Anisotropy of segregation at grain boundaries and surfaces

Wynblatt, P.; Chatain, Dominique

doi:10.1007/bf02586096

Cited by 159 publications

(95 citation statements)

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“…3;2018 Here is the grain boundary solute content (in mole), is the solute concentration within the grain and σ is the molar grain boundary area. Complete thermodynamic stabilization by grain boundary segregation as discussed in Darling et al (2013) is obtained when normalized grain boundary energy ( ⁄ ) equals with zero and the corresponding is minimum solute content for stabilization.The free surface segregation energyin terms of chemical and elastic effects is given by the classical Wynblatt and Ku bilayer grain boundary model (WK model) (Wynblatt & Ku, 1977;Wynblatt & Chatain, 2006)…”

Section: Phase and Microstructural Analysismentioning

confidence: 99%

Effect of Annealing on Microstructure, Grain Growth and Hardness of Nanocrystalline Cu-Zr Alloy Prepared by Cryogenic Ball Milling

Khobragade¹,

Sikdar²,

Kumar³

et al. 2018

JMSR

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Nanocrystalline Cu-0.75 at.%Zr alloy was synthesized by high energy ball milling under cryogenic temperature. To investigate the influence of 0.75 at.%Zr addition on thermal stabilization of nanocrystalline state of Copper, milled powder was annealed up to T/T m = 0.79 for 1h in an inert atmosphere. The microstructural changes of both milled and annealed powders were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Mechanical properties were determined in terms of hardness. It was found that addition of 0.75 at.%Zr can stabilize grain size at higher temperature, i.e., ~ 32 nm at 800 o C (T/Tm = 0.79). The hardness of Cu-0.75 at.%Zr at 800 o C was found to decrease by only ~ 13% as opposed to a 65% decrease in pure copper from cryomilled condition. The thermal stability of Cu-0.75 at.%Zr system at high temperatures was attributed to the kinetic stabilization, i.e., grain boundary pinning by intermetallic phases. Thermal stability contributions were assessed by thermodynamic models elicits added Zr is not sufficient for stabilization, rather kinetic stabilization (by intermetallic pinning of grain boundary) became active at higher annealing temperature.

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Section: Phase and Microstructural Analysismentioning

confidence: 99%

Effect of Annealing on Microstructure, Grain Growth and Hardness of Nanocrystalline Cu-Zr Alloy Prepared by Cryogenic Ball Milling

Khobragade¹,

Sikdar²,

Kumar³

et al. 2018

JMSR

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“…Here, we adopt a Wynblatt-Chatain multilayer adsorption model [33] to formulate an expression of γ GB using an Ising type lattice model (assuming that each lattice point is occupied by either Ni or Bi atoms). The following expression is derived for a "general" (100) twist GB (to represent the average general Σ ∞ GBs, for which the fraction of "broken bonds" is set to ensure that γ GB (0) /γ surface (0) = 1/3 to match the average value for "random" GBs in pure metals) to represent the average general GBs in Bi-doped Ni:…”

Section: Contents Lists Available At Sciencedirectmentioning

confidence: 99%

“…, where r Bi is the atomic radius of Bi and ΔE els 1 (=0.27 eV/atom for a Bi atom on the FCC Ni lattice) is obtained from the Friedel model [33]. The equilibrium compositional profiles are obtained by minimizing Eq.…”

Section: Contents Lists Available At Sciencedirectmentioning

confidence: 99%

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Calculation and validation of a grain boundary complexion diagram for Bi-doped Ni

Zhou

Zhang

et al. 2017

Scripta Materialia

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a b s t r a c t a r t i c l e i n f oA grain boundary (GB) "phase" (complexion) diagram is computed via a lattice type statistical thermodynamic model for the average general GBs in Bi-doped Ni. The predictions are calibrated with previously-reported density functional theory calculations and further validated by experiments, including both new and old aberrationcorrected scanning transmission electron microscopy characterization results as well as prior Auger electron spectroscopy measurements. This work supports a major scientific goal of developing GB complexion diagrams as an extension to bulk phase diagrams and a useful materials science tool.© 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Grain boundaries (GBs) can undergo phase-like transformations, for example, premelting [1] or adsorption [2] transitions, which can influence a broad range of materials properties [3][4][5]. Thus, GBs can be treated as "interfacial phases" that are thermodynamically two-dimensional (2-D) despite that they have thermodynamically-determined interfacial widths as well as through-thickness compositional and structural gradients. A new term "complexion" was introduced to differentiate such 2-D interfacial phases from the conventional bulk phases defined by Gibbs [1,3,4,6,7].Phase diagrams are one of the most useful tools for materials engineering. Materials scientists have long recognized that phase-like behaviors at GBs can often control the fabrication processing, microstructural evolution, and materials properties [3,[6][7][8][9][10][11][12]. Thus, a potentially-transformative research is represented by the development of GB "phase" (a.k.a. complexion) diagrams as an extension to bulk phase diagrams and a generally-useful materials science tool. To support this goal, recent studies [9,10,13-16] have extended bulk CALPHAD (CALculation of PHAse Diagrams) methods to model coupled GB premelting and prewetting (a.k.a. the formation of nanoscale, impurity-based, quasi-liquid complexions) and subsequently constructed a class of "GB λ diagrams" to represent the thermodynamic tendency for general GBs to disorder at high temperatures. Although the predicted trends have been validated with direct high-resolution transmission electron microscopy (HRTEM) [9,[14][15][16][17][18][19] and proven useful for forecasting sintering behaviors [9,10,[13][14][15]20], these GB λ diagrams are not yet rigorous GB complexion diagrams with well-defined transition lines. An early report in 1999 [21] also constructed a GB complexion diagram for Cu-Bi via a rather simple model that considered GBs as "quasi-liquid layers" to explain the GB segregation behaviors measured by Auger electron spectroscopy (AES), but more recent aberration-corrected scanning transmission electron microscopy (AC STEM) observed an ordered bilayer complexion in Cu-Bi instead [22]. GB complexion diagrams with first-order transition lines and critical points have been constructed using diffuse-interface (phase-field) [1,23,24] and latticetype [16,[25][26]...

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“…5. However, the treatment [14] is incorrect. It is based on a wrong solution of the convolution integral in AES [11] by setting the intensity (or "effective quantity") of each layer equal to the summary concentration of that and all following layers.…”

Section: Reliability Of Quantified Aes Datamentioning

confidence: 99%

Quantitative AES at Interfaces

Lejček¹,

Hofmann

2011

JSA

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Chemical composition of internal interfaces and especially grain boundaries differs from that of the grain interior and controls materials behavior. Application of the mostly spread method of surface analysis -Auger electron spectroscopy (AES) -for measurement of nanochemistry at these buried surfaces is complicated by necessity to open the boundary by intergranular brittle fracture. Consequently, the quantification of AES spectra must also take into account redistribution of the species, segregated at the boundary, between the two fracture surfaces. In this contribution, we analyze the transformation of AES spectra onto grain boundary concentrations using the standardless methods, which are reliable for determination of thermodynamic parameters characterizing the grain boundary segregation.

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Anisotropy of segregation at grain boundaries and surfaces

Cited by 159 publications

References 68 publications

Effect of Annealing on Microstructure, Grain Growth and Hardness of Nanocrystalline Cu-Zr Alloy Prepared by Cryogenic Ball Milling

Effect of Annealing on Microstructure, Grain Growth and Hardness of Nanocrystalline Cu-Zr Alloy Prepared by Cryogenic Ball Milling

Calculation and validation of a grain boundary complexion diagram for Bi-doped Ni

Quantitative AES at Interfaces

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