The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Nong-moon Hwang - One of the best experts on this subject based on the ideXlab platform.
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three dimensional monte carlo simulation for the effect of precipitates and sub boundaries on Abnormal Grain Growth
Scripta Materialia, 2012Co-Authors: Changsoo Park, Hyungki Park, Byeongjoo Lee, Chanhee Han, Nong-moon HwangAbstract:We performed three-dimensional Monte Carlo simulations to investigate the effects of precipitates and sub-boundaries on the Abnormal Grain Growth. The simulation showed that both precipitates and sub-boundaries play an important role in inducing Abnormal Grain Growth by solid-state wetting along triple junctions. The morphology evolved by the simulation is very similar to that observed during Abnormal Grain Growth of a polycrystalline aluminum alloy.
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Abnormal Grain Growth induced by sub boundary enhanced solid state wetting analysis by phase field model simulations
Acta Materialia, 2009Co-Authors: Pilryung Cha, David J Srolovitz, Nong-moon HwangAbstract:Abstract Abnormal Grain Growth (AGG) was approached by a new concept of sub-boundary-enhanced solid-state wetting using a phase-field model (PFM) simulation. If Grains have sub-boundaries of very low-energy, they increase the probability of growing by solid-state wetting, compared with other Grains of moderate anisotropy in Grain boundary energy. As a result, the Grains with sub-boundaries have an exclusive Growth advantage and can grow Abnormally. These aspects are shown in two- and three-dimensional PFM simulations.
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new understanding of Abnormal Grain Growth approached by solid state wetting along Grain boundary or triple junction
Materials Science Forum, 2004Co-Authors: Nong-moon HwangAbstract:Although it has been generally believed that the advantage of the Grain boundary mobility induces Abnormal Grain Growth (AGG), it is suggested that the advantage of the low Grain boundary energy, which favors the Growth by solid-state wetting, induces AGG. Analyses based on Monte Carlo (MC) simulation show that the approach by solid-state wetting could explain AGG much better than that by Grain boundary mobility. AGG by solid-state wetting is supported not only by MC simulations but also by the experimental observation of microstructure evolution near or at the Growth front of Abnormally growing Grain. The microstructure shows island Grains and solid-state wetting along Grain boundary and triple junction.
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microstructural evidence of Abnormal Grain Growth by solid state wetting in fe 3 si steel
Journal of Applied Physics, 2004Co-Authors: Hyun Soo Park, Dohyeon Kim, Nong-moon Hwang, Young-chang Joo, Chanhee Han, Jaekwan KimAbstract:In this investigation, the mechanism of Abnormal Grain Growth in Fe-3%Si steel was based on the microstructure evolution at the Growth front of Grains undergoing the Abnormal Growth. The most striking feature in the Growth of Abnormal Grains was the penetration along the Grain boundary of neighboring Grains. This is energetically possible if the energy of the penetrated Grain boundary is higher than the sum of the energy of two other Grain boundaries shared by the penetrating Abnormal Grain. Along the Growth front of an investigated Abnormally growing Grain, 15 out of 1381 triple junctions showed the clear microstructural evidence of the Grain boundary penetration by the Abnormal Grain. Misorientation measurements of 34 penetrated Grain boundaries using electron backscattered diffraction showed that not a single boundary has a low angle, implying that the penetrated Grain boundaries have the high energy. These results are best explained by the Abnormal Grain Growth with solid-state wetting.
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effect of the liquid forming additive content on the kinetics of Abnormal Grain Growth in alumina
Journal of the American Ceramic Society, 2003Co-Authors: Jung Hyuck Ahn, Seonghyeon Hong, Nong-moon Hwang, Jehun Lee, Dohyeon KimAbstract:Alumina specimens with various amounts of CaO and SiO2 (1:2 ratio) were prepared, and their Abnormal Grain Growth (AGG) kinetics were investigated. A plot of the area fraction covered by Abnormal Grains versus log (sintering time) had a sigmoidal shape with an apparent incubation period before the onset of AGG. The overall kinetics of AGG was similar to that of a phase transformation controlled by nucleation and Growth. The incubation time and the end point of AGG were strongly dependent on the amount of liquid-forming additives. Correspondingly, the final microstructure was affected by the liquid content: a large Grain size and a high aspect ratio at low liquid content and a small Grain size and a low aspect ratio at high liquid content.
Nong M Hwang - One of the best experts on this subject based on the ideXlab platform.
