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Niessen, F., Werner, K. V., Li, W., Lu, S., Vitos, L., Villa, M. & Somers, M. A. J. (2024). Efficient ab initio stacking fault energy mapping for dilute interstitial alloys. Computational materials science, 231, Article ID 112542.
Open this publication in new window or tab >>Efficient ab initio stacking fault energy mapping for dilute interstitial alloys
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2024 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 231, article id 112542Article in journal (Refereed) Published
Abstract [en]

Density Functional Theory (DFT) is the prevalent first principles computational method for determining the stacking fault energy (SFE) of face centered cubic (fcc) metals and alloys. Due to several theoretical and computational challenges, SFE determination for interstitial alloys with alloying elements such as carbon, nitrogen, and hydrogen, has so far been limited to few studies at relatively high interstitial content. We propose a new method, rooted in the axial interaction model, that allows rapid and robust mapping of SFE for virtually arbitrary interstitial contents. Instead of computing the total energy of a very large supercell to represent dilute interstitial solutions, representative interstitial-affected and bulk regions are treated separately at the equivalent volume. The SFE is obtained by balancing the SFE values of the regions with a lever rule approach. The method matches SFE values from the axial interaction model within ≤4 mJ.m−2 error, as validated for non-magnetic fcc Fe-N and paramagnetic fcc Fe-N and AISI 304 alloys. The significantly reduced computational workload and equidistant SFE mapping vs. interstitial content down to extremely low values allows accurate fitting of the SFE vs. interstitial content with only few datapoints. This further improves the computational efficiency. So far DFT-based SFE mapping was limited to purely substitutional alloys; we demonstrate the first-time DFT-based SFE mapping in fcc AISI 304 vs. N and Ni, revealing a non-additive contribution of N and Ni to the SFE. Finally, the remaining challenges and future application for high-throughput DFT SFE computation in interstitial alloys is discussed.

Place, publisher, year, edition, pages
Elsevier, 2024
National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-516352 (URN)10.1016/j.commatsci.2023.112542 (DOI)001088513000001 ()
Funder
VinnovaSwedish Foundation for Strategic ResearchSwedish Research CouncilThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Carl Tryggers foundation
Available from: 2023-11-21 Created: 2023-11-21 Last updated: 2023-11-21Bibliographically approved
Niessen, F., Li, W., Werner, K. V., Lu, S., Vitos, L., Villa, M. & Somers, M. A. J. (2023). Ab initio study of the effect of interstitial alloying on the intrinsic stacking fault energy of paramagnetic gamma-Fe and austenitic stainless steel. Acta Materialia, 253, Article ID 118967.
Open this publication in new window or tab >>Ab initio study of the effect of interstitial alloying on the intrinsic stacking fault energy of paramagnetic gamma-Fe and austenitic stainless steel
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2023 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 253, article id 118967Article in journal (Refereed) Published
Abstract [en]

Intrinsic stacking fault energy (SFE) values of gamma-Fe and AISI 304 austenitic stainless steels were determined as a function of carbon and nitrogen content using ab initio calculations. In contrast to previous investigations, the analysis was conducted incorporating the paramagnetic state to account for the magnetic constitution of real austenitic stainless steels. The effect of finite temperature was partially accounted for by performing ab initio calculations at the experimental volumes at room temperature. Including paramagnetism in gamma-Fe increases the SFE of non-magnetic gamma-Fe by similar to 385 mJ.m(-2). Interstitial alloying of non-magnetic gamma-Fe causes a linear increase in intrinsic stacking fault energy with interstitial content. In comparison, interstitial alloying of paramagnetic gamma-Fe increases the SFE at only about half the rate. The SFE of paramagnetic interstitial-free AISI 304 is within the range of -12 to 0 mJ.m(-2) and only deviates slightly from the SFE of paramagnetic gamma-Fe. It follows a similar, albeit flatter linear dependency on the interstitial content compared to gamma-Fe. Both gamma-Fe and gamma-AISI 304 were found to be metastable in their interstitial-free condition and are stabilized by interstitial alloying. The possible effect of short range ordering between interstitials and Cr on the SFE was discussed. The calculated threshold nitrogen content necessary to stabilize austenite in AISI 304 is in good agreement with experimental investigations of deformation microstructures in dependence of the nitrogen content. Finally, the calculated negative SFE values of AISI 304 were reconciled with experimentally determined positive SFE values using a recent method that accounts for the kinetics of stacking fault formation.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Stacking fault energy, Austenitic stainless steel, Density functional theory modeling, Deformation mode, Martensite formation
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-506580 (URN)10.1016/j.actamat.2023.118967 (DOI)001001405700001 ()
Funder
VinnovaSwedish Foundation for Strategic ResearchSwedish Research CouncilThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Carl Tryggers foundation
Available from: 2023-06-28 Created: 2023-06-28 Last updated: 2023-06-28Bibliographically approved
Huang, S., Dastanpour, E., Schönecker, S., Ström, V., Chai, G., Kiss, L. F., . . . Vitos, L. (2023). Combinatorial design of partial ordered Al-Cr-Mn-Co medium-entropy alloys for room temperature magnetic refrigeration applications. Applied Physics Letters, 123(4), Article ID 044103.
Open this publication in new window or tab >>Combinatorial design of partial ordered Al-Cr-Mn-Co medium-entropy alloys for room temperature magnetic refrigeration applications
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2023 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 123, no 4, article id 044103Article in journal (Refereed) Published
Abstract [en]

