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Peter Klaver

Delft University of Technology, Materials Science and Engineering, Post-Doc

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I did my MSc and PhD (2000-2004) in Materials Science at Delft University in the Netherlands, both on molecular dynamics simulations of physical vapour deposition of thin metal films. As part of my PhD I also learned to do DFT. That was my main research tool during the two postdoc jobs on radiation damage in nuclear Fe alloys that I did after my PhD, in Belfast and Edinburgh. After my postdoc job in Edinburgh I moved back to Delft University, where I embarked on a long series of postdoc contracts, which I plan to continue until I retire (I prefer to stick to the postdoc working week where you spend most time on hands on research). The postdoc jobs have been on a variety of different subjects, including again many on nuclear alloys but also atomistic simulation of ionic liquids interacting with solid surfaces, FeZnAl intermetallics (for Ruhr Universität Bochum, Germany, working from Delft), and graphene on Cu surfaces. From 2014 to 2016 I did a postdoc at the DIFFER institute in Eindhoven, looking a W surfaces exposed to plasma, among other things. After the job at DIFFER it was postdoc jobs in Delft again, using CALPHAD databases to look at phase stability of high entropy alloys and then nuclear alloys again. The latter job was extended by a short postdoc contract working for the University of Lille.
Supervisors: Dr. S. E. Offerman and Dr. M. H. F. Sluiter
Phone: +31 (0)71 7514774
Address: room H-4-290
Dept. of Materials Science and Engineering,
TU Delft, Faculty of 3mE (building 34)
Mekelweg 2, 2628 CD Delft
Netherlands

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Papers by Peter Klaver

Sessile ⟨100⟩ self-interstitial clusters with non-parallel edge dumbbells in irradiated bcc Fe and other metals

Scripta Materialia

Density Functional Theory calculations of self-interstitial atom clusters in bcc Fe unexpectedly ... more Density Functional Theory calculations of self-interstitial atom clusters in bcc Fe unexpectedly show that from ~9-14 self-interstitial atoms, an intriguing new family of sessile ⟨100⟩ clusters, surrounded by ⟨110⟩ dumbbells, are more stable than highly mobile clusters of parallel ⟨111⟩ dumbbells. The ⟨110⟩ edge dumbbells find a favorable location in terms of strain energy on the tensile side around the edges of the ⟨100⟩ center, thus stabilizing the clusters. These sessile clusters might explain resistivity recovery results that suggested an absence of glissile self-interstitial clusters up to large cluster sizes in irradiated Fe, while smaller self-interstitial atom clusters likely would have been present. The mechanism of non-parallel edge interstitials stabilizing an otherwise higher energy interstitial loop is also found in some fcc metals.

The effect of Cr concentration on single interstitials stability in FeCr alloys

Oxygen Evolution at Hematite Surfaces: The Impact of Structure and Oxygen Vacancies on Lowering the Overpotential

Journal of Physical Chemistry C, Aug 5, 2016

A molecular dynamics study of ion beam assisted deposition of thin molybdenum films and analysis by thermal desorption spectrometry

Cu/Ta and Ta/Cu thin film growth, studied by Molecular Dynamics simulations

Journal of Computer-aided Materials Design, 2003

The Computational Modeling of Alloys: From Ab Initio and Thermodynamics to Radiation-Induced Heterogeneous Precipitation

Journal: Materials, Apr 1, 2007

Machine learning–enabled high-entropy alloy discovery

Science

High-entropy alloys are solid solutions of multiple principal elements that are capable of reachi... more High-entropy alloys are solid solutions of multiple principal elements that are capable of reaching composition and property regimes inaccessible for dilute materials. Discovering those with valuable properties, however, too often relies on serendipity, because thermodynamic alloy design rules alone often fail in high-dimensional composition spaces. We propose an active learning strategy to accelerate the design of high-entropy Invar alloys in a practically infinite compositional space based on very sparse data. Our approach works as a closed-loop, integrating machine learning with density-functional theory, thermodynamic calculations, and experiments. After processing and characterizing 17 new alloys out of millions of possible compositions, we identified two high-entropy Invar alloys with extremely low thermal expansion coefficients around 2 × 10 −6 per degree kelvin at 300 kelvin. We believe this to be a suitable pathway for the fast and automated discovery of high-entropy alloys...