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monte carlo simulations of Abnormal Grain Growth by sub boundary enhanced solid state wetting
Scripta Materialia, 2008Co-Authors: Dabin Lee, Byeongjoo Lee, Nong M HwangAbstract:The role of sub-boundaries in inducing Abnormal Grain Growth (AGG) by solid-state wetting was studied using a Monte Carlo simulation. Sub-boundaries of very low energy in a Grain markedly increase the probability of solid-state wetting and thereby cause the Grain to grow Abnormally. The sub-boundary-enhanced solid-state wetting has the unique feature of inducing AGG without advantages such as high-mobility or low-energy boundaries between an Abnormally growing Grain and matrix Grains.
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microstructural evolution during sintering of tio2 sio2 doped alumina mechanism of anisotropic Abnormal Grain Growth
Acta Materialia, 2002Co-Authors: Okseon Kwon, Dohyeon Kim, Seonghyeon Hong, Jungsuk Lee, Uijin Chung, Nong M HwangAbstract:Abstract Microstructural changes that occurred during the sintering of alumina doped with TiO 2 and SiO 2 have been investigated. The kinetics of normal Grain Growth at the initial stage is retarded by the dopant segregation at the Grain boundaries. However, due to the accumulation of dopants at the Grain boundaries during Grain Growth, its concentration at the boundaries ultimately exceeds the solubility limit and an intergranular liquid film emerges. The appearance of the liquid and the resulting increase in boundary mobility are confirmed to be the main cause of Abnormal Grain Growth. For the Abnormal Grains, a liquid phase is observed at the basal surface in most cases, while the edges of these Grains were partially wetted. Anisotropic or directional Growth of the Abnormal Grains is explained in terms of the enhanced Growth kinetics due to the re-entrant edges formed by Grain boundaries at the non-basal planes.
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ostwald ripening kinetics of angular Grains dispersed in a liquid phase by two dimensional nucleation and Abnormal Grain Growth
Journal of The European Ceramic Society, 2002Co-Authors: Muyungkoo Kang, Dohyeon Kim, Nong M HwangAbstract:Abstract Based on the fact that the angular shape of solid Grains dispersed in the liquid matrix indicates a singular interface, the coarsening kinetics of angular Grains was formulated based on 2-dimensional (2-D) nucleation and solved numerically. For comparison, diffusion-controlled coarsening of Grains with a spherical shape was also solved numerically. The solutions showed that coarsening by 2-D nucleation induced Abnormal Grain Growth whilst diffusion-controlled coarsening did not. This result agrees with the general experimental observation that the Abnormal Grain Growth in liquid phase sintering takes place exclusively in the system with angular Grains. The ratio of the largest Grain size to the average increased monotonously with time in coarsening by 2-D nucleation whilst it decreased in diffusion-controlled coarsening. The artificially-added large Grain (10 times larger than the average) became the Abnormal Grain in 2-D nucleation controlled coarsening but did not in diffusion-controlled coarsening.
Dohyeon Kim - One of the best experts on this subject based on the ideXlab platform.
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anisotropic Abnormal Grain Growth in tio2 sio2 doped alumina
Journal of the American Ceramic Society, 2004Co-Authors: Youngmin Kim, Seonghyeon Hong, Dohyeon KimAbstract:The effect of TiO 2 /SiO 2 addition on the Grain Growth of alumina was reinvestigated. TiO 2 promoted the Grain Growth, but there was no Abnormal Grain Growth. However, codoping of TiO 2 and SiO 2 resulted in a duplex microstructure consisting of large platelike Grains, ∼800 μm long and ∼100 μm thick, and fine matrix Grains. The observed anisotropic Abnormal Grain Growth was explained in terms of liquid formation during heat treatment.
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microstructural evidence of Abnormal Grain Growth by solid state wetting in fe 3 si steel
Journal of Applied Physics, 2004Co-Authors: Hyun Soo Park, Dohyeon Kim, Nong-moon Hwang, Young-chang Joo, Chanhee Han, Jaekwan KimAbstract:In this investigation, the mechanism of Abnormal Grain Growth in Fe-3%Si steel was based on the microstructure evolution at the Growth front of Grains undergoing the Abnormal Growth. The most striking feature in the Growth of Abnormal Grains was the penetration along the Grain boundary of neighboring Grains. This is energetically possible if the energy of the penetrated Grain boundary is higher than the sum of the energy of two other Grain boundaries shared by the penetrating Abnormal Grain. Along the Growth front of an investigated Abnormally growing Grain, 15 out of 1381 triple junctions showed the clear microstructural evidence of the Grain boundary penetration by the Abnormal Grain. Misorientation measurements of 34 penetrated Grain boundaries using electron backscattered diffraction showed that not a single boundary has a low angle, implying that the penetrated Grain boundaries have the high energy. These results are best explained by the Abnormal Grain Growth with solid-state wetting.