Multi-component alloys have received increasing interest for functional applications in recent years. Here, we explore the magnetocaloric response for Al-Cr-Mn-Co medium-entropy alloys by integrated theoretical and experimental methods. Under the guidance of thermodynamic and ab initio calculations, a dual-phase system with large magnetic moment, i.e., Al50Cr19Mn19Co12, is synthesized, and the structural and magnetocaloric properties are confirmed via characterization. The obtained results indicate that the selected alloy exhibits a co-continuous mixture of a disordered body-centered cubic and an ordered B2 phase. The ab initio and Monte Carlo calculations indicate that the presence of the ordered B2 phase is responsible for the substantial magnetocaloric effect. The magnetization measurements demonstrated that this alloy undergoes a second-order magnetic transition with the Curie temperature of similar to 300 K. The magnetocaloric properties are examined using magnetic entropy change, refrigeration capacity, and adiabatic temperature change. The property-directed strategy explored here is intended to contribute to the study of potential multi-component alloys in magnetocaloric applications.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2023
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-510097 (URN)10.1063/5.0160477 (DOI)001036269500006 ()
Funder
Swedish Foundation for Strategic ResearchSwedish Research Council, 2018-05973Vinnova, 2019-05111Swedish Energy AgencyCarl Tryggers foundation , 19:325Carl Tryggers foundation , 20:474
Available from: 2023-08-25 Created: 2023-08-25 Last updated: 2023-08-25Bibliographically approved
Dastanpour, E., Huang, S., Dong, Z., Schönecker, S., Ström, V., Eriksson, O., . . . Vitos, L. (2023). Investigation of the metastable spinodally decomposed magnetic CrFe-rich phase in Al doped CrFeCoNi alloy. Journal of Alloys and Compounds, 939, Article ID 168794.
Open this publication in new window or tab >>Investigation of the metastable spinodally decomposed magnetic CrFe-rich phase in Al doped CrFeCoNi alloy
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2023 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 939, article id 168794Article in journal (Refereed) Published
Abstract [en]

We have conducted an in-depth study of the magnetic phase due to a spinodal decomposition of the BCC phase of a CrFe-rich composition. This magnetic phase is present after casting (arc melting) or water quenching after annealing at 1250 degrees C for 24 h but is entirely absent after annealing in the interval 900-1100 degrees C for 24 h. Its formation is favored in the temperature interval ca 450-550 degrees C and loses magnetization above 640 degrees C. This ferromagnetic-paramagnetic transition is due to a structural transformation from ferromagnetic BCC into paramagnetic sigma and FCC phases. The conclusion from measurements at different heating rates is that both the transformation leading to the increase of the magnetization due to the spinodal decomposition of the parent phase and the vanishing magnetization at 640 degrees C are diffusion controlled.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
High entropy alloy, AlCrFeCoNi, Spinodal decomposition, Structural transformation, Magnetization
National Category
Metallurgy and Metallic Materials Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-506587 (URN)10.1016/j.jallcom.2023.168794 (DOI)000996492500001 ()
Funder
Swedish Foundation for Strategic ResearchSwedish Research Council, 2017- 06474Swedish Research Council, 2019-04971Vinnova, 2019-05111Carl Tryggers foundation , 19:325Carl Tryggers foundation , 20:474
Available from: 2023-06-28 Created: 2023-06-28 Last updated: 2023-06-28Bibliographically approved
El-Tahawy, M., Peter, L., Gubicza, J., Molnar, G., Li, C., Vitos, L. & Bakonyi, I. (2023). Metastable Phase Formation in Electrodeposited Co-Rich Co-Cu and Co-Ni Alloys. Journal of the Electrochemical Society, 170(6), Article ID 062507.
Open this publication in new window or tab >>Metastable Phase Formation in Electrodeposited Co-Rich Co-Cu and Co-Ni Alloys
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2023 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 170, no 6, article id 062507Article in journal (Refereed) Published
Abstract [en]

