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Berastegui, Pedro
Publications (10 of 12) Show all publications
Mockute, A., Palisaitis, J., Nedfors, N., Berastegui, P., Broitman, E., Alling, B., . . . Rosen, J. (2019). Synthesis and characterization of (Ti1-xAlx)B2+Delta thin films from combinatorial magnetron sputtering. Thin Solid Films, 669, 181-187
Open this publication in new window or tab >>Synthesis and characterization of (Ti1-xAlx)B2+Delta thin films from combinatorial magnetron sputtering
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2019 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 669, p. 181-187Article in journal (Refereed) Published
Abstract [en]

(Ti1-xAlx)B2+Delta films with a lateral composition gradient of x = [0.30-0.66] and Delta = [0.07-1.22] were deposited on an Al2O3 wafer by dual magnetron sputtering at 400 degrees C from sintered TiB2 and AlB2 targets. Composition analysis indicates that higher Ti:Al ratios favor overstoichiometry in B and a reduced incorporation of O. Transmission electron microscopy reveals distinctly different microstructures of Ti- and Al-rich compositions, with formation of characteristic conical growth features for the latter along with a lower degree of crystallinity and significantly less tissue phase from B segregation at the grain boundaries. For Al-rich films, phase separation into Ti- and Al-rich diboride nanometer-size domains is observed and interpreted as surface-initiated spinodal decomposition. The hardness of the films ranges from 14 to 28 GPa, where the higher values were obtained for the Ti-rich regions of the metal boride.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Titanium aluminium diboride, Thin films, Combinatorial sputtering, Mechanical properties, Phase decomposition
National Category
Materials Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-372875 (URN)10.1016/j.tsf.2018.10.042 (DOI)000453405600026 ()
Funder
Knut and Alice Wallenberg Foundation, KAW 2015.0043Swedish Research Council, 330-2014-6336Swedish Research Council, 2016-04412Swedish Research Council, 642-2013-8020Swedish Foundation for Strategic Research
Available from: 2019-01-10 Created: 2019-01-10 Last updated: 2019-01-10Bibliographically approved
Pacheco, V., Lindwall, G., Karlsson, D., Cedervall, J., Fritze, S., Ek, G., . . . Jansson, U. (2019). Thermal Stability of the HfNbTiVZr High-Entropy Alloy. Inorganic Chemistry, 58(1), 811-820
Open this publication in new window or tab >>Thermal Stability of the HfNbTiVZr High-Entropy Alloy
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2019 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, no 1, p. 811-820Article in journal (Refereed) Published
Abstract [en]

The multicomponent alloy HfNbTiVZr has been described as a single-phase high-entropy alloy (HEA) in the literature, although some authors have reported that additional phases can form during annealing. The thermal stability of this alloy has therefore been investigated with a combination of experimental annealing studies and thermodynamic calculations using the CALPHAD approach. The thermodynamic calculations show that a single-phase HEA is stable above about 830 degrees C. At lower temperatures, the most stable state is a phase mixture of bcc, hcp, and a cubic C15 Laves phase. Annealing experiments followed by quenching confirm the results from thermodynamic calculations with the exception of the Laves phase structure, which was identified as a hexagonal C14 type instead of the cubic C15 type. Limitations of the applied CALPHAD thermodynamic description of the system could be an explanation for this discrepancy. As-synthesized HfNbTiVZr alloys prepared by arc-melting form a single-phase bcc HEA at room temperature. In situ annealing studies of this alloy show that additional phases start to form above 600 degrees C. This indicates that the observed HEA is metastable at room temperature and stabilized by a slow kinetics during cooling. X-ray diffraction analyses using different cooling rates and annealing times show that the phase transformations in this HEA are slow and that completely different phase compositions can be obtained depending on the annealing procedure. In addition, it has been shown that the sample preparation method (mortar grinding, heat treatment, etc.) has a significant influence on the collected diffraction patterns and therefore on the phase identification and analysis.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-375221 (URN)10.1021/acs.inorgchem.8b02957 (DOI)000455289000093 ()30525533 (PubMedID)
Funder
Swedish Foundation for Strategic Research
Available from: 2019-01-30 Created: 2019-01-30 Last updated: 2019-01-30Bibliographically approved
Hedin, A., Johansson, A. J., Lilja, C., Boman, M., Berastegui, P., Berger, R. & Ottosson, M. (2018). Corrosion of copper in pure O2-free water?. Corrosion Science, 137, 1-12
Open this publication in new window or tab >>Corrosion of copper in pure O2-free water?
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2018 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 137, p. 1-12Article in journal (Refereed) Published
Abstract [en]

Copper exposed to pure, O-2-free water for several months in glass- and metal-contained, well-controlled systems shows no evidence of corrosion, either through hydrogen evolution or through the occurrence of oxidized copper. The results contradict the interpretation of recent experiments where it has been claimed that copper corrodes in pure, O-2-free water far above the very limited extent predicted by established thermodynamic data. Reasons for the different experimental outcomes are discussed. Experimental and theoretical efforts to identify hitherto unknown, potentially corrosion driving species of the Cu-O-H system and studies of copper/water surface reactions are reviewed as background for the present study.

Keywords
Copper, Corrosion, Water, Hydrogen
National Category
Corrosion Engineering
Identifiers
urn:nbn:se:uu:diva-387458 (URN)10.1016/j.corsci.2018.02.008 (DOI)000436213400001 ()
Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-06-25Bibliographically approved
Berastegui, P., Tai, C.-W. & Valvo, M. (2018). Electrochemical reactions of AgFeO2 as negative electrode in Li- and Na-ion batteries. Journal of Power Sources, 401, 386-396
Open this publication in new window or tab >>Electrochemical reactions of AgFeO2 as negative electrode in Li- and Na-ion batteries
2018 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 401, p. 386-396Article in journal (Refereed) Published
Abstract [en]

AgFeO2 nanoparticles synthesized via precipitation at room temperature are investigated in Li- and Na-ion cells through electrode coatings with an alginate binder. The electrochemical reactions of AgFeO2 with Li+ and Na+ions, as well as its role as alternative negative electrode in these cell systems are carefully evaluated. Initial Li uptake causes irreversible amorphization of the AgFeO2 structure with concomitant formation of Ag0 nanoparticles. Further Li incorporation results in conversion into Fe0 nanoparticles and Li2O, together with Li-alloying of these Ag0 clusters. Similar mechanisms are also found upon Na uptake, although such processes are hindered by overpotentials, the capacity and reversibility of the reactions with Na+ ions being not comparablewith those of their Li+ counterparts. The behaviour of AgFeO2 at