Diffusion Impurity Drag of Twin Grain Boundaries and Triple Junctions Motion in Zinc

2005 ◽  
Vol 237-240 ◽  
pp. 578-583 ◽  
Author(s):  
Vera G. Sursaeva ◽  
Paweł Zięba
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Triple Junction ◽  
Experimental Results ◽  
Triple Junctions ◽  
Mechanical Twin ◽  
Adsorbed Atoms ◽  
Impurity Drag ◽  
Single Grain ◽  
First Time

The experimental results on motion of single grain boundaries (GBs) of natural mechanical twin and single fabricated twin GBs as well as on fabricated twin GBs in system with triple junction (TJ) are obtained. The mobility of natural mechanical twin GBs, fabricated single GBs and fabricated GBs with TJ are compared. For the first time the effect of detachment of moving TJ and single natural twin GB from adsorbed atoms is reported. The results on single GB migration are considered in context of triple junction migration as the step to grain growth, i.e. “polycrystal” experiments.

Triple Junction Controlled Grain Growth

2004 ◽  
Vol 467-470 ◽  
pp. 1093-1098 ◽  
Author(s):  
Vladimir Yu. Novikov
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Growth Kinetics ◽  
Triple Junction ◽  
Nanocrystalline Materials ◽  
Triple Junctions ◽  
Restricted Mobility ◽  
Triple Junction Mobility ◽  
Grain Diameter

Grain growth in 2D polycrystals was simulated under the supposition that triple junctions possess a restricted mobility and so impede the migration of grain boundaries. A parameter 0 L = 0 D m taking into account the effect of triple junctions was varied in the range from 0.003 to 270 (m is the ratio of the triple junction mobility to that of grain boundary and 0 D the initial grain diameter). It was shown that at 0 L <0.4–0.5, i.e. at a small 0 D and small m, the growth kinetics becomes linear. It is supposed that the effect of triple junctions on grain growth can be observed in nanocrystalline materials.

Thermodynamics and Kinetics of 1D Structural Elements and Stability of Nanocrystalline Materials

2015 ◽  
Vol 5 ◽  
pp. 173-195
Author(s):  
Günter Gottstein ◽  
Lazar S. Shvindlerman
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Triple Junction ◽  
Nanocrystalline Materials ◽  
Triple Line ◽  
Second Phase ◽  
Structural Elements ◽  
Triple Junctions ◽  
Line Energy ◽  
The Impact

Grain boundary triple junctions are the structural elements of a polycrystal. Recently it was recognized that they can strongly impact the microstructural evolution, and therefore there engender new opportunities to control and to design the grain microstructure of fine-grained and nanocrystalline materials due to their effect on recovery, recrystallization and grain growth. The measurement of triple junction energy and mobility is thus of great importance. The line energy of a triple junction constructs an additional driving force of grain growth. Taking the triple line energy into account, a modified form of the Zener force and the Gibbs-Thomson relation can be derived to reveal the influence of the triple line energy on second phase particles and the change of the equilibrium concentration of vacancies in the vicinity of voids at a grain boundary. The impact of triple junctions on the sintering of nanopowders is discussed. The role of “grain boundary - free surface” triple lines in the adhesive contact formation between spherical nanoparticles is considered. It is shown that there is a critical value of the triple line energy above which the nanoparticles do not stick together. Based on this result, a new nanoparticle agglomeration mechanism is proposed, which accounts for the formation of large agglomerates of crystallographically aligned nanoparticles during the nanopowder processing.

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.

Athermal Motion of Grain Boundaries, Twins and Triple Junctions in Zn

2004 ◽  
Vol 467-470 ◽  
pp. 801-806 ◽  
Author(s):  
Vera G. Sursaeva
Keyword(s):  
Thermal Expansion ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Triple Junction ◽  
Triple Junctions ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
The Difference ◽  
The Individual ◽  
Individual Grains

When a bicrystal or polycrystal are subjected to a change in temperature, the individual responses of the two adjoining crystals may differ in a manner, which tends to produce a dilatational mismatch along grain boundaries. If compatibility is to be retained along the interface, an additional set of stresses must then be generated in order to conserve this compatibility. ‘Compatibility stresses’ will also be generated whenever a polycrystal is heated or cooled and the thermal expansion coefficients of the individual grains are different due to thermal expansion anisotropy. In such cases adjacent grains will attempt to change dimensions and develop mismatches by amounts controlled by the parameter Δa*ΔΤ, where Δa is the difference between the thermal expansion coefficients in the appropriate directions, and ΔΤ is the temperature change. These ‘compatibility stresses’ may be relieves if grain boundary motion, triple junction migration and grain growth are possible. These ‘compatibility stresses’ may play important role in the kinetic behavior of the microstructure ranging from influencing the behavior of lattice dislocations near the grain boundaries to promoting grain boundary and triple junction dragging or moving. The motion of the ‘special’ grain boundaries, triple junctions with ‘special’ grain boundaries and twins under the influence of internal mechanical stresses is the main subject of this paper.

