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Grain Boundary Segregation and Related Phenomena in Metals and Alloys

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Advanced Materials Characterization".

Deadline for manuscript submissions: closed (30 November 2019) | Viewed by 23015

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Special Issue Editor

Dr. Václav Paidar

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Guest Editor

Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, CZ-182 21 Prague 8, Czech Republic
Interests: Extended crystal defects; dislocations and grain boundaries; metals and intermetallics

Special Issue Information

Dear Colleagues,

Grain boundary segregation has a large impact on grain boundary properties. Certain solute atoms can concentrate at the boundaries and drastically change various material properties.

After the introduction of structural units for the description of grain boundary structures in the second half of the last century, interface chemistry has achieved an important development both due to new theoretical models and improved experimental techniques.

The aim of this Special Issue is to demonstrate recent progress including new concepts regarding the grain boundary complexions considered for the transformation of two-dimensional interfacial structures and summarized reliable experimental results that are also essential for material technological applications.

The research in this field covers materials design via grain boundary engineering, the stabilization of nanocrystalline structures, and nonequilibrium phenomena due to irradiation, to mention only a few special cases.

Dr. Václav Paidar
Guest Editor

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Keywords

Segregation to well-defined grain boundaries in bicrystals
Experimental techniques to measure segregation to solid/solid interfaces
Calculations of grain boundary atomic structures containing solute atoms
Material properties influenced by grain boundary segregation

Published Papers (7 papers)

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Research

8 pages, 4278 KiB

Open AccessArticle

Role of Impurity Sulphur in the Ductility Trough of Austenitic Iron–Nickel Alloys

by Frédéric Christien

Materials 2020, 13(3), 539; https://doi.org/10.3390/ma13030539 - 23 Jan 2020

Cited by 10 | Viewed by 2178

Abstract

The role of impurity sulphur in the ductility trough of iron–nickel (Fe–Ni) alloys is investigated using hot tensile tests. A strong detrimental effect of some ppm levels of sulphur is demonstrated. In addition, it is shown that, in the ductility trough, material failure occurs through subcritical grain boundary crack propagation, involving dynamic embrittlement at the crack tip, due to the sulphur. Very high intergranular crack growth rates are observed. This is possible because plastic deformation accelerates the transport of sulphur to the crack tip, by several orders of magnitude, compared to normal bulk diffusion. The ductility is recovered at high strain rates, which correlates with a decrease in the sulphur concentration measured on the fracture surface. It is suggested that the main mechanism of sulphur transport is dragging by moving dislocations. Full article

(This article belongs to the Special Issue Grain Boundary Segregation and Related Phenomena in Metals and Alloys)

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Figure 1

14 pages, 851 KiB

Open AccessArticle

Partitioning of Interstitial Segregants during Decohesion: A DFT Case Study of the Σ3 Symmetric Tilt Grain Boundary in Ferritic Steel

by Xiang Huang and Rebecca Janisch

Materials 2019, 12(18), 2971; https://doi.org/10.3390/ma12182971 - 13 Sep 2019

Cited by 4 | Viewed by 2664

Abstract

The effect of hydrogen atoms at grain boundaries in metals is usually detrimental to the cohesion of the interface. This effect can be quantified in terms of the strengthening energy, which is obtained following the thermodynamic model of Rice and Wang. A critical component of this model is the bonding or solution energy of the atoms to the free surfaces that are created during decohesion. At a grain boundary in a multicomponent system, it is not immediately clear how the different species would partition and distribute on the cleaved free surfaces. In this work, it is demonstrated that the choice of partitioning pattern has a significant effect on the predicted influence of H and C on grain boundary cohesion. To this end, the

Σ 3 (112) [1 \bar{1} 0]

symmetric tilt grain boundary in bcc Fe with different contents of interstitial C and H was studied, taking into account all possible distributions of the elements, as well as surface diffusion effects. H as a single element has a negative influence on grain boundary cohesion, independent of the details of the H distribution. C, on the other hand, can act both ways, enhancing or reducing the cohesion of the interface. The effect of mixed H and C compositions depends on the partition pattern. However, the general trend is that the number of detrimental cases increases with increasing H content. A decomposition of the strengthening energy into chemical and mechanical contributions shows that the elastic contribution dominates at high C contents, while the chemical contribution sets the trend for high H contents. Full article

