The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Gregory S. Rohrer - One of the best experts on this subject based on the ideXlab platform.
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The role of Grain Boundary energy in Grain Boundary complexion transitions
Current Opinion in Solid State and Materials Science, 2016Co-Authors: Gregory S. RohrerAbstract:Abstract Recent findings about the role of the Grain Boundary energy in complexion transitions are reviewed. Grain Boundary energy distributions are most commonly evaluated using measurements of Grain Boundary thermal grooves. The measurements demonstrate that when a stable high temperature complexion co-exists with a metastable low temperature complexion, the stable complexion has a lower energy. It has also been found that the changes in the Grain Boundary energy lead to changes in the Grain Boundary character distribution. Finally, recent experimental observations are consistent with the theoretical prediction that higher energy Grain boundaries transform at lower temperatures than relatively lower energy Grain boundaries. To better control microstructures developed through Grain growth, it is necessary to learn more about the mechanism and kinetics of complexion transitions.
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Grain Boundary Complexions
Acta Materialia, 2014Co-Authors: Patrick R. Cantwell, Gregory S. Rohrer, Ming Tang, Shen J. Dillon, Jian Luo, Martin P. HarmerAbstract:Abstract Grain boundaries exhibit phase-like behavior in which their structure, chemistry and properties may change discontinuously at critical values of thermodynamic parameters such as temperature, pressure and chemical potential. Therefore, Grain boundaries (and other interfaces such as surfaces and heterophase boundaries) can be treated as thermodynamically stable interfacial states. To differentiate these interfacial states from bulk phases, the term “complexion” has been introduced. A variety of terminology has been used to describe complexions and complexion transitions. In many cases, several terms exist that describe essentially the same phenomenon. We give an overview of complexion-related terminology, suggest a preferred nomenclature and discuss a classification framework that can be used to categorize complexions and complexion transitions. The field of Grain Boundary complexions has evolved rapidly in the past decade due to advances in experimental equipment – in particular, aberration-corrected transmission electron microscopy – and progress in computational simulation methods. Grain Boundary complexion transitions are the root cause of a wide variety of materials phenomena – such as abnormal Grain growth, Grain Boundary embrittlement and activated sintering – that have defied mechanistic explanation for years. In this overview, we review the history and theory of Grain Boundary complexion transitions, their role in materials processing and their effect on materials properties.
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Grain Boundary energy anisotropy: a review
Journal of Materials Science, 2011Co-Authors: Gregory S. RohrerAbstract:This paper reviews findings on the anisotropy of the Grain Boundary energies. After introducing the basic concepts, there is a discussion of fundamental models used to understand and predict Grain Boundary energy anisotropy. Experimental methods for measuring the Grain Boundary energy anisotropy, all of which involve application of the Herring equation, are then briefly described. The next section reviews and compares the results of measurements and model calculations with the goal of identifying generally applicable characteristics. This is followed by a brief discussion of the role of Grain Boundary energies in nucleating discontinuous transitions in Grain Boundary structure and chemistry, known as complexion transitions. The review ends with some questions to be addressed by future research and a summary of what is known about Grain Boundary energy anisotropy.
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five parameter Grain Boundary distribution of commercially Grain Boundary engineered nickel and copper
Acta Materialia, 2008Co-Authors: Valerie Randle, Gregory S. Rohrer, Herbert M Miller, M Coleman, G T OwenAbstract:Abstract The five-parameter Grain Boundary distributions of Grain Boundary engineered nickel and copper specimens have been analyzed in detail. The relative areas of {1 1 1} planes in the entire population did not increase as a result of Grain Boundary engineering (GBE) and, in the Σ3-excluded population, decreased after GBE. This decrease occurred because the majority of the newly generated Σ3 Grain boundaries were not coherent twins with {1 1 1} Grain Boundary plane orientations. GBE increased the proportion of Σ3 Boundary length that was vicinal-to-{1 1 1} and the proportion of asymmetrical 〈1 1 0〉 tilt boundaries. There was a clear propensity for selection of particular planes or plane combinations which were associated with low energy. These plane types were analyzed in some detail, and it was shown that many of these boundaries were asymmetrical tilts comprising (or vicinal to) at least one low-index plane.
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The distribution of Grain Boundary planes in polycrystals
JOM, 2007Co-Authors: Gregory S. RohrerAbstract:During the last ten years, techniques have been developed to measure the distribution of Grain boundaries in polycrystals as a function of both lattice misorientation and Grain Boundary plane orientation. This paper presents a brief overview of the techniques used for these measurements and the principle findings of studies implementing these techniques. The most significant findings are that Grain Boundary plane distributions are anisotropic, that they are scale invariant during normal Grain growth, that the most common Grain Boundary planes are those with low surface energies, that the Grain Boundary populations are inversely correlated with the Grain Boundary energy, and that the coincident site lattice number is a poor predictor of the Grain Boundary energy and population.
Valerie Randle - One of the best experts on this subject based on the ideXlab platform.
