Dear Colleagues,

At the beginning of the 21st century, electronic-structure theory has matured to a degree that allows for accurate phase prediction and computational characterization of various kinds of materials; in particular, elemental metals adopting whatever allotropic structure, various intermetallic compounds, and other complex metal-rich phases. Hence, fundamental theoretical progress has been made and is rapidly continuing in both physics and chemistry. From a more applied, engineering-like perspective, there is an urgent need for novel metallic structural materials, such as advanced steels, for future challenges arising in both mechanical and civil engineering as well as energy production and conversion. While it is clear that different microstructural features influence the macroscopic behavior, modern techniques for simulation and modeling of metals and intermetallic phases at the atomic scale may enormously accelerate and guide the entire development process. In particular, atomistic understanding is a key issue because it allows for the generation of (spin-dependent) structural models of crystalline phases and the calculation of enthalpies and other free energies as a function of pressure and temperature. In combination with evolutionary algorithms and advanced thermochemical and phase-field approaches, these methods provide a solid ground for a novel methodological approach to the physics, chemistry, and engineering of metals and metal-rich materials. Furthermore, fundamental insights obtained in this manner may be incorporated, either as input parameters or key assumptions, into larger scale models, whether purely theoretical or computational, rendering atomistic simulations essential for the development of multiscale approaches. Thus, this Special Issue focusing on first-principles approaches to metals, alloys, and metallic compounds tries to follow that train of thought, and it also aims at allowing for a wider perspective on metallic materials, to be studied by physicists, chemists and materials scientists, as well as engineers.

Prof. Dr. Richard Dronskowski
Guest Editor

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Editorial

Jump to: Research

3 pages, 146 KiB  

Open AccessEditorial

First-Principles Approaches to Metals, Alloys, and Metallic Compounds

by Richard Dronskowski

Metals 2018, 8(9), 705; https://doi.org/10.3390/met8090705 - 07 Sep 2018

Cited by 1 | Viewed by 2237

Abstract

At the beginning of the 21st century, electronic-structure theory has matured to a degree that allows for accurate phase prediction and computational characterization of various kinds of materials; in particular, elemental metals adopting whatever allotropic structure, various intermetallic compounds, and other complex metal-rich [...] Read more.

At the beginning of the 21st century, electronic-structure theory has matured to a degree that allows for accurate phase prediction and computational characterization of various kinds of materials; in particular, elemental metals adopting whatever allotropic structure, various intermetallic compounds, and other complex metal-rich phases. [...] Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

Research

Jump to: Editorial

10 pages, 2542 KiB  

Open AccessArticle

Stability, Electronic Structure, and Dehydrogenation Properties of Pristine and Doped 2D MgH₂ by the First Principles Study

by Xu Gong and Xiaohong Shao

Metals 2018, 8(7), 482; https://doi.org/10.3390/met8070482 - 25 Jun 2018

Cited by 5 | Viewed by 2882

Abstract

Based on first principles calculations, we theoretically predict the new two-dimensional (2D) MgH₂. The thermodynamic stability, partial density of states, electron localization function, and Bader charge of pure and the transition metal (Ti, V, and Mn) doped 2D MgH₂ are [...] Read more.

Based on first principles calculations, we theoretically predict the new two-dimensional (2D) MgH₂. The thermodynamic stability, partial density of states, electron localization function, and Bader charge of pure and the transition metal (Ti, V, and Mn) doped 2D MgH₂ are investigated. The results show that all the systems are dynamically stable, and the dehydrogenation properties indicate that the decomposition temperature can be reduced by introducing the transition metal, and the Mn doped system exhibits good performance for better hydrogen storage and dehydrogenation kinetics. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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16 pages, 1350 KiB  

Open AccessArticle

Multiscale Modelling of Hydrogen Transport and Segregation in Polycrystalline Steels

by Claas Hüter, Pratheek Shanthraj, Eunan McEniry, Robert Spatschek, Tilmann Hickel, Ali Tehranchi, Xiaofei Guo and Franz Roters

Metals 2018, 8(6), 430; https://doi.org/10.3390/met8060430 - 07 Jun 2018

Cited by 22 | Viewed by 5226

Abstract

A key issue in understanding and effectively managing hydrogen embrittlement in complex alloys is identifying and exploiting the critical role of the various defects involved. A chemo-mechanical model for hydrogen diffusion is developed taking into account stress gradients in the material, as well [...] Read more.