In a previous work [El-Tahawy et al., J. Magn. Magn. Mater. 560, 169660 (2022)], we reported that from a sulfate type bath, hcp-Co can be electrodeposited at high pH and low current density and investigated the structure and magnetoresistance (MR) characteristics of such hcp-Co electrodeposits. Based on this earlier work, Co-rich Co-Cu and Co-Ni alloy electrodeposits were prepared under the same conditions by adding varying amounts of CuSO4 and NiSO4, respectively, to the CoSO4 bath. According to the results of detailed structural studies by various X-ray diffraction (XRD) geometries, in both the Co-Cu and Co-Ni systems an hcp phase formed exclusively up to about 2 at% of the alloying element. Above this concentration, a significant fcc phase fraction appeared in Co-Cu and a minor fcc fraction in Co-Ni up to about 8 at%. This means that the destabilization effect of Cu on hcp-Co is higher than that of Ni. Although the reduction of the stability of hcp-Co with increasing Cu and Ni content is a well-known phenomenon, a quantitative comparison of this effect in Co-Cu and Co-Ni alloys is missing from the literature. The measured lattice constants are analyzed in comparison with Vegard's law for the Co-Cu and Co-Ni element pairs deduced from data previously reported for the hcp and fcc phases of all three pure elements. For Co-rich Co-Ni alloys, the concentration dependence of the lattice parameters was found to follow Vegard's law for both the hcp and fcc phases due to the miscibility of the two components. For the Co-rich Co-Cu alloys, the data indicate a positive deviation from Vegard's law for both the hcp and fcc phases in agreement with the known similar behavior of fcc Co-Cu alloys for the whole composition range. The positive deviation from Vegard's law in the Co-Cu system is due to the excess mixing volume required for solid solution alloy formation of these immiscible elements in either phases. The MR data are discussed in the light of the observed phases and of the MR parameters reported in our previous work on the hcp and fcc phases of pure Co.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2023
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-508177 (URN)10.1149/1945-7111/acde64 (DOI)001018366900001 ()
Available from: 2023-07-21 Created: 2023-07-21 Last updated: 2023-07-21Bibliographically approved
Dastanpour, E., Huang, S., Schönecker, S., Mao, H., Ström, V., Eriksson, O., . . . Vitos, L. (2023). On the structural and magnetic properties of Al-rich high entropy alloys: a joint experimental-theoretical study. Journal of Physics D: Applied Physics, 56(1), Article ID 015003.
Open this publication in new window or tab >>On the structural and magnetic properties of Al-rich high entropy alloys: a joint experimental-theoretical study
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2023 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 56, no 1, article id 015003Article in journal (Refereed) Published
Abstract [en]

