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Log–log plot of the average grain size with respect to time for the calculation of growth exponent in case of GBM-driven growth, GR-driven growth and simultaneous GBM- and GR-driven growth
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Study of microstructure evolution in the form of grain growth in polycrystalline materials has been an important goal for material scientists as it drastically affects physical and mechanical properties. Specifically, nanocrystalline materials, which are known for their superior mechanical properties, are highly susceptible to grain growth even at...
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Heterogeneous grain structures may develop due to abnormal grain growth during processing of polycrystalline materials ranging from metals and alloys to ceramics. The phenomenon must be controlled in practical applications where typically homogeneous grain structures are desired. Recent advances in experimental and computational techniques have, th...
Zener drag and pinning in composites reinforced with cylindrical particles is investigated using three-dimensional phase-field simulations. Detailed systematic studies clarify the effect of relative orientation of the particle and length/diameter ratio on the kinetics of drag. It is shown that a combination of local equilibrium at junctions in cont...
Citations
... (7) with an advection term [130,137]. In order to simulate the grain coalescence due to both the grain rotation and grain boundary migration, a phase-field model with multiple order parameters is proposed [139]. In this model, the constitutive equation for the grain rotation induced by viscous sliding and the classical phase-field model for curvature-driven grain boundary migration are coupled. ...
... (7) with an advection term [131,138]. In order to simulate the grain coalescence due to both the grain boundary migration and grain rotation, a multi-order parameter phase-field model is proposed [140]. In this model, the constitutive equation of viscous sliding induced grain rotation and the classical phase-field model for curvature-driven grain boundary migration are coupled. ...
Sintering, as a thermal process at elevated temperature below the melting point, is widely used to bond contacting particles into engineering products such as ceramics, metals, polymers, and cemented carbides. Modelling and simulation as important complement to experiments are essential for understanding the sintering mechanisms and for the optimization and design of sintering process. We share in this article a state-to-the-art review on the major methods and models for the simulation of sintering process at various length scales. It starts with molecular dynamics simulations deciphering atomistic diffusion process, and then moves to microstructure-level approaches such as discrete element method, Monte--Carlo method, and phase-field models, which can reveal subtle mechanisms like grain coalescence, grain rotation, densification, grain coarsening, etc. Phenomenological/empirical models on the macroscopic scales for estimating densification, porosity and average grain size are also summarized. The features, merits, drawbacks, and applicability of these models and simulation technologies are expounded. In particular, the latest progress on the modelling and simulation of selective and direct-metal laser sintering based additive manufacturing is also reviewed. Finally, a summary and concluding remarks on the challenges and opportunities are given for the modelling and simulations of sintering process.
... The PF model has been able to predict the microstructure evolution, qualitatively and quantitatively, under both elastic deformation [2,3,36,37] and plastic deformation [38][39][40][41]. The PF model can also apply for studying nucleation and growth in polycrystalline materials by using the active parameter tracking algorithm [42][43][44]. To understand the influence of an external magnetic field on the microstructure evolution, several theoretical studies also have been performed using the PF method by Toshioki Koyama [45], Yongmei M. Jin [46], and Backofen et al. [47,48]. ...
A constitutive model for diffuse interface description of magnetic field-induced grain boundary migration in polycrystalline metals is developed based on the laws of thermodynamics. Within this phase field modeling framework, simultaneous minimization of the total grain boundary energy and the stored magnetic energy within grains provides the driving force for grain growth in a polycrystal material exposure to a magnetic field. Using the available experimental data, phase field simulations of magnetic field induced grain growth in bicrystalline zinc and polycrystalline titanium with two-dimensional columnar microstructure are performed and the model is validated by demonstrating a qualitative and quantitative match with experimental data. Using the validated constitutive model, the effects of magnetic field intensity and direction on evolution of microstructure and polycrystalline texture in titanium are investigated. Quantitative simulation results show that under certain magnetic field directions and sufficient magnetic field intensity, the magnetic energy minimizing driving force can overcome the curvature driving force and cause texture evolution towards less magnetic energy grain orientations during annealing. However, magnetic fields with insufficient intensity or improper direction have negligible effect on grain coarsening by nearly normal grain growth. The desired magnetic field direction and intensity are quantitatively presented for cold-rolled and annealed sheet titanium samples.
... According to Figure 7(a)-(e), the original grain boundary completely disappeared, CaO grain continued to fuse and grow up, and a new grain boundary with lower energy is formed finally. The CaO grain boundary migra-tion rate in the lime samples is controlled mainly by grain boundary migration driver during the heating process [17,18]. ...