scholarly journals Influence of Finite Mobilities of Triple Junctions on the Grain Morphology and Kinetics of Grain Growth

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 185
Author(s):  
Ernst Gamsjäger ◽  
Boris Gschöpf ◽  
Jiří Svoboda
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Triple Junction ◽  
Cell Model ◽  
Grain Morphology ◽  
Triple Junctions ◽  
Grain Sizes ◽  
Heat Treated ◽  
Niobium Microalloyed Steel ◽  
Kinetics Of

Grain boundary networks composed of equal microstructural elements were investigated in a recent paper. In this work a more complicated artificial grain topology consisting of one four-sided, two six-sided and one eight-sided grain is designed to further investigate the influence of grain boundary and triple junction mobilities on the kinetics of the system in more detail. Depending on the value of the equal mobility of all triple junctions, the initially square-shaped four-sided grain changes its shape to become more or less rectangular. This indicates that the grain morphology is influenced by the value of the mobility of the triple junctions. It is also demonstrated that a grain arrangement with low mobility triple junctions controlling the kinetics of grain growth enhances growth of the large eight-sided grains. In addition, grain growth is investigated for different values of mobilities of triple junctions and grain boundaries. A strong elongation of several grains is predicted by the modeling results for reduced mobilities of the microstructural grain boundary elements. The two-dimensional modeling results are compared to micrographs of a heat-treated titanium niobium microalloyed steel. This feature, namely the evolution of elongated grains, is observed in the micrograph due to the pinning effect of (Ti, Nb)C precipitates at elevated soaking temperatures of around 1100 °C. Furthermore, the experiments show that a broader distribution of the grain sizes occur at 1100 °C compared to soaking temperatures, where pinning due to precipitates plays a less prominent role. A widening of the distribution of the grain sizes for small triple junction mobilities is also predicted by the unit cell model.

scholarly journals Effects of Boron Doping on the Grain Growth Behaviour of γ/γ Nickel-Aluminium Alloy

1999 ◽  
Vol 580 ◽  
Author(s):  
Y.L. Chiu ◽  
A.H.W. Ngan
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Boron Doping ◽  
Growth Behaviour ◽  
Boron Doped ◽  
Retarding Effect ◽  
Disordered Layer ◽  
Grain Growth Kinetics ◽  
First Time ◽  
Kinetics Of

AbstractEffects of 0.5 at. % boron doping on Ni85Al γ/γ superalloys were investigated for the first time, yielding a number of observations not previously observed in the literature. First, the grain growth kinetics of both the doped and undoped alloys were found to disobey the simple Nielsen law d = Ctn but instead follow an equation of the type d = C ln(t) + C0. The constants C and C0 were found to be respectively 10.2 and 23.2 for the boron-free alloy, and 6.2 and 14.2 for the boron-doped alloy, i.e., the grain growth rate was retarded significantly upon boron doping. Such a retarding effect is thought to be due to the formation of a boron-nickel cosegregated zone observed at the grain boundaries of the doped alloy; the width of the zone, in μm's, is two to three orders of magnitude larger than the boron induced disordered layer found in nickel rich Ni3Al compounds doped with boron. Other associated effects of the cosegregated zone include a sharp increase in toughness, much better slip transmission across grains and reduced workhardening rates. Another intriguing point is that the γ precipitates were found to segregate to the grain boundaries in the boron-free alloy after cold rolling, but no such segregation of γ precipitates has been observed in the boron-doped alloy. The different deformation microstructures and the retarded grain growth rates upon boron doping will be discussed.

A microstructure evolution model including dislocation plasticity

2000 ◽  
Vol 652 ◽  
Author(s):  
Fabrizio Cleri ◽  
Gregorio D'Agostino
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Microstructure Evolution ◽  
Evolution Model ◽  
Monte Carlo Algorithm ◽  
Triple Junctions ◽  
Two Phase ◽  
Grain Rotation ◽  
Dislocation Plasticity ◽  
Phase Liquid

ABSTRACTWe present a stochastic microstructure evolution model applicable to grain growth and its recent extensions, in particular relative to dislocation plasticity. The model is implemented by means of numerical simulations based on the velocity Monte Carlo algorithm. It describes the evolution of a two-dimensional microstructure by tracking the motion of triple junctions, i.e. the vertices where three grain boundaries meet. Grain boundaries can be modeled as straight or curved segments; the misorientation dependence of both grain-boundary energies and mobilities can be included, as well as grain rotation. We show simple examples of normal, abnormal and oriented grain growth. The model is already capable of dealing with a two-phase (liquid-solid) system, to simulate both grain growth and grain dissolution in the liquid. Finally, we report preliminary results of a recent extension of the model to include mechanical deformation from dislocation plasticity.