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effect of the liquid forming additive content on the kinetics of Abnormal Grain Growth in alumina
Journal of the American Ceramic Society, 2003Co-Authors: Jung Hyuck Ahn, Seonghyeon Hong, Nong-moon Hwang, Jehun Lee, Dohyeon KimAbstract:Alumina specimens with various amounts of CaO and SiO2 (1:2 ratio) were prepared, and their Abnormal Grain Growth (AGG) kinetics were investigated. A plot of the area fraction covered by Abnormal Grains versus log (sintering time) had a sigmoidal shape with an apparent incubation period before the onset of AGG. The overall kinetics of AGG was similar to that of a phase transformation controlled by nucleation and Growth. The incubation time and the end point of AGG were strongly dependent on the amount of liquid-forming additives. Correspondingly, the final microstructure was affected by the liquid content: a large Grain size and a high aspect ratio at low liquid content and a small Grain size and a low aspect ratio at high liquid content.
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microstructural evolution during sintering of tio2 sio2 doped alumina mechanism of anisotropic Abnormal Grain Growth
Acta Materialia, 2002Co-Authors: Okseon Kwon, Dohyeon Kim, Seonghyeon Hong, Jungsuk Lee, Uijin Chung, Nong M HwangAbstract:Abstract Microstructural changes that occurred during the sintering of alumina doped with TiO 2 and SiO 2 have been investigated. The kinetics of normal Grain Growth at the initial stage is retarded by the dopant segregation at the Grain boundaries. However, due to the accumulation of dopants at the Grain boundaries during Grain Growth, its concentration at the boundaries ultimately exceeds the solubility limit and an intergranular liquid film emerges. The appearance of the liquid and the resulting increase in boundary mobility are confirmed to be the main cause of Abnormal Grain Growth. For the Abnormal Grains, a liquid phase is observed at the basal surface in most cases, while the edges of these Grains were partially wetted. Anisotropic or directional Growth of the Abnormal Grains is explained in terms of the enhanced Growth kinetics due to the re-entrant edges formed by Grain boundaries at the non-basal planes.
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ostwald ripening kinetics of angular Grains dispersed in a liquid phase by two dimensional nucleation and Abnormal Grain Growth
Journal of The European Ceramic Society, 2002Co-Authors: Muyungkoo Kang, Dohyeon Kim, Nong M HwangAbstract:Abstract Based on the fact that the angular shape of solid Grains dispersed in the liquid matrix indicates a singular interface, the coarsening kinetics of angular Grains was formulated based on 2-dimensional (2-D) nucleation and solved numerically. For comparison, diffusion-controlled coarsening of Grains with a spherical shape was also solved numerically. The solutions showed that coarsening by 2-D nucleation induced Abnormal Grain Growth whilst diffusion-controlled coarsening did not. This result agrees with the general experimental observation that the Abnormal Grain Growth in liquid phase sintering takes place exclusively in the system with angular Grains. The ratio of the largest Grain size to the average increased monotonously with time in coarsening by 2-D nucleation whilst it decreased in diffusion-controlled coarsening. The artificially-added large Grain (10 times larger than the average) became the Abnormal Grain in 2-D nucleation controlled coarsening but did not in diffusion-controlled coarsening.
P R Rios - One of the best experts on this subject based on the ideXlab platform.
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topological theory of Abnormal Grain Growth
Acta Materialia, 2006Co-Authors: P R Rios, M E GlicksmanAbstract:Abstract Theories of Abnormal Grain Growth (AGG) treat this interesting phenomenon in terms of the relative Grain size, or Grain radius, of the Abnormal Grains. This study, by contrast, treats AGG in terms of concepts that include both the boundary curvature and the number of faces of the Abnormal Grain. First, we formulate a topological AGG criterion: if a “candidate” Grain is undergoing Abnormal Growth, then its number of faces is increasing with time. AGG initiation in a pinned matrix is analyzed. An “AGG map” summarizes the results of this analysis. Finally, we derive analytical expressions for the number of faces as a function of time for AGG in a pinned matrix, and for AGG in a matrix that is free to undergo normal Grain Growth. Consideration of the topological features of polyhedral Grains introduces new aspects important to our understanding of the kinetics of AGG.