Machine learning-enabled high-entropy alloy discovery

Science, 2022

High-entropy alloys are solid solutions of multiple principal elements that are capable of reachi... more High-entropy alloys are solid solutions of multiple principal elements that are capable of reaching composition and property regimes inaccessible for dilute materials. Discovering those with valuable properties, however, too often relies on serendipity, because thermodynamic alloy design rules alone often fail in high-dimensional composition spaces. We propose an active learning strategy to accelerate the design of high-entropy Invar alloys in a practically infinite compositional space based on very sparse data. Our approach works as a closed-loop, integrating machine learning with density-functional theory, thermodynamic calculations, and experiments. After processing and characterizing 17 new alloys out of millions of possible compositions, we identified two high-entropy Invar alloys with extremely low thermal expansion coefficients around 2 × 10 −6 per degree kelvin at 300 kelvin. We believe this to be a suitable pathway for the fast and automated discovery of high-entropy alloys with optimal thermal, magnetic, and electrical properties.

Defect and solute properties in dilute Fe-Cr-Ni austenitic alloys from first principles

We present results of an extensive set of first-principles density functional theory calculations... more

High entropy alloys towards industrial applications: High-throughput screening and experimental investigation

Materials Science and Engineering: A, 2022

Using the Thermo-Calc implementation of the CALPHAD approach, high-throughput screening of the Co... more Using the Thermo-Calc implementation of the CALPHAD approach, high-throughput screening of the Co-Cr-Fe-Mn-Ni system was implemented to find &#39;islands&#39; of single phase FCC structure within the compositional space in order to reduce the cost of this well-studied alloy system. The screening identified a region centred around Co 10 Cr 12 Fe 43 Mn 18 Ni 17 , reducing the material cost compared to the equiatomic alloy by ~40%. The alloy was experimentally investigated at room and elevated temperatures, including in-situ tensile testing. The alloy was found to possess slightly lower strength compared to the equiatomic alloy at room temperature, however, exhibited excellent thermal strength up to 873K. Deformation twinning was observed after tensile testing at room temperature, primarily attributed to the reduced stacking fault energy (SFE), which was proven by a thermodynamic model for calculating the SFE. The softening behaviour at room temperature can be explained through solid solution hardening (SSH), whereby a modified approach to Labusch&#39;s model was used to calculate the SSH in reported alloys in this study within the Co-Cr-Fe-Mn-Ni system. The modified models for SFE and SSH are proposed to be implemented into high-throughput screening algorithms for accelerated alloy design towards specific mechanical properties.

Molecular dynamics simulations of ballistic He penetration into W fuzz

Nuclear Fusion, 2016

Brute Force Composition Scanning with a CALPHAD Database to Find Low Temperature Body Centered Cubic High Entropy Alloys

Entropy, 2018

We used the Thermo-Calc High Entropy Alloy CALPHAD database to determine the stable phases of AlC... more We used the Thermo-Calc High Entropy Alloy CALPHAD database to determine the stable phases of AlCrMnNbTiV, AlCrMoNbTiV, AlCrFeTiV and AlCrMnMoTi alloys from 800 to 2800 K. The concentrations of elements were varied from 1–49 atom%. A five- or six-dimensional grid is constructed, with stable phases calculated at each grid point. Thermo-Calc was used as a massive parallel tool and three million compositions were calculated, resulting in tens of thousands of compositions for which the alloys formed a single disordered body centered cubic (bcc) phase at 800 K. By filtering out alloy compositions for which a disordered single phase persists down to 800 K, composition ‘islands’ of high entropy alloys are determined in composition space. The sizes and shapes of such islands provide information about which element combinations have good high entropy alloy forming qualities as well as about the role of individual elements within an alloy. In most cases disordered single phases are formed mos...

MD and BCA simulations of He and H bombardment of fuzz in bcc elements

Journal of Nuclear Materials, 2017

Inconsistencies in modelling interstitials in FeCr with empirical potentials

Computational Materials Science, 2016

Molecular dynamics simulation of graphene on Cu (100) and (111) surfaces

Carbon, 2015

Defect production during ion-assisted deposition of molybdenum films studied by molecular dynamics

MRS Proceedings, 1997

ABSTRACTLow energy argon-ion assisted growth of thin molybdenum films (∼ 60 Å) has been studied b... more ABSTRACTLow energy argon-ion assisted growth of thin molybdenum films (∼ 60 Å) has been studied by molecular dynamics simulations. The effects of a single ion impact are discussed, but more particularly we consider film growth from a manufacturing viewpoint and examine the properties of the completed films. Results for ion-beam assisted deposition are compared with those for unassisted growth (i.e. physical vapor deposition). Surface morphology, defect generation, argon incorporation, and the various responsible atomic mechanisms are discussed.

First-principles study of point defects in an fcc Fe-10Ni-20Cr model alloy

Physical Review B, 2014

On the mobility of vacancy clusters in reduced activation steels: an atomistic study in the Fe–Cr–W model alloy

Journal of Physics: Condensed Matter, 2013

Reduced activation steels are considered as structural materials for future fusion reactors. Besi... more Reduced activation steels are considered as structural materials for future fusion reactors. Besides iron and the main alloying element chromium, these steels contain other minor alloying elements, typically tungsten, vanadium and tantalum. In this work we study the impact of chromium and tungsten, being major alloying elements of ferritic Fe-Cr-W-based steels, on the stability and mobility of vacancy defects, typically formed under irradiation in collision cascades. For this purpose, we perform ab initio calculations, develop a many-body interatomic potential (EAM formalism) for large-scale calculations, validate the potential and apply it using an atomistic kinetic Monte Carlo method to characterize the lifetime and diffusivity of vacancy clusters. To distinguish the role of Cr and W we perform atomistic kinetic Monte Carlo simulations in Fe-Cr, Fe-W and Fe-Cr-W alloys. Within the limitation of transferability of the potentials it is found that both Cr and W enhance the diffusivity of vacancy clusters, while only W strongly reduces their lifetime. The cluster lifetime reduction increases with W concentration and saturates at about 1-2 at.%. The obtained results imply that W acts as an efficient &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;breaker&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; of small migrating vacancy clusters and therefore the short-term annealing process of cascade debris is modified by the presence of W, even in small concentrations.

Interaction of minor alloying elements of high-Cr ferritic steels with lattice defects: An ab initio study

Journal of Nuclear Materials, 2014

Abstract Basic properties of minor alloying elements, namely Mo, W, Nb, Ta, V, Mn, Si entering th... more Abstract Basic properties of minor alloying elements, namely Mo, W, Nb, Ta, V, Mn, Si entering the conventional and reduced-activation structural Fe–(9–12)Cr steels have been analyzed using ab initio calculations. The electronic structure calculations were applied to study the interaction of minor alloying elements with a number of important and well defined lattice structures, such as point defects, the 1/2〈1 1 1〉 screw dislocation core, high angle symmetric grain boundaries and free surfaces. The studied elements were classified according to their similarities and discrepancies regarding the interaction with the above mentioned defects. The refractory alloying elements are found to follow the same trend whereas Mn and Si exhibit peculiar behavior with respect to the interaction with both point and extended lattice defects. The obtained results are discussed and compared with previously published ab initio and available experimental data.

A DFT study of formation energies of Fe–Zn–Al intermetallics and solutes

Intermetallics, 2012

Sessile ⟨100⟩ self-interstitial clusters with non-parallel edge dumbbells in irradiated bcc Fe and other metals

Scripta Materialia

Density Functional Theory calculations of self-interstitial atom clusters in bcc Fe unexpectedly ... more Density Functional Theory calculations of self-interstitial atom clusters in bcc Fe unexpectedly show that from ~9-14 self-interstitial atoms, an intriguing new family of sessile ⟨100⟩ clusters, surrounded by ⟨110⟩ dumbbells, are more stable than highly mobile clusters of parallel ⟨111⟩ dumbbells. The ⟨110⟩ edge dumbbells find a favorable location in terms of strain energy on the tensile side around the edges of the ⟨100⟩ center, thus stabilizing the clusters. These sessile clusters might explain resistivity recovery results that suggested an absence of glissile self-interstitial clusters up to large cluster sizes in irradiated Fe, while smaller self-interstitial atom clusters likely would have been present. The mechanism of non-parallel edge interstitials stabilizing an otherwise higher energy interstitial loop is also found in some fcc metals.

The effect of Cr concentration on single interstitials stability in FeCr alloys

Oxygen Evolution at Hematite Surfaces: The Impact of Structure and Oxygen Vacancies on Lowering the Overpotential

Journal of Physical Chemistry C, Aug 5, 2016

A molecular dynamics study of ion beam assisted deposition of thin molybdenum films and analysis by thermal desorption spectrometry

Cu/Ta and Ta/Cu thin film growth, studied by Molecular Dynamics simulations

Journal of Computer-aided Materials Design, 2003

The Computational Modeling of Alloys: From Ab Initio and Thermodynamics to Radiation-Induced Heterogeneous Precipitation

Journal: Materials, Apr 1, 2007

Machine learning–enabled high-entropy alloy discovery

Science

High-entropy alloys are solid solutions of multiple principal elements that are capable of reachi... more High-entropy alloys are solid solutions of multiple principal elements that are capable of reaching composition and property regimes inaccessible for dilute materials. Discovering those with valuable properties, however, too often relies on serendipity, because thermodynamic alloy design rules alone often fail in high-dimensional composition spaces. We propose an active learning strategy to accelerate the design of high-entropy Invar alloys in a practically infinite compositional space based on very sparse data. Our approach works as a closed-loop, integrating machine learning with density-functional theory, thermodynamic calculations, and experiments. After processing and characterizing 17 new alloys out of millions of possible compositions, we identified two high-entropy Invar alloys with extremely low thermal expansion coefficients around 2 × 10 −6 per degree kelvin at 300 kelvin. We believe this to be a suitable pathway for the fast and automated discovery of high-entropy alloys...

Machine learning-enabled high-entropy alloy discovery

Science, 2022

High-entropy alloys are solid solutions of multiple principal elements that are capable of reachi... more High-entropy alloys are solid solutions of multiple principal elements that are capable of reaching composition and property regimes inaccessible for dilute materials. Discovering those with valuable properties, however, too often relies on serendipity, because thermodynamic alloy design rules alone often fail in high-dimensional composition spaces. We propose an active learning strategy to accelerate the design of high-entropy Invar alloys in a practically infinite compositional space based on very sparse data. Our approach works as a closed-loop, integrating machine learning with density-functional theory, thermodynamic calculations, and experiments. After processing and characterizing 17 new alloys out of millions of possible compositions, we identified two high-entropy Invar alloys with extremely low thermal expansion coefficients around 2 × 10 −6 per degree kelvin at 300 kelvin. We believe this to be a suitable pathway for the fast and automated discovery of high-entropy alloys with optimal thermal, magnetic, and electrical properties.

Defect and solute properties in dilute Fe-Cr-Ni austenitic alloys from first principles

We present results of an extensive set of first-principles density functional theory calculations... more

High entropy alloys towards industrial applications: High-throughput screening and experimental investigation

Materials Science and Engineering: A, 2022

Using the Thermo-Calc implementation of the CALPHAD approach, high-throughput screening of the Co... more Using the Thermo-Calc implementation of the CALPHAD approach, high-throughput screening of the Co-Cr-Fe-Mn-Ni system was implemented to find &#39;islands&#39; of single phase FCC structure within the compositional space in order to reduce the cost of this well-studied alloy system. The screening identified a region centred around Co 10 Cr 12 Fe 43 Mn 18 Ni 17 , reducing the material cost compared to the equiatomic alloy by ~40%. The alloy was experimentally investigated at room and elevated temperatures, including in-situ tensile testing. The alloy was found to possess slightly lower strength compared to the equiatomic alloy at room temperature, however, exhibited excellent thermal strength up to 873K. Deformation twinning was observed after tensile testing at room temperature, primarily attributed to the reduced stacking fault energy (SFE), which was proven by a thermodynamic model for calculating the SFE. The softening behaviour at room temperature can be explained through solid solution hardening (SSH), whereby a modified approach to Labusch&#39;s model was used to calculate the SSH in reported alloys in this study within the Co-Cr-Fe-Mn-Ni system. The modified models for SFE and SSH are proposed to be implemented into high-throughput screening algorithms for accelerated alloy design towards specific mechanical properties.

Molecular dynamics simulations of ballistic He penetration into W fuzz

Nuclear Fusion, 2016

Brute Force Composition Scanning with a CALPHAD Database to Find Low Temperature Body Centered Cubic High Entropy Alloys

Entropy, 2018

We used the Thermo-Calc High Entropy Alloy CALPHAD database to determine the stable phases of AlC... more We used the Thermo-Calc High Entropy Alloy CALPHAD database to determine the stable phases of AlCrMnNbTiV, AlCrMoNbTiV, AlCrFeTiV and AlCrMnMoTi alloys from 800 to 2800 K. The concentrations of elements were varied from 1–49 atom%. A five- or six-dimensional grid is constructed, with stable phases calculated at each grid point. Thermo-Calc was used as a massive parallel tool and three million compositions were calculated, resulting in tens of thousands of compositions for which the alloys formed a single disordered body centered cubic (bcc) phase at 800 K. By filtering out alloy compositions for which a disordered single phase persists down to 800 K, composition ‘islands’ of high entropy alloys are determined in composition space. The sizes and shapes of such islands provide information about which element combinations have good high entropy alloy forming qualities as well as about the role of individual elements within an alloy. In most cases disordered single phases are formed mos...

MD and BCA simulations of He and H bombardment of fuzz in bcc elements

Journal of Nuclear Materials, 2017

Inconsistencies in modelling interstitials in FeCr with empirical potentials

Computational Materials Science, 2016

Molecular dynamics simulation of graphene on Cu (100) and (111) surfaces

Carbon, 2015

Defect production during ion-assisted deposition of molybdenum films studied by molecular dynamics

MRS Proceedings, 1997

ABSTRACTLow energy argon-ion assisted growth of thin molybdenum films (∼ 60 Å) has been studied b... more ABSTRACTLow energy argon-ion assisted growth of thin molybdenum films (∼ 60 Å) has been studied by molecular dynamics simulations. The effects of a single ion impact are discussed, but more particularly we consider film growth from a manufacturing viewpoint and examine the properties of the completed films. Results for ion-beam assisted deposition are compared with those for unassisted growth (i.e. physical vapor deposition). Surface morphology, defect generation, argon incorporation, and the various responsible atomic mechanisms are discussed.

First-principles study of point defects in an fcc Fe-10Ni-20Cr model alloy

Physical Review B, 2014

On the mobility of vacancy clusters in reduced activation steels: an atomistic study in the Fe–Cr–W model alloy

Journal of Physics: Condensed Matter, 2013

Reduced activation steels are considered as structural materials for future fusion reactors. Besi... more Reduced activation steels are considered as structural materials for future fusion reactors. Besides iron and the main alloying element chromium, these steels contain other minor alloying elements, typically tungsten, vanadium and tantalum. In this work we study the impact of chromium and tungsten, being major alloying elements of ferritic Fe-Cr-W-based steels, on the stability and mobility of vacancy defects, typically formed under irradiation in collision cascades. For this purpose, we perform ab initio calculations, develop a many-body interatomic potential (EAM formalism) for large-scale calculations, validate the potential and apply it using an atomistic kinetic Monte Carlo method to characterize the lifetime and diffusivity of vacancy clusters. To distinguish the role of Cr and W we perform atomistic kinetic Monte Carlo simulations in Fe-Cr, Fe-W and Fe-Cr-W alloys. Within the limitation of transferability of the potentials it is found that both Cr and W enhance the diffusivity of vacancy clusters, while only W strongly reduces their lifetime. The cluster lifetime reduction increases with W concentration and saturates at about 1-2 at.%. The obtained results imply that W acts as an efficient &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;breaker&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; of small migrating vacancy clusters and therefore the short-term annealing process of cascade debris is modified by the presence of W, even in small concentrations.

Interaction of minor alloying elements of high-Cr ferritic steels with lattice defects: An ab initio study

Journal of Nuclear Materials, 2014

Abstract Basic properties of minor alloying elements, namely Mo, W, Nb, Ta, V, Mn, Si entering th... more Abstract Basic properties of minor alloying elements, namely Mo, W, Nb, Ta, V, Mn, Si entering the conventional and reduced-activation structural Fe–(9–12)Cr steels have been analyzed using ab initio calculations. The electronic structure calculations were applied to study the interaction of minor alloying elements with a number of important and well defined lattice structures, such as point defects, the 1/2〈1 1 1〉 screw dislocation core, high angle symmetric grain boundaries and free surfaces. The studied elements were classified according to their similarities and discrepancies regarding the interaction with the above mentioned defects. The refractory alloying elements are found to follow the same trend whereas Mn and Si exhibit peculiar behavior with respect to the interaction with both point and extended lattice defects. The obtained results are discussed and compared with previously published ab initio and available experimental data.

A DFT study of formation energies of Fe–Zn–Al intermetallics and solutes

Intermetallics, 2012