The present work investigates how the vanadium (V) content in a series of Al50Vx(Cr0.33Mn0.33Co0.33)(50−x) (x = 12.5, 6.5, 3.5, and 0.5 at.%) high-entropy alloys affects the local magnetic moment and magnetic transition temperature as a step towards developing high-entropy functional materials for magnetic refrigeration. This has been achieved by carrying out experimental investigations on induction melted alloys and comparison to ab initio and thermodynamic calculations. Structural characterization by x-ray diffraction and scanning electron microscopy indicates a dual-phase microstructure containing a disordered body-centered cubic (BCC) phase and a B2 phase with long-range order, which significantly differ in the Co and V contents. Ab initio calculations demonstrate a weaker magnetization and lower magnetic transition temperature (TC) of the BCC phase in comparison with the B2 phase. We find that lower V content increases the B2 phase fraction, the saturation magnetization, and the Curie point, in line with the calculations. This trend is primarily connected with the preferential partition of V in the BCC phase, which however hinders the theoretically predicted antiferromagnetic B2 phase stabilizing effect of V. On the other hand, the chemistry-dependent properties of the ferromagnetic B2 phase suggest that a careful tuning of the composition and phase fractions can open the way towards promising high-entropy magnetic materials.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2023
Keywords
magnetic materials, high entropy alloys, ab initio, B2 structure, magnetic transition temperature, V content
National Category
Condensed Matter Physics Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-493333 (URN)10.1088/1361-6463/aca1ce (DOI)000897771000001 ()
Funder
Swedish Foundation for Strategic ResearchSwedish Research Council, 2017-06474Swedish Research Council, 2019-04971Vinnova, 2019-05111Carl Tryggers foundation , 19:325Carl Tryggers foundation , 20:474
Available from: 2023-01-17 Created: 2023-01-17 Last updated: 2023-01-17Bibliographically approved
Werner, K. V., Niessen, F., Luo, W., Lu, S., Vitos, L., Villa, M. & Somers, M. A. J. (2023). Reconciling experimental and theoretical stacking fault energies in face-centered cubic materials with the experimental twinning stress. Materialia, 27, Article ID 101708.
Open this publication in new window or tab >>Reconciling experimental and theoretical stacking fault energies in face-centered cubic materials with the experimental twinning stress
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2023 (English)In: Materialia, E-ISSN 2589-1529, Vol. 27, article id 101708Article in journal (Refereed) Published
Abstract [en]

Stacking fault energy and twinning stress are thought to be closely correlated. All currently available models predict a monotonous decrease in twinning stress with decreasing stacking fault energy and depart from the assumption that the intrinsic stacking fault energy has a positive value. Opposite to this prediction, for mediumand high-entropy alloys the twinning stress was shown to increase with decreasing SFE. Additionally, for metastable materials, first principles methods predict negative intrinsic stacking fault energy values, whilst experimentally determined values are always positive. In the present communication, it is postulated that the twinning stress scaled by the Burgers vector bridges the difference between intrinsic and experimentally measured stacking fault energy. The assumption is tested for Cu-Al alloys, for pure metals and for medium- and high-entropy alloys and, for the first time, provides a consistent quantitative interpretation of data for both alloys with positive and negative stacking fault energy.

Place, publisher, year, edition, pages
ElsevierELSEVIER SCI LTD, 2023
Keywords
Metastable phases, Stacking fault energy, Twinning, Density functional theory
National Category
Metallurgy and Metallic Materials Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-501157 (URN)10.1016/j.mtla.2023.101708 (DOI)000964565400001 ()
Available from: 2023-05-05 Created: 2023-05-05 Last updated: 2024-01-15Bibliographically approved
Li, C., Lu, S., Divinski, S. & Vitos, L. (2023). Theoretical and experimental grain boundary energies in body-centered cubic metals. Acta Materialia, 255, Article ID 119074.
Open this publication in new window or tab >>Theoretical and experimental grain boundary energies in body-centered cubic metals
2023 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 255, article id 119074Article in journal (Refereed) Published
Abstract [en]

Grain boundary energy (GBE) and its temperature dependence in body-centered cubic (bcc) metals are investigated using ab initio calculations. We reveal a scaling relationship between the GBEs of the same grain boundary structure in different bcc metals and find that the scaling factor can be best estimated by the ratio of the low-index surface energy. Applying the scaling relationship, the general GBEs of bcc metals at 0 K are predicted. Furthermore, adopting the Foiles's method which assumes that the general GBE has the same temperature dependence as the elastic modulus co[Scr. Mater., 62 (2010) 231-234], the predicted general GBEs at elevated temperatures are found in good agreement with available experimental data. Reviewing two experimental methods for determining the general GBEs, we conclude that the two sets of experimental GBEs for bcc metals correspond to different GB structural spaces and differ by approximately a factor of 2. The present work puts forward an efficient methodology for predicting the general GBEs of metals, which has the potential to extend its application for homogeneous alloys without strong segregation of the alloying element and facilitates GB engineering for advanced alloy design.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2023
Keywords
Grain boundary energy, Temperature dependence, Surface energy, Ab initio, Bcc metals
National Category
Condensed Matter Physics Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-508411 (URN)10.1016/j.actamat.2023.119074 (DOI)001025817300001 ()
Funder
VinnovaSwedish Research Council, 2022-06725Swedish Foundation for Strategic ResearchVinnovaThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Carl Tryggers foundation
Available from: 2023-08-03 Created: 2023-08-03 Last updated: 2023-08-03Bibliographically approved
Lu, S., Sun, X., Tian, Y., An, X., Li, W., Chen, Y., . . . Vitos, L. (2023). Theory of transformation-mediated twinning. PNAS NEXUS, 2(1), Article ID pgac282.
Open this publication in new window or tab >>Theory of transformation-mediated twinning
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2023 (English)In: PNAS NEXUS, ISSN 2752-6542, Vol. 2, no 1, article id pgac282Article in journal (Refereed) Published
Abstract [en]