(This article belongs to the Special Issue Grain Boundary Segregation and Related Phenomena in Metals and Alloys)

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Graphical abstract

22 pages, 11130 KiB

Open AccessArticle

Diffusive Steel Scrap Melting in Carbon-Saturated Hot Metal—Phenomenological Investigation at the Solid–Liquid Interface

by Florian Markus Penz, Johannes Schenk, Rainer Ammer, Gerald Klösch, Krzysztof Pastucha and Michael Reischl

Materials 2019, 12(8), 1358; https://doi.org/10.3390/ma12081358 - 25 Apr 2019

Cited by 14 | Viewed by 3910

Abstract

The oxygen steelmaking process in a Linz-Donawitz (LD) converter is responsible for more than 70% of annual crude steel production. Optimization of the process control and numerical simulation of the LD converter are some of the current challenges in ferrous metallurgical research. Because of the process conditions and oxidation of impurities of the hot metal, a lot of chemical heat is generated. Therefore, steel scrap is charged as a coolant with the economical side aspect of its recycling. One of the more complex aspects is, among others, the dissolution and melting behaviour of the scrap in carbon-saturated hot metal. Heat and mass transfer act simultaneously, which has already been investigated by several researchers using different experimental approaches. The appearances at the interface between solid steel and liquid hot metal during diffusive scrap melting have been described theoretically but never investigated in detail. After an experimental investigation under natural and forced convective conditions, the samples were further investigated with optical microscopy and electron probe microanalysis (EPMA). A steep carbon concentration gradient in the liquid appeared, which started at an interface carbon concentration equal to the concentration on the solid side of the interface. Moreover, the boundary layer thickness moved towards zero, which symbolized that the boundary layer theory based on thermodynamic equilibrium was not valid. This fact was concluded through the prevailing dynamic conditions formed by natural and forced convection. Full article

(This article belongs to the Special Issue Grain Boundary Segregation and Related Phenomena in Metals and Alloys)

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Graphical abstract

7 pages, 2229 KiB

Open AccessArticle

Effect of Micro-Steps on Twinning and Interfacial Segregation in Mg-Ag Alloy

by Yi Liu, Xuefei Chen, Kang Wei, Lirong Xiao, Bin Chen, Haibo Long, Yandong Yu, Zhaohua Hu and Hao Zhou

Materials 2019, 12(8), 1307; https://doi.org/10.3390/ma12081307 - 22 Apr 2019

Cited by 13 | Viewed by 3545

Abstract

Twinning structures and their interfacial segregation play a key role in strengthening of magnesium alloys. Micro-steps are frequently existed in the incoherent twin boundaries, while the effect of them on interface and interfacial segregation is still not clear. In this work, we performed an atomic-scale microstructure analysis using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) to explore the effect of micro-steps on twin and its interfacial segregation in Mg-Ag alloy. Diffraction pattern of the incoherent {10

\bar{1}

1} twin shows that the misorientation has a slight tilt of 5° from its theoretical angle of 125° due to the accumulated effects of the micro-steps and their misfit dislocations in twin boundaries. Most of the micro-steps in {10

\bar{1}

1} twin boundary are in the height of 2

d_{(10 \bar{1} 1)}

and 4

d_{(10 \bar{1} 1)}

, respectively, and both of them have two types according to whether there are dislocations on the micro-steps. The twin boundary is interrupted by many micro-steps, which leads to a step-line distributed interfacial segregation. Moreover, the Ag tends to segregate to dislocation cores, which results in the interruption of interfacial segregation at the micro-steps with dislocations. Full article

(This article belongs to the Special Issue Grain Boundary Segregation and Related Phenomena in Metals and Alloys)