A key issue in understanding and effectively managing hydrogen embrittlement in complex alloys is identifying and exploiting the critical role of the various defects involved. A chemo-mechanical model for hydrogen diffusion is developed taking into account stress gradients in the material, as well as microstructural trapping sites such as grain boundaries and dislocations. In particular, the energetic parameters used in this coupled approach are determined from ab initio calculations. Complementary experimental investigations that are presented show that a numerical approach capable of massive scale-bridging up to the macroscale is required. Due to the wide range of length scales accounted for, we apply homogenisation schemes for the hydrogen concentration to reach simulation dimensions comparable to metallurgical process scales. Via a representative volume element approach, an ab initio based scale bridging description of dislocation-induced hydrogen aggregation is easily accessible. When we extend the representative volume approach to also include an analytical approximation for the ab initio based description of grain boundaries, we find conceptual limitations that hinder a quantitative comparison to experimental data in the current stage. Based on this understanding, the development of improved strategies for further efficient scale bridging approaches is foreseen. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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12 pages, 2284 KiB  

Open AccessArticle

Ab Initio Guided Low Temperature Synthesis Strategy for Smooth Face–Centred Cubic FeMn Thin Films

by Friederike Herrig, Denis Music, Bernhard Völker, Marcus Hans, Peter J. Pöllmann, Anna L. Ravensburg and Jochen M. Schneider

Metals 2018, 8(6), 384; https://doi.org/10.3390/met8060384 - 26 May 2018

Cited by 8 | Viewed by 4382

Abstract

The sputter deposition of FeMn thin films with thicknesses in the range of hundred nanometres and beyond requires relatively high growth temperatures for the formation of the face-centred cubic (fcc) phase, which results in high thin film roughness. A low temperature [...] Read more.

The sputter deposition of FeMn thin films with thicknesses in the range of hundred nanometres and beyond requires relatively high growth temperatures for the formation of the face-centred cubic (fcc) phase, which results in high thin film roughness. A low temperature synthesis strategy, based on local epitaxial growth of a 100 nm thick fcc FeMn film as well as a Cu nucleation layer on an α-Al₂O₃ substrate at 160 °C, enables roughness values (R_a) as low as ~0.6 nm, which is in the same order of magnitude as the pristine substrate (~0.1 nm). The synthesis strategy is guided by ab initio calculations, indicating very strong interfacial bonding of the Cu nucleation layer to an α-Al₂O₃ substrate (work of separation 5.48 J/m²)—which can be understood based on the high Cu coordination at the interface—and between fcc FeMn and Cu (3.45 J/m²). Accompanied by small lattice misfits between these structures, the strong interfacial bonding is proposed to enable the local epitaxial growth of a smooth fcc FeMn thin film. Based on the here introduced synthesis strategy, the implementation of fcc FeMn based thin film model systems for materials with interface dominated properties such as FeMn steels containing κ-carbide precipitates or secondary phases appears meaningful. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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29 pages, 2730 KiB  

Open AccessArticle

Modeling of Phase Equilibria in Ni-H: Bridging the Atomistic with the Continuum Scale

by Dominique Korbmacher, Johann Von Pezold, Steffen Brinckmann, Jörg Neugebauer, Claas Hüter and Robert Spatschek

Metals 2018, 8(4), 280; https://doi.org/10.3390/met8040280 - 18 Apr 2018

Cited by 4 | Viewed by 3708

Abstract

In this paper, we present a model which allows bridging the atomistic description of two-phase systems to the continuum level, using Ni-H as a model system. Considering configurational entropy, an attractive hydrogen–hydrogen interaction, mechanical deformations and interfacial effects, we obtained a fully quantitative [...] Read more.

In this paper, we present a model which allows bridging the atomistic description of two-phase systems to the continuum level, using Ni-H as a model system. Considering configurational entropy, an attractive hydrogen–hydrogen interaction, mechanical deformations and interfacial effects, we obtained a fully quantitative agreement in the chemical potential, without the need for any additional adjustable parameter. We find that nonlinear elastic effects are crucial for a complete understanding of constant volume phase coexistence, and predict the phase diagram with and without elastic effects. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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15 pages, 348 KiB  

Open AccessArticle

Linking Ab Initio Data on Hydrogen and Carbon in Steel to Statistical and Continuum Descriptions

by Marc Weikamp, Claas Hüter and Robert Spatschek

Metals 2018, 8(4), 219; https://doi.org/10.3390/met8040219 - 27 Mar 2018

Cited by 6 | Viewed by 3374

Abstract

We present a selection of scale transfer approaches from the electronic to the continuum regime for topics relevant to hydrogen embrittlement. With a focus on grain boundary related hydrogen embrittlement, we discuss the scale transfer for the dependence of the carbon solution behavior [...] Read more.