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texture evolution during normal and Abnormal Grain Growth in an al 1 wt mn alloy
Acta Materialia, 2001Co-Authors: P R Rios, G GottsteinAbstract:Abstract The texture evolution during normal and Abnormal Grain Growth in an Al–1 wt% Mn alloy was studied. Prior to deformation the amount of precipitates was enhanced by annealing at 500°C for 4 days (3.5×10 5 s). After 80% cold rolling and recrystallization the alloy had a weak cube ({001}〈100〉) texture and a minority texture component, the A component, related to the cube texture by a Σ 5 (36.9°〈100〉) orientation relationship. After limited normal Grain Growth both the cube and the A component were strengthened. However, both after Abnormal Grain Growth and after extensive normal Grain Growth, the A component became the dominant texture component. The result is interpreted based on the assumption that Σ 5 boundaries can migrate faster than other boundaries in this alloy. Possible reasons to support this hypothesis are discussed. The situation bears resemblance to Abnormal Grain Growth in Fe–3 wt% Si alloys, where special properties are attributed to Σ 9 boundaries.
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Abnormal Grain Growth kinetics of batio3 with an excess tio2
Acta Materialia, 1998Co-Authors: P R Rios, T Yamamoto, T Kondo, Taketo SakumaAbstract:Abstract The Abnormal Grain Growth of BaTiO3 containing an excess of 0.1, 0.2, and 0.4 mol% of TiO2 is studied. It is found that the matrix Grain size depends on TiO2 excess but does not change with annealing temperature or time characterizing that the matrix Grain Growth is strongly suppressed. The number of Abnormal Grains per unit of volume also behaves in a similar way indicating that the Abnormal Grains originated right in the beginning of the reaction in a situation analogous to a site-saturated transformation. The evolution of the volume fraction of the Abnormal Grains with time has an unusual feature: the maximum volume fraction, for a given TiO2 excess, is less than one for lower annealing temperatures but increases with annealing temperature. A model is proposed to describe the kinetics that agrees well with measured data. Abnormal Grain Growth has been confirmed to occur in the solid state below the eutectic temperature. Nonetheless both experimental and theoretical results suggest that Abnormal Grain Growth kinetics is significantly faster above the eutectic temperature. The nature of the pinning force in BaTiO3 containing an excess of TiO2 is also discussed in detail.
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Abnormal Grain Growth development from uniform Grain size distributions
Acta Materialia, 1997Co-Authors: P R RiosAbstract:The development of Abnormal Grain Growth from uniform Grain size distributions pinned by particles is examined. The main assumption is that a locally lower pinning force adjacent to a large Grain can cause this Grain to grow Abnormally. The case of a matrix pinned by unstable particles is considered in detail. A quantitative criterion is derived which shows the interplay among the variables involved. From this it is shown how both deterministic and probabilistic factors contribute to Abnormal Grain Growth. Practical implications are discussed with particular emphasis on why Abnormal Grain Growth can be so difficult to control. The present treatment offers a new and plausible rationale for the development of Abnormal Grain Growth from uniform Grain size distributions containing unstable particles.
Rajiv S Mishra - One of the best experts on this subject based on the ideXlab platform.
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inhibition of Abnormal Grain Growth during hot deformation behavior of friction stir processed 5083 al alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: M A Garciabernal, Rajiv S Mishra, Ravi Verma, D HernandezsilvaAbstract:Abstract Friction stir processing (FSP) has demonstrated to refine the microstructure of different alloys resulting in superior mechanical properties. Abnormal Grain Growth (AGG) has been recognized as a critical issue during hot deformation of FSPed Al alloys. 5083 Al alloys with different Mn content were subjected to heat treatments at 350 and 535 °C before FSP to avoid AGG during subsequent hot deformation. As a result, heat treatment of 350 °C was able to retard AGG significantly. Also, an improvement in the refinement of the microstructure was observed. Consequently, a better ductility of 861% at elevated temperature was reached in the alloy with lower Mn content comparing with the same alloy without heat treatment prior to FSP.
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effect of process parameters on Abnormal Grain Growth during friction stir processing of a cast al alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010Co-Authors: Rajiv S Mishra, Saumyadeep Jana, John A Baumann, Glenn J GrantAbstract:The effects of process parameters and friction stir processing (FSP) run configurations on the stability of nugget microstructure at elevated temperatures were evaluated. Cast plates of an Al–7Si–0.6Mg alloy were friction stir processed using a combination of tool rotation rates and tool traverse speeds. All single pass runs showed some extent of Abnormal Grain Growth (AGG), whereas multi-pass runs were more resistant to AGG. Additionally, higher tool rotation rate was found to be beneficial for controlling AGG. These effects were analyzed by comparing the result of this work with other published results and AGG models.
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Abnormal Grain Growth in friction stir processed alloys
Scripta Materialia, 2008Co-Authors: Indrajit Charit, Rajiv S MishraAbstract:Abnormal Grain Growth can be a critical issue during the post-processing heat treatment of friction stir welded or processed aluminum alloys. Various theories have been proposed to elucidate the origin of this behavior. This viewpoint paper addresses the issues with reference to the mechanisms involved and their implications for friction stirred microstructures.
