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Investigation of compositionally complex refractory metal based thin films
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Oorganisk kemi.ORCID-id: 0000-0001-5445-1374
2024 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Fritextbeskrivning
Abstract [en]

The search for new and improved materials has led to the discovery and establishment of compositionally complex or high-entropy materials. The work in this thesis is focused on the investigation of new compositionally complex materials based on the refractory metals of groups 4-6. The materials in this work were synthesised using non-reactive dc magnetron sputtering and three material systems have been studied: HfNbTiVZr-C, CrTiTaWNb-C and Nb-Mo-C. In the context of compositionally complex materials, this thesis aims to contribute specifically to questions regarding (i) the prediction of phase formation and stability (ii) the chemical interaction between atoms (iii) the correlation between the material properties and compositional complexity. 

The prediction of phase formation and stability using calculated phase diagram (CALPHAD) methods was studied in the HfNbTiVZr-C system. The findings suggest that CALPHAD methods are promising predictive tools, although kinetic effects during synthesis need to be taken into consideration. Furthermore, theoretical, and experimental evidence of charge transfer effects was demonstrated within the HfNbTiVZr-C system. The results of ab initio materials simulations and X-ray Photoelectron Spectroscopy (XPS) measurements highlight the importance of understanding and considering the local chemical environment and chemical interactions in compositionally complex materials.

The approach of metal alloying according to the valence electron concentration (VEC) to tune the mechanical properties was studied in the Nb-Mo-C system. The findings show the importance of microstructural effects on the mechanical properties in the studied thin film materials, which can overshadow the compositional or VEC variations. 

The response to Xe heavy-ion irradiation was studied in the CrTiTaWNb-C system using in situ irradiation experiments. This work presents a comparison between three different compositions: a TaW-rich alloy and carbide thin film as well as a near-equimolar carbide film. The findings indicate that both microstructure and chemical homogeneity play important roles when it comes to radiation damage tolerance in compositional complex materials.

This thesis demonstrates the elaborate and multifaceted nature of compositionally complex materials. Whether it comes to the fundamental understanding or the effective implementation of a materials design tool, many factors need to be taken into consideration, including chemical interactions between the constituent elements and microstructural effects.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2024. , s. 70
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2355
Emneord [en]
Magnetron sputtering, Thin films, High entropy materials, Refractory metals, Transition metal carbides
HSV kategori
Forskningsprogram
Kemi med inriktning mot materialkemi
Identifikatorer
URN: urn:nbn:se:uu:diva-517268ISBN: 978-91-513-2007-6 (tryckt)OAI: oai:DiVA.org:uu-517268DiVA, id: diva2:1826354
Disputas
2024-03-01, Häggsalen - Ångströmlaboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (engelsk)
Opponent
Veileder
Forskningsfinansiär
Swedish Research Council, 2018-04834Tilgjengelig fra: 2024-02-07 Laget: 2024-01-11 Sist oppdatert: 2024-02-07
Delarbeid
1. Investigation of the phase formation in magnetron sputtered hard multicomponent (HfNbTiVZr)C coatings
Åpne denne publikasjonen i ny fane eller vindu >>Investigation of the phase formation in magnetron sputtered hard multicomponent (HfNbTiVZr)C coatings
Vise andre…
2022 (engelsk)Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 221, artikkel-id 111002Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Multicomponent carbides have gained interest especially for ultra-high temperature applications, due to their ceramic hardness, good oxidation resistance and enhanced strength. In this study the phase forma-tion, stability and mechanical properties of (HfNbTiVZr)C multicomponent carbide coatings were inves-tigated. Phase stability was predicted by the CALPHAD (CALculation of PHAse Diagrams) methods. This revealed that the multicomponent solid solution phase is only stable at elevated temperatures, namely above 2400 degrees C. At lower temperatures a phase mixture was predicted, with a particular tendency for V to segregate. Magnetron sputtered thin films deposited at 300 degrees C exhibited a single NaCl-type multicom-ponent carbide phase, which attributes to the kinetic stabilisation of simple structures during thin film growth. Films deposited at 700 degrees C, or exposed to UHV annealing at 1000 degrees C, however, revealed the decom-position of the single-phase multicomponent carbide by partial elemental segregation and formation of additional phases. Thus, confirming the CALPHAD predictions. These results underscore the importance of explicitly considering temperature when discussing the stability of multicomponent carbide materials, as well as the applicability of CALPHAD methods for predicting phase formation and driving forces in these materials. The latter being crucial for designing materials, such as carbides, that are used in appli-cations at elevated temperatures.