We present a selection of scale transfer approaches from the electronic to the continuum regime for topics relevant to hydrogen embrittlement. With a focus on grain boundary related hydrogen embrittlement, we discuss the scale transfer for the dependence of the carbon solution behavior in steel on elastic effects and the hydrogen solution in austenitic bulk regions depending on Al content. We introduce an approximative scheme to estimate grain boundary energies for varying carbon and hydrogen population. We employ this approach for a discussion of the suppressing influence of Al on the substitution of carbon with hydrogen at grain boundaries, which is an assumed mechanism for grain boundary hydrogen embrittlement. Finally, we discuss the dependence of hydride formation on the grain boundary stiffness. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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16 pages, 4233 KiB  

Open AccessFeature PaperArticle

On the Mn–C Short-Range Ordering in a High-Strength High-Ductility Steel: Small Angle Neutron Scattering and Ab Initio Investigation

by Wenwen Song, Dimitri Bogdanovski, Ahmet Bahadir Yildiz, Judith E. Houston, Richard Dronskowski and Wolfgang Bleck

Metals 2018, 8(1), 44; https://doi.org/10.3390/met8010044 - 10 Jan 2018

Cited by 21 | Viewed by 6109

Abstract

The formation of Mn–C short-range ordering (SRO) has a great influence on the mechanical properties of high-Mn steels. In the present work, the formation of Mn–C SRO during recrystallization of an X60Mn18 steel was investigated by means of a combined study employing small [...] Read more.

The formation of Mn–C short-range ordering (SRO) has a great influence on the mechanical properties of high-Mn steels. In the present work, the formation of Mn–C SRO during recrystallization of an X60Mn18 steel was investigated by means of a combined study employing small angle neutron scattering (SANS) and ab initio ground-state energy calculations based on density-functional theory. The SANS measurements prove the presence of Mn–C SRO in the recrystallization annealed X60Mn18 steel and indicate the evolution of the SRO during recrystallization. The results show that with the increase in annealing time, the mean size of the Mn–C SRO decreases, whereas the number density increases. The ab initio calculations well describe the energetically favored condition of Mn–C SRO and provide the theoretical explanation of the clustering formation and evolution in the X60Mn18 steel. The stress-strain curve of the X60Mn18 steel exhibits a high strain-hardening rate and the plastic deformation is characterized with a series of serrations during a uniaxial tensile test. In the end, the correlation between Mn–C SRO and the serrated flow of high-Mn steels is further discussed. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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15 pages, 2283 KiB  

Open AccessArticle

Ab Initio-Based Modelling of the Yield Strength in High-Manganese Steels

by Simon Sevsek and Wolfgang Bleck

Metals 2018, 8(1), 34; https://doi.org/10.3390/met8010034 - 05 Jan 2018

Cited by 12 | Viewed by 4332

Abstract

An ab initio-based model for the strength increase by short-range ordering of C-Mn-Al clusters has been developed. The model is based on ab initio calculations of ordering energies. The impact of clusters on the yield strength of high-manganese austenitic steels (HMnS) is highly [...] Read more.

An ab initio-based model for the strength increase by short-range ordering of C-Mn-Al clusters has been developed. The model is based on ab initio calculations of ordering energies. The impact of clusters on the yield strength of high-manganese austenitic steels (HMnS) is highly dependent on the configurational structure of the cells that carbon atoms will position themselves as interstitial atoms. The impact of the alloying elements C, Mn, and Al on the potential and actual increase in yield strength is analyzed. A model for the calculation of yield strengths of HMnS is derived that includes the impact of short-range ordering, grain size refinement, and solid solution strengthening. The model is in good agreement with experimental data and performs better than other models that do not include strengthening by short-range ordering. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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19547 KiB  

Open AccessArticle

Molecular Dynamics Simulation of Crack Propagation in Nanoscale Polycrystal Nickel Based on Different Strain Rates

by Yanqiu Zhang and Shuyong Jiang

Metals 2017, 7(10), 432; https://doi.org/10.3390/met7100432 - 16 Oct 2017

Cited by 14 | Viewed by 6380

Abstract

Based on the strain rates of 2 × 108 s−1 and 2 × 1010 s−1, molecular dynamics simulation was conducted so as to study mechanisms of crack propagation in nanoscale polycrystal nickel. The strain rate has an important effect on the mechanism of [...] Read more.

Based on the strain rates of 2 × 108 s−1 and 2 × 1010 s−1, molecular dynamics simulation was conducted so as to study mechanisms of crack propagation in nanoscale polycrystal nickel. The strain rate has an important effect on the mechanism of crack propagation in nanoscale polycrystal nickel. In the case of a higher strain rate, local non-3D-crystalline atoms are induced and Lomer-Cottrell locks are formed, which plays a critical role in crack initiation and propagation. Orientation difference between adjacent grains leads to the slipping of dislocations along the different directions, which results in the initiation of a void near the triple junction of grain boundaries and further contributes to accelerating the crack propagation. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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1897 KiB  

Open AccessArticle

First-Principles Investigation of Structural, Electronic and Elastic Properties of HfX (X = Os, Ir and Pt) Compounds

by Xianfeng Li, Cunjuan Xia, Mingliang Wang, Yi Wu and Dong Chen

Metals 2017, 7(8), 317; https://doi.org/10.3390/met7080317 - 18 Aug 2017

Cited by 11 | Viewed by 4216

Abstract

The structural, electronic and elastic properties of B2 structure Hafnium compounds were investigated by means of first-principles calculations based on the density functional theory within generalized gradient approximation (GGA) and local density approximation (LDA) methods. Both GGA and LDA methods can make acceptable [...] Read more.