The volume stability caused by the hydration of f-CaO is one of the main obstacles to the comprehensive utilization of steel-making slag. In view of the f-CaO produced by incomplete dissolution of lime, it is necessary to strengthen the dissolution behavior of lime in the converter process. The reactivity of lime determines the dissolution efficiency and is closely related to its microstructure. The experimental results show that the reactivity and porosity of quick lime decrease and the average diameter of pore increases with an increase in temperature. The CaO crystals gradually grow up under the action of grain boundary migration. When the temperature increased from 1,350 to 1,600°C, the lime reactivity decreased from 237.60 to 40.60 mL, the porosity decreased from 30.55 to 15.91%, the average pore diameter increased from 159.10 to 1471.80 nm, and the average CaO particle size increased from 0.33 to 9.61 µm. The results indicate that reactivity is decreased because of the deformation and growth of CaO crystals and the decrease in porosity in reactive lime. This will cause an obstacle to the dissolution of lime and is not conducive to the control of f-CaO in slag.
... They [31] also obtained statistically and numerically reliable results during anisotropic evolution in a two-dimensional (2D) large grain system. Vuppuluri and Vedantam [32] studied the microstructure controlled by the GB migration and grain rotation through using a model considering the anisotropic GB energy. Recently, Shahnooshi et al. [23] investigated the effect of anisotropic grain boundary energy on the kinetics of stressed grain growth by a 2D phase field model. ...
A three-dimensional (3D) multiple phase field model, which takes into account the grain boundary (GB) energy anisotropy caused by texture, is established based on real grain orientations and Read–Shockley model. The model is applied to the grain growth process of polycrystalline Mg (ZK60) alloy to investigate the evolution characteristics in different systems with varying proportions of low-angle grain boundary (LAGB) caused by different texture levels. It is found that the GB energy anisotropy can cause the grain growth kinetics to change, namely, higher texture levels (also means higher LAGB proportion) result in lower kinetics, and vice versa . The simulation results also show that the topological characteristics, such as LAGB proportion and distribution of grain size, undergo different evolution characteristics in different systems, and a more serious grain size fluctuation can be caused by a higher texture level. The mechanism is mainly the slower evolution of textured grains in their accumulation area and the faster coarsening rate of non-textured grains. Therefore, weakening the texture level is an effective way for implementing a desired homogenized microstructure in ZK60 Mg alloy. The rules revealed by the simulation results should be of great significance for revealing how the GB anisotropy affects the evolution of polycrystalline during the grain growth after recrystallization and offer the ideas for processing the alloy and optimizing the microstructure.
The effects of the addition of AcOH and ethanol on phase composition and crystal growth behavior of La0.8Sr0.2MnO3 nanopowders prepared via sol-gel process were investigated. As a result, the phase composition of final products was not affected by the addition of ethanol or AcOH in the raw solution. The activation energy for crystal growth was firstly decreased and then increased with the continuous addition of ethanol or AcOH, while it was obviously influenced by the content of AcOH. After the addition of AcOH, the activation energy for crystal growth was reduced from 26.60 kJ/mol to 23.59 kJ/mol, and then was gradually augmented to 39.75 kJ/mol with the continuous increase. Correspondingly, the crystallite size of final products was controlled to be 48.5 nm, and the lowest activation energy for crystal growth of La0.8Sr0.2MnO3 nanopowders was obtained with water as the solvent and the AcOH/Mn molar ratio of 1:2, which was beneficial to the crystallization of La0.8Sr0.2MnO3 grains.
Grain growth and shrinkage are essential to the thermal and mechanical stability of nanocrystalline metals, which are assumed to be governed by the coordinated deformation between neighboring grain boundaries (GBs) in the nanosized grains. However, the dynamics of such coordination has rarely been reported, especially in experiments. In this work, we systematically investigate the atomistic mechanism of coordinated GB deformation during grain shrinkage in an Au nanocrystal film through combined state-of-the-art in situ shear testing and atomistic simulations. We demonstrate that an embedded nanograin experiences shrinkage and eventually annihilation during a typical shear loading cycle. The continuous grain shrinkage is accommodated by the coordinated evolution of the surrounding GB network via dislocation-mediated migration, while the final grain annihilation proceeds through the sequential dislocation-annihilation-induced grain rotation and merging of opposite GBs. Both experiments and simulations show that stress distribution and GB structure play important roles in the coordinated deformation of different GBs and control the grain shrinkage/annihilation under shear loading. Our findings establish a mechanistic relation between coordinated GB deformation and grain shrinkage, which reveals a general deformation phenomenon in nanocrystalline metals and enriches our understanding on the atomistic origin of structural stability in nanocrystalline metals under mechanical loading.
Monte Carlo (MC) simulation was used to predict the microstructural evolution and the kinetics of grain growth during heating of Zn–22Al dual phase alloy. As the prediction of MC simulation is based on virtual simulation time, time conversion plays a significant role in determining the recrystallization and growth kinetics of the alloy. The problem is more critical for the alloys in consideration that, they are composed of two phases with different grain boundary motilities. In this article, effort has been made to develop and modify the Monte Carlo algorithm of normal grain growth for simulating Ostwald ripening and grain growth in two-phase Zn–22Al alloy system. Grain-boundary migration (GBM) and the experimental data-based (EDB) models predict accurate relationship between simulation and real time among proposed relationship. It has been found that the grain growth of Zn–22Al is controlled by diffusion along grain boundaries (n = 4) and a reasonable agreement between the simulation and experimental results has been attained.