Microstructure and Magnetic Properties of NdFeB Magnets Using Fluorides Nano-Coated Process

2010 ◽  
Vol 638-642 ◽  
pp. 1357-1361 ◽  
Author(s):  
Matahiro Komuro ◽  
Yuichi Satsu ◽  
Hiroyuki Suzuki
Keyword(s):  
Magnetic Properties ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Triple Junction ◽  
Aging Process ◽  
Triple Junctions ◽  
Ndfeb Magnets ◽  
Fcc Structure ◽  
Microstructure And Magnetic Properties

Nd2Fe14B magnets could be sintered using terbium fluoride coated Nd2Fe14B powders. Fluorine atoms were segregated at the triple junctions and grain boundary after sintering and aging process. NdOF with fcc structure was grown at the triple junction. Terbium atoms were also distributed near grain boundaries by interdiffusion between the fluoride and Nd2Fe14B. No fluorine atoms were detected in Nd2Fe14B phase. The coercivity for 0.5wt% terbium fluoride coated magnet showed 1.23 MA/m which was 1.2 times higher than that for non-coated magnet with 1.04MA/m. The distribution of terbium and fluorine atoms increases the coercivity without reduction of remanence.

scholarly journals Kinetics of Grain Boundary Networks Controlled by Triple Junction and Grain Boundary Mobility

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 977 ◽  
Author(s):  
Ernst Gamsjäger ◽  
Daniel Ogris ◽  
Jiří Svoboda
Keyword(s):  
Analytical Solution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Triple Junction ◽  
Irreversible Thermodynamics ◽  
Force Balance ◽  
Structural Elements ◽  
Grain Boundary Mobility ◽  
Kinetics Of

The kinetics of a triple junction of grain boundaries with distinct specific energies and mobilities and a finite mobility of the triple junction is investigated. The microstructure is approximated by different 2D settings consisting of typical structural elements. First, the migration of the triple point together with the adjacent grain boundaries, is simulated, assuming that the grains are infinitely large. Secondly, growth or shrinkage of finite n-sided grains is simulated by altering the boundary conditions and the results are compared to the already published analytical solution. The numerical results coincide with the corrected analytical solution. This solution can be derived either by applying the principle of maximum dissipation, or by applying the force balance at the triple junction within the framework of linear irreversible thermodynamics. The change of the area of infinite and finite grains is investigated analytically and numerically. By comparing the results of both approaches, the influence of the initial topology of the structural elements on the kinetics of grain growth can be estimated. Furthermore, the kinetics of grain growth of different idealized grain boundary networks is investigated. It is shown that square shaped grains surrounded by hexagons and dodecagons result in a more realistic grain growth scenarios than squares surrounded by octagons. A deviation from idealized grain boundary arrangements is e.g., observed, due to different triple junction mobilities, and the initially n-sided regular grain deforms in a complex manner.

Diffusion Controlled Grain Triple Junctions Wetting in Metals

2011 ◽  
Vol 309-310 ◽  
pp. 231-238 ◽  
Author(s):  
Boris S. Bokstein ◽  
S.A. Gulevsky ◽  
A.L. Petelin ◽  
A.O. Rodin
Keyword(s):  
Gibbs Energy ◽  
Grain Boundaries ◽  
Triple Junction ◽  
Polycrystalline Sample ◽  
Triple Junctions ◽  
Polycrystalline Metal ◽  
Diffusion Controlled ◽  
Melt Penetration ◽  
Two Stages ◽  
Boundary Lines

The interaction between liquid and solid metals where the liquid-solid interface contains three grain boundary lines which meet in triple junction point is considered. The assumption that the liquid grooves may be formed not only along grain boundaries but along triple junctions is presented. The variation of Gibbs energy during the formation of triangle pyramidal groove along triple junction is determined. The dependence of Gibbs energy variation from groove dimensions shows that the wetting of triple junctions occurs by lower temperatures than the wetting of grain boundaries. This result allows to take into account the existence of grain size effect on the liquid phase penetration depth into the polycrystalline sample. The proposed mechanism of wetting in polycrystalline metal contains two stages: the outstrip melt penetration along triple junctions and the liquid grooving on grain boundaries forming the triple junctions. One of the processes – triple junction diffusion or liquid diffusion – may control the wetting in the polycrystalline sample.

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