The structural, electronic and elastic properties of B2 structure Hafnium compounds were investigated by means of first-principles calculations based on the density functional theory within generalized gradient approximation (GGA) and local density approximation (LDA) methods. Both GGA and LDA methods can make acceptable optimized lattice parameters in comparison with experimental parameters. Therefore, both GGA and LDA methods are used to predict the electronic and elastic properties of B2 HfX (X = Os, Ir and Pt) compounds. Initially, the calculated formation enthalpies have confirmed the order of thermodynamic stability as HfPt > HfIr > HfOs. Secondly, the electronic structures are analyzed to explain the bonding characters and stabilities in these compounds. Furthermore, the calculated elastic properties and elastic anisotropic behaviors are ordered and analyzed in these compounds. The calculated bulk moduli are in the reduced order of HfOs > HfIr > HfPt, which has exhibited the linear relationship with electron densities. Finally, the anisotropy of acoustic velocities, Debye temperatures and thermal conductivities are obtained and discussed. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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886 KiB  

Open AccessArticle

Transition of the Interface between Iron and Carbide Precipitate From Coherent to Semi-Coherent

by Hideaki Sawada, Shunsuke Taniguchi, Kazuto Kawakami and Taisuke Ozaki

Metals 2017, 7(7), 277; https://doi.org/10.3390/met7070277 - 19 Jul 2017

Cited by 20 | Viewed by 5902

Abstract

There are some precipitates that undergo transition from a coherent to semi-coherent state during growth. An example of such a precipitate in steel is carbide with a NaCl-type structure, such as TiC and NbC. The interface energy between carbide precipitate and iron is [...] Read more.

There are some precipitates that undergo transition from a coherent to semi-coherent state during growth. An example of such a precipitate in steel is carbide with a NaCl-type structure, such as TiC and NbC. The interface energy between carbide precipitate and iron is obtained via large-scale first-principles electronic structure calculation. The strain energy is estimated by structure optimization of the iron matrix with virtual carbide precipitate using the empirical potential. The transition of the interface from a coherent to semi-coherent state was examined by comparing the interface and strain energies between the coherent and semi-coherent interfaces. The sizes where both the precipitates undergo this transition are smaller than those of the interfaces with minimum misfit. The estimated transition diameter of TiC is in agreement with the experimentally obtained value. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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3409 KiB  

Open AccessFeature PaperArticle

The Role of κ-Carbides as Hydrogen Traps in High-Mn Steels

by Tobias A. Timmerscheidt, Poulumi Dey, Dimitri Bogdanovski, Jörg Von Appen, Tilmann Hickel, Jörg Neugebauer and Richard Dronskowski

Metals 2017, 7(7), 264; https://doi.org/10.3390/met7070264 - 11 Jul 2017

Cited by 32 | Viewed by 6628

Abstract

Since the addition of Al to high-Mn steels is known to reduce their sensitivity to hydrogen-induced delayed fracture, we investigate possible trapping effects connected to the presence of Al in the grain interior employing density-functional theory (DFT). The role of Al-based precipitates is [...] Read more.

Since the addition of Al to high-Mn steels is known to reduce their sensitivity to hydrogen-induced delayed fracture, we investigate possible trapping effects connected to the presence of Al in the grain interior employing density-functional theory (DFT). The role of Al-based precipitates is also investigated to understand the relevance of short-range ordering effects. So-called E2₁-Fe₃AlC κ-carbides are frequently observed in Fe-Mn-Al-C alloys. Since H tends to occupy the same positions as C in these precipitates, the interaction and competition between both interstitials is also investigated via DFT-based simulations. While the individual H–H/C–H chemical interactions are generally repulsive, the tendency of interstitials to increase the lattice parameter can yield a net increase of the trapping capability. An increased Mn content is shown to enhance H trapping due to attractive short-range interactions. Favorable short-range ordering is expected to occur at the interface between an Fe matrix and the E2₁-Fe₃AlC κ-carbides, which is identified as a particularly attractive trapping site for H. At the same time, accumulation of H at sites of this type is observed to yield decohesion of this interface, thereby promoting fracture formation. The interplay of these effects, evident in the trapping energies at various locations and dependent on the H concentration, can be expressed mathematically, resulting in a term that describes the hydrogen embrittlement. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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