sted, utgiver, år, opplag, sider
ElsevierElsevier BV, 2022
Emneord
High entropy ceramics, Multi -principal element carbide, Multicomponent carbide, Physical vapour deposition (PVD), CALPHAD
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-482676 (URN)10.1016/j.matdes.2022.111002 (DOI)000839257000004 ()
Forskningsfinansiär
Swedish Research Council, 2018-04834Swedish Research CouncilSwedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research, RIF14-0053
Tilgjengelig fra: 2022-09-07 Laget: 2022-09-07 Sist oppdatert: 2024-01-15bibliografisk kontrollert
2. Experimental and theoretical evidence of charge transfer in multi-component alloys: how chemical interactions reduce atomic size mismatch
Åpne denne publikasjonen i ny fane eller vindu >>Experimental and theoretical evidence of charge transfer in multi-component alloys: how chemical interactions reduce atomic size mismatch
Vise andre…
2021 (engelsk)Inngår i: Materials Chemistry Frontiers, E-ISSN 2052-1537, Vol. 5, nr 15, s. 5746-5759Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Ab initio simulations of a multi-component alloy using density functional theory (DFT) were combined with experiments on thin films of the same material using X-ray photoelectron spectroscopy (XPS) to study the connection between the electronic and atomic structures of multi-component alloys. The DFT simulations were performed on an equimolar HfNbTiVZr multi-component alloy. Structure and charge transfer were evaluated using relaxed, non-relaxed, as well as elemental reference structures. The use of a fixed sphere size model allowed quantification of charge transfer, and separation into different contributions. The charge transfer was generally found to follow electronegativity trends and results in a reduced size mismatch between the elements, and thus causes a considerable reduction of the lattice distortions compared to a traditional assumption based on tabulated atomic radii. A calculation of the average deviation from the average radius (i.e. the so-called δ-parameter) based on the atomic Voronoi volumes gave a reduction of δ from ca. 6% (using the volumes in elemental reference phases) to ca. 2% (using the volumes in the relaxed multi-component alloy phase). The reliability of the theoretical results was confirmed by XPS measurements of a Hf22Nb19Ti18V19Zr21 thin film deposited by sputter deposition. The experimentally observed core level binding energy shifts (CLS), as well as peak broadening due to a range of chemical surroundings, for each element showed good agreement with the calculated DFT values. The single solid solution phase of the sample was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) including energy dispersive spectroscopy (EDS) with nm-resolution. These observations show that the HfNbTiVZr solid solution phase is non-ideal, and that chemical bonding plays an important part in the structure formation, and presumably also in the properties. Our conclusions should be transferable to other multi-component alloy systems, as well as some other multi-component material systems, and open up interesting possibilities for the design of material properties via the electronic structure and controlled charge transfer between selected metallic elements in the materials.

sted, utgiver, år, opplag, sider
Royal Society of ChemistryRoyal Society of Chemistry (RSC), 2021
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-468314 (URN)10.1039/d1qm00380a (DOI)000664149100001 ()
Forskningsfinansiär
Swedish Research Council, 2018-04834Swedish Research Council, 2019-05403Swedish Research Council, 2018-05973Swedish Research Council, 2019-05487Knut and Alice Wallenberg Foundation, KAW-2018.0194Swedish Foundation for Strategic Research , FFL 15-0290Swedish National Infrastructure for Computing (SNIC)
Tilgjengelig fra: 2022-02-25 Laget: 2022-02-25 Sist oppdatert: 2024-01-15bibliografisk kontrollert
3. Charge transfer effects in (HfNbTiVZr)C – shown by ab-initio calculations and X-ray photoelectron spectroscopy
Åpne denne publikasjonen i ny fane eller vindu >>Charge transfer effects in (HfNbTiVZr)C – shown by ab-initio calculations and X-ray photoelectron spectroscopy
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(engelsk)Inngår i: Artikkel i tidsskrift (Annet vitenskapelig) Submitted
Abstract [en]

Considering charge transfer effects and the variability of the bonding between elements with different electronegativity opens up a deeper understanding of the electronic structure and as a result many of the properties in high entropy related materials. This study investigates the importance of the diverse bonding and chemical environments when discussing multicomponent carbide materials. A combination of ab initio calculations and X-ray photoelectron spectroscopy (XPS) was used to investigate the electronic structure of multicomponent thin films based on the (HfNbTiVZr)C system. The charge transfer was quantified theoretically using relaxed and non-relaxed multicomponent as well as binary carbide reference structures, employing a fixed sphere model. High-resolution XPS spectra from (HfNbTiVZr)C magnetron sputtered thin films displayed core level binding energy shifts and broadening effects as a result of the complex chemical environment. Charge transfer effects and a changed electronic structure in the multicomponent material, compared with the reference binary carbides, are observed both experimentally and in the DFT simulations. The observed effects loosely follow electronegativity considerations, leading to a deviation from an ideal solid solution structure assuming non-distinguishable chemically equivalent environments. 