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9 pages, 1653 KiB

Open AccessArticle

The Significance of Entropy in Grain Boundary Segregation

by Pavel Lejček, Siegfried Hofmann and Václav Paidar

Materials 2019, 12(3), 492; https://doi.org/10.3390/ma12030492 - 05 Feb 2019

Cited by 14 | Viewed by 2895

Abstract

The role of entropy in materials science is demonstrated in this report in order to establish its importance for the example of solute segregation at the grain boundaries of bcc iron. We show that substantial differences in grain boundary chemistry arise if their composition is calculated with or without consideration of the entropic term. Another example which clearly documents the necessity of implementing the entropic term in materials science is the enthalpy-entropy compensation effect. Entropy also plays a decisive role in the anisotropy of grain boundary segregation and in interface characterization. The consequences of the ambiguous determination of grain boundary segregation on the prediction of materials behavior are also briefly discussed. All the mentioned examples prove the importance of entropy in the quantification of grain boundary segregation and consequently of other materials properties. Full article

(This article belongs to the Special Issue Grain Boundary Segregation and Related Phenomena in Metals and Alloys)

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17 pages, 3437 KiB

Open AccessArticle

An Ab Initio Study of Connections between Tensorial Elastic Properties and Chemical Bonds in Σ5(210) Grain Boundaries in Ni₃Si

by Martin Friák, Martin Zelený, Monika Všianská, David Holec and Mojmír Šob

Materials 2018, 11(11), 2263; https://doi.org/10.3390/ma11112263 - 13 Nov 2018

Cited by 4 | Viewed by 3365

Abstract

Using quantum-mechanical methods we calculate and analyze (tensorial) anisotropic elastic properties of the ground-state configurations of interface states associated with

Σ

5(210) grain boundaries (GBs) in cubic L1

_{2}

-structure Ni

_{3}

Si. We assess the mechanical stability of interface states with two [...] Read more.

Using quantum-mechanical methods we calculate and analyze (tensorial) anisotropic elastic properties of the ground-state configurations of interface states associated with

Σ

5(210) grain boundaries (GBs) in cubic L1

_{2}

-structure Ni

_{3}

Si. We assess the mechanical stability of interface states with two different chemical compositions at the studied GB by checking rigorous elasticity-based Born stability criteria. In particular, we show that a GB variant containing both Ni and Si atoms at the interface is unstable with respect to shear deformation (one of the elastic constants,

C_{55}

, is negative). This instability is found for a rectangular-parallelepiped supercell obtained when applying standard coincidence-lattice construction. Our elastic-constant analysis allowed us to identify a shear-deformation mode reducing the energy and, eventually, to obtain mechanically stable ground-state characterized by a shear-deformed parallelepiped supercell. Alternatively, we tested a stabilization of this GB interface state by Al substituents replacing Si atoms at the GB. We further discuss an atomistic origin of this instability in terms of the crystal orbital Hamilton population (COHP) and phonon dispersion calculations. We find that the unstable GB variant shows a very strong interaction between the Si atoms in the GB plane and Ni atoms in the 3rd plane off the GB interface. However, such bond reinforcement results in weakening of interaction between the Ni atoms in the 3rd plane and the Si atoms in the 5th plane making this GB variant mechanically unstable. Full article

(This article belongs to the Special Issue Grain Boundary Segregation and Related Phenomena in Metals and Alloys)

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14 pages, 5464 KiB

Open AccessArticle

Effect of Electropulsing Treatment on the Fatigue Crack Growth Behavior of Copper

by Yan Yin, Haibo Chen, Yasuyuki Morita, Yuhki Toku and Yang Ju

Materials 2018, 11(11), 2168; https://doi.org/10.3390/ma11112168 - 02 Nov 2018

Cited by 4 | Viewed by 3227

Abstract

Crack propagation was quantitatively evaluated to investigate the effect of electropulsing treatment (EPT) on fatigue crack growth of copper specimens. Varying fatigue cycles were obtained under six different load levels. The crack lengths were measured under two load levels to examine the effect of cyclic stress. The microhardness was measured around the vicinity of the crack tip. Furthermore, the fracture surface was observed by scanning electron microscopy. Results show that EPT with electric current density of 150 A/mm² enhances the high-cycle fatigue life, and the effect tends to increase with the decrease in cyclic stress. Vickers microhardness (HV) near the crack tip decreases to normal levels after treatment, and the approaching cracks on two sides can be observed. Local annealing and recrystallization occur around the fatigue crack tip. Accordingly, crack propagation can be delayed, and fatigue life can be prolonged by EPT. Full article

(This article belongs to the Special Issue Grain Boundary Segregation and Related Phenomena in Metals and Alloys)

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