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Grain Boundary texture
Materials Science Forum, 2010Co-Authors: Valerie Randle, Richard A. L. JonesAbstract:Recently the distribution of Grain Boundary planes in metals and other materials has begun to be studied in addition to the misorientation distribution. It has been found that a ‘Grain Boundary texture’, i.e. a non-random distribution of Grain Boundary planes, often exists. The present paper will show examples of Grain Boundary texture taken from austenitic stainless steel and rocksalt. The characteristics of the Grain Boundary texture will be described in terms of low-index Boundary planes and tilt/twist descriptors. Reasons for the formation of the particular Grain Boundary texture and possibilities for exploitation via Grain Boundary engineering will be discussed.
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Role of Grain Boundary plane in Grain Boundary engineering
Materials Science and Technology, 2010Co-Authors: Valerie RandleAbstract:AbstractThere is an increasing amount of interest in Grain Boundary engineering (GBE) to improve the properties of the Grain Boundary network. In general, research has concentrated on use of a Grain Boundary misorientation based approach, namely, the coincidence site lattice (CSL), to categorise 'special' boundaries. The present paper presents the case that the specialness of Grain boundaries is based on having at least one low index plane at the Boundary, rather than because the Boundary is a CSL type. It is shown that Grain Boundary planes play a pivotal role in GBE, and hence, an approach which focuses on the plane is advocated. Some potential routes for 'Grain Boundary plane engineering' are discussed.
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five parameter Grain Boundary distribution of commercially Grain Boundary engineered nickel and copper
Acta Materialia, 2008Co-Authors: Valerie Randle, Gregory S. Rohrer, Herbert M Miller, M Coleman, G T OwenAbstract:Abstract The five-parameter Grain Boundary distributions of Grain Boundary engineered nickel and copper specimens have been analyzed in detail. The relative areas of {1 1 1} planes in the entire population did not increase as a result of Grain Boundary engineering (GBE) and, in the Σ3-excluded population, decreased after GBE. This decrease occurred because the majority of the newly generated Σ3 Grain boundaries were not coherent twins with {1 1 1} Grain Boundary plane orientations. GBE increased the proportion of Σ3 Boundary length that was vicinal-to-{1 1 1} and the proportion of asymmetrical 〈1 1 0〉 tilt boundaries. There was a clear propensity for selection of particular planes or plane combinations which were associated with low energy. These plane types were analyzed in some detail, and it was shown that many of these boundaries were asymmetrical tilts comprising (or vicinal to) at least one low-index plane.
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Orientation distribution of Σ3 Grain Boundary planes in ni before and after Grain Boundary engineering
Materials Science Forum, 2007Co-Authors: Herbert M Miller, Valerie Randle, Chang-soo Kim, J. Gruber, Gregory S. RohrerAbstract:The distribution of Grain Boundary plane orientations in polycrystalline Ni has been measured before and after Grain Boundary engineering. The Grain Boundary engineered microstructure has a relatively higher concentration of Σ3 Grain boundaries and, when compared to the initial structure, more of these boundaries have orientations that are inclined by more than 10° from the (111) orientation of the ideal coherent twin. Although the conventionally measured Grain size is not affected by the Grain Boundary engineering process, the average size of the regions containing only Σ3n Grain boundaries increases by nearly a factor of two. The observations indicate that the increase in the relative population of Σ3 Grain boundaries results both from the preferential elimination of random Grain boundaries and the generation of new Σ3 Grain boundaries which do not have (111) Grain Boundary plane orientations.
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Distribution of misorientations and Grain Boundary planes in Grain Boundary engineered brass
Materials Science and Technology, 2005Co-Authors: Valerie Randle, Gregory S. Rohrer, C.-s. KimAbstract:Abstract The present paper reports the application of a five parameter determination of Grain Boundary types to Grain Boundary engineered α brass. Approximately 20 000 Grains constituted the total sample population, giving rise to more than 77 000 Grain Boundary line segments. This is the first time that the orientation of a large sample population of Grain Boundary planes has been measured in a Grain Boundary engineered material. The most important findings of the investigation were that the distribution of planes showed a prevalence of 〈 110 〉 tilt boundaries, especially asymmetric tilt types, and the presence of 〈 111 〉 twist boundaries. This distribution is a consequence of the low energy of these Boundary types. Furthermore, more than three-quarters of boundaries could be considered to be 'potentially special'. The presence of these boundaries greatly fragmented the Grain Boundary network. This fragmentation is probably a key factor in the development of superior properties in a Grain Boundary engine...
Allan F. Bower - One of the best experts on this subject based on the ideXlab platform.
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Aluminum Σ3 Grain Boundary sliding enhanced by vacancy diffusion
Acta Materialia, 2010Co-Authors: Paul E. Krajewski, Allan F. BowerAbstract:Abstract Grain Boundary sliding is an important deformation mechanism for elevated temperature forming processes. Molecular dynamics simulations are used to investigate the effect of vacancies in the Grain Boundary vicinity on the sliding of Al bi-crystals at 750 K. The threshold stress for Grain Boundary sliding was computed for a variety of Grain boundaries with different structures and energies. These structures included one symmetrical tilt Grain Boundary and five asymmetrical tilt Grain boundaries. Without vacancies, low energy Σ3 Grain boundaries exhibited significantly less sliding than other high energy Grain boundaries. The addition of vacancies to Σ3 Grain boundaries decreased the threshold stress for Grain Boundary sliding by increasing the Grain Boundary diffusivity. A higher concentration of vacancies enhanced this effect. The influence of vacancies on Grain Boundary diffusivity and Grain Boundary sliding was negligible for high energy Grain boundaries, due to the already high atom mobility in these boundaries.