Emneord
DFT, Magnetron sputtering, Multicomponent carbide, X-ray Photoelectron spectroscopy, Charge transfer
HSV kategori
Forskningsprogram
Kemi med inriktning mot materialkemi
Identifikatorer
urn:nbn:se:uu:diva-517270 (URN)
Tilgjengelig fra: 2024-01-09 Laget: 2024-01-09 Sist oppdatert: 2024-01-19
4. Structural and mechanical properties of magnetron sputtered (NbxMo1-x)C thin films
Åpne denne publikasjonen i ny fane eller vindu >>Structural and mechanical properties of magnetron sputtered (NbxMo1-x)C thin films
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2024 (engelsk)Inngår i: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 224, artikkel-id 113146Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

While transition metal carbides (TMCs) exhibit favourable mechanical properties, alloying according to the valence electron concentration (VEC) has the potential to further enhance the properties of these hard but inherently brittle materials. This study investigates the influence of alloying on the microstructure and mechanical properties of (NbxMo1-x)C carbide films, including binary references and ternary compositions with varying metal ratios (x between 0.35 and 0.53). Furthermore, the influence of various substrate materials is studied by comparing films deposited on Al2O3, MgO and SiO2. All films exhibit a NaCl-type carbide structure and X-ray photoelectron spectroscopy revealed the presence of small amounts of an additional amorphous carbon (a-C) phase. Hardness values around 20 ± 2 GPa were obtained for the films on Al2O3 and MgO, whereas a reduced hardness of 11 ± 1 GPa was observed for the films on SiO2 which is attributed to larger crystallite size and more polycrystalline structure. Overall no clear trend as a function of composition can be noted, indicating that microstructure effects dominate the mechanical properties in this study overshadowing the effect of varying the metal content.

sted, utgiver, år, opplag, sider
Elsevier, 2024
Emneord
Magnetron sputtering, Ceramic coating, Transition metal carbides, Mechanical properties
HSV kategori
Forskningsprogram
Kemi med inriktning mot materialkemi
Identifikatorer
urn:nbn:se:uu:diva-517298 (URN)10.1016/j.vacuum.2024.113146 (DOI)001218592400001 ()
Forskningsfinansiär
Swedish Research Council, 2018-04834Swedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research, RIF14-0053
Tilgjengelig fra: 2024-01-09 Laget: 2024-01-09 Sist oppdatert: 2024-05-31bibliografisk kontrollert
5. From high-entropy alloys to high-entropy ceramics: The radiation-resistant highly concentrated refractory carbide (CrNbTaTiW)C
Åpne denne publikasjonen i ny fane eller vindu >>From high-entropy alloys to high-entropy ceramics: The radiation-resistant highly concentrated refractory carbide (CrNbTaTiW)C
Vise andre…
2023 (engelsk)Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 250, artikkel-id 118856Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

High-entropy materials represent the state-of-the-art on the alloy design strategy for future applications in extreme environments. Recent data indicates that high-entropy alloys (HEAs) exhibit outstanding radiation resistance in face of existing diluted alloy counterparts due to suppressed damage formation and evolution. An extension of the HEA concept is presented in this paper towards the synthesis and characterization of novel high-entropy ceramics as emergent materials for application in environments where energetic particle irradiation is a major concern. A novel carbide within the quinary refractory system CrNbTaTiW has been synthesized using magnetron-sputtering. The material exhibited nanocrystalline grains, single-phase crystal structure and C content around 50 at.%. Heavy-ion irradiation with in-situ Transmission Electron Microscopy was used to assess the irradiation response of the new high-entropy carbide (HEC) at 573 K and a comparison with the HEA within the system is made. No displacement damage effects appear within the microstructures of both HEA and HEC up to a dose of 10 displacements-per-atom. Surprisingly, the HEC has not amorphized under the investigated conditions. Xe was implanted in both materials and bubbles nucleated, but smaller sizes compared with conventional nuclear materials shedding light they are potential candidates for use in nuclear energy.

sted, utgiver, år, opplag, sider
Elsevier, 2023
Emneord
High-entropy ceramics, High-entropy alloys, Nanocrystalline materials, Radiation damage, Extreme environments
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-499313 (URN)10.1016/j.actamat.2023.118856 (DOI)000958714700001 ()
Forskningsfinansiär
EU, European Research Council, 757961Swedish Research Council, 2017-00646_9Swedish Research Council, 2019_00191Swedish Foundation for Strategic Research, RIF14-0053
Tilgjengelig fra: 2023-03-27 Laget: 2023-03-27 Sist oppdatert: 2024-01-11bibliografisk kontrollert
6. Probing the high entropy concept through the irradiation response of near-equimolar (CrTiTaWNb)C ceramic coatings
Åpne denne publikasjonen i ny fane eller vindu >>Probing the high entropy concept through the irradiation response of near-equimolar (CrTiTaWNb)C ceramic coatings
Vise andre…
(engelsk)Manuskript (preprint) (Annet vitenskapelig)
Emneord
High-entropy ceramics, Coatings, radiation damage, extreme environments
HSV kategori
Forskningsprogram
Kemi med inriktning mot materialkemi
Identifikatorer
urn:nbn:se:uu:diva-517271 (URN)
Tilgjengelig fra: 2024-01-07 Laget: 2024-01-07 Sist oppdatert: 2024-01-11

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