in a negative lithium transference number, using molecular dynamics simulations and rigorous concentrated solution theory. This behavior fundamentally deviates from the one obtained using self-diffusion coefficient analysis and agrees well with experimental electrophoretic NMR measurements, which accounts for ion correlations. We extend these findings to several ionic liquid compositions. We investigate the degree of spatial ionic coordination employing single-linkage cluster analysis, unveiling asymmetrical anion-cation clusters. Additionally, we formulate a way to compute the effective lithium charge that corresponds to and agrees well with electrophoretic measurements and show that lithium effectively carries a negative charge in a remarkably wide range of chemistries and concentrations. The generality of our observation has significant implications for the energy storage community, emphasizing the need to reconsider the potential of these systems as next generation battery electrolytes.<br>

Structure and properties of compact articles from high-alloyed iron powder with adding of boron nitride

2020 ◽  
pp. 39-48
Author(s):  
B. O. Bolshakov ◽  
◽  
R. F. Galiakbarov ◽  
A. M. Smyslov ◽  
◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Boron Nitride ◽  
Grain Boundary ◽  
Bending Strength ◽  
Physical And Mechanical Properties ◽  
Operating Conditions ◽  
Structure And Properties ◽  
Steam Turbines ◽  
Friction Forces ◽  
Wide Range

The results of the research of structure and properties of a composite compact from 13 Cr – 2 Мо and BN powders depending on the concentration of boron nitride are provided. It is shown that adding boron nitride in an amount of more than 2% by weight of the charge mixture leads to the formation of extended grain boundary porosity and finely dispersed BN layers in the structure, which provides a high level of wearing properties of the material. The effect of boron nitride concentration on physical and mechanical properties is determined. It was found that the introduction of a small amount of BN (up to 2 % by weight) into the compacts leads to an increase in plasticity, bending strength, and toughness by reducing the friction forces between the metal powder particles during pressing and a more complete grain boundary diffusion process during sintering. The formation of a regulated structure-phase composition of powder compacts of 13 Cr – 2 Mо – BN when the content of boron nitride changes in them allows us to provide the specified physical and mechanical properties in a wide range. The obtained results of studies of the physical and mechanical characteristics of the developed material allow us to reasonably choose the necessary composition of the powder compact for sealing structures of the flow part of steam turbines, depending on their operating conditions.

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