Christian Brandl - One of the best experts on this subject based on the ideXlab platform.
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The influence of Grain Boundary structure upon damage evolution at Grain Boundary interfaces
2012Co-Authors: Alejandro G. Perez-bergquist, Christian Brandl, Juan P. Escobedo, Carl P. Trujillo, Ellen K. Cerreta, George T Gray Ill, Timothy C. GermannAbstract:In a prior work, it was found that Grain Boundary structure strongly influences damage evolution at Grain boundaries in copper samples subjected to either shock compression or incipient spall. Here, several Grain boundaries with different Grain Boundary structures, including a {Sigma}3 (10-1) Boundary, are interrogated via conventional transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) to investigate the effects of atomic-scale structural differences on Grain Boundary strength and mobility. Boundaries are studied both before and after shock compression at a peak shock stress of 10 GPa. Results of the TEM and HRTEM work are used in conjunction with MD modeling to propose a model for shock-induced damage evolution at Grain Boundary interfaces that is dependent upon coincidence.
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Coupled Grain Boundary motion in a nanocrystalline Grain Boundary network
Scripta Materialia, 2011Co-Authors: M. Velasco, H. Van Swygenhoven, Christian BrandlAbstract:Coupled Grain Boundary motion was simulated in a three-dimensional nanocrystalline Al Grain Boundary network using molecular dynamics. It is shown that, in spite of the triple junction constraints, a symmetrical Sigma 75 tilt Boundary can migrate during the microplastic regime with the same coupling factor as when simulated in a bicrystal configuration. After reaching the full plastic regime, dislocations start coming into play, changing the Grain Boundary structure and hindering further coupled motion. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Pavel Lejček - One of the best experts on this subject based on the ideXlab platform.
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Entropy-dominated Grain Boundary segregation
Journal of Materials Science, 2021Co-Authors: Pavel Lejček, S. HofmannAbstract:The phenomenon of entropy-dominated Grain Boundary segregation is introduced and discussed. Numerous examples of the Grain boundaries and solutes exhibiting this phenomenon are compiled and predicted for example of α-iron-based alloys and other host materials. Consequences of entropy-dominated Grain Boundary segregation for Grain size stabilization and intergranular embrittlement are shown. Graphical abstract
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Grain Boundary Segregation in Metals - Grain Boundary segregation in metals
Springer Series in Materials Science, 2010Co-Authors: Pavel LejčekAbstract:I. Introduction II. Grain boundaries: structure, description and thermodynamics III. Approaches to Study Grain Boundary Segregation IV. Models of Equilibrium Grain Boundary Segregation V. Effect of Variables on Equilibrium Grain Boundary Segregation VI. Principles of Non-Equilibrium Segregation VII. Grain Boundary Segregation and Related Phenomena and metallurgical phenomena VIII. Concluding remarks
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Grain Boundary segregation in metals
gbsm, 2010Co-Authors: Pavel LejčekAbstract:I. Introduction II. Grain boundaries: structure, description and thermodynamics III. Approaches to Study Grain Boundary Segregation IV. Models of Equilibrium Grain Boundary Segregation V. Effect of Variables on Equilibrium Grain Boundary Segregation VI. Principles of Non-Equilibrium Segregation VII. Grain Boundary Segregation and Related Phenomena and metallurgical phenomena VIII. Concluding remarks
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Reversed anisotropy of Grain Boundary properties and its effect on Grain Boundary engineering
Acta Materialia, 2010Co-Authors: Pavel Lejček, Aleš Jäger, Viera GärtnerováAbstract:Abstract Data on anisotropy of Grain Boundary properties are frequently published. In some cases, when they show the reverse course of structural dependence than is expected, they can seem confusing. Examples of this “reversed anisotropy” found for Grain Boundary segregation, diffusion and migration are presented. We demonstrate that the reversed anisotropy of Grain Boundary properties is caused by the compensation effect. This can have serious consequences for Grain Boundary engineering. It is also suggested that Grain boundaries can be classified specifically and generally solely on the basis of well-defined thermodynamic parameters.
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Grain Boundary Segregation in Metals
Springer Series in Materials Science, 2010Co-Authors: Pavel LejčekAbstract:Grain boundaries are important structural components of polycrystalline materials used in the vast majority of technical applications. Because Grain boundaries form a continuous network throughout such materials, their properties may limit their practical use. One of the serious phenomena which evoke these limitations is the Grain Boundary segregation of impurities. It results in the loss of Grain Boundary cohesion and consequently, in brittle fracture of the materials. The current book deals with fundamentals of Grain Boundary segregation in metallic materials and its relationship to the Grain Boundary structure, classification and other materials properties