High-density and nanosized deformation twins in face-centered cubic (fcc) materials can effectively improve the combination of strength and ductility. However, the microscopic dislocation mechanisms enabling a high twinnability remain elusive. Twinning usually occurs via continuous nucleation and gliding of twinning partial dislocations on consecutive close-packed atomic planes. Here we unveil a completely different twinning mechanism being active in metastable fcc materials. The transformation-mediated twinning (TMT) is featured by a preceding displacive transformation from the fcc phase to the hexagonal close-packed (hcp) one, followed by a second-step transformation from the hcp phase to the fcc twin. The nucleation of the intermediate hcp phase is driven by the thermodynamic instability and the negative stacking fault energy of the metastable fcc phase. The intermediate hcp structure is characterized by the easy slips of Shockley partial dislocations on the basal planes, which leads to both fcc and fcc twin platelets during deformation, creating more twin boundaries and further enhancing the prosperity of twins. The disclosed fundamental understanding of the complex dislocation mechanism of deformation twinning in metastable alloys paves the road to design novel materials with outstanding mechanical properties.

Place, publisher, year, edition, pages
Oxford University Press, 2023
Keywords
twinning, martensitic transformation, stacking fault, metastable alloy
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-515040 (URN)10.1093/pnasnexus/pgac282 (DOI)001063362300006 ()36712941 (PubMedID)
Funder
Swedish Research CouncilSwedish Foundation for Strategic ResearchAustralian Research Council, DE170100053Australian Research Council, DE210101773Carl Tryggers foundation The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2023-11-03 Created: 2023-11-03 Last updated: 2023-11-03Bibliographically approved
Choi, Y., Dong, Z., Li, W., Lizarraga, R., Kwon, S.-K. & Vitos, L. (2022). Density Functional Theory Description of Paramagnetic Hexagonal Close-Packed Iron. Materials, 15(4), Article ID 1276.
Open this publication in new window or tab >>Density Functional Theory Description of Paramagnetic Hexagonal Close-Packed Iron
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2022 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 15, no 4, article id 1276Article in journal (Refereed) Published
Abstract [en]

The hexagonal close-packed (hcp) phase of iron is unstable under ambient conditions. The limited amount of existing experimental data for this system has been obtained by extrapolating the parameters of hcp Fe-Mn alloys to pure Fe. On the theory side, most density functional theory (DFT) studies on hcp Fe have considered non-magnetic or ferromagnetic states, both having limited relevance in view of the current understanding of the system. Here, we investigate the equilibrium properties of paramagnetic hcp Fe using DFT modelling in combination with alloy theory. We show that the theoretical equilibrium c/a and the equation of state of hcp Fe become consistent with the experimental values when the magnetic disorder is properly accounted for. Longitudinal spin fluctuation effects further improve the theoretical description. The present study provides useful data on hcp Fe at ambient and hydrostatic pressure conditions, contributing largely to the development of accurate thermodynamic modelling of Fe-based alloys.

Place, publisher, year, edition, pages
MDPI AG, 2022
Keywords
hexagonal close-packed phase of iron, magnetic disorder
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-470351 (URN)10.3390/ma15041276 (DOI)000765292500001 ()35207819 (PubMedID)
Funder
Swedish Research Council, 2015-5335Swedish Research Council, 2017-06474Swedish Research Council, 2019-04971Swedish Foundation for Strategic Research , S14-0038Swedish Foundation for Strategic Research , SM16-0036
Available from: 2022-03-23 Created: 2022-03-23 Last updated: 2022-03-23Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2832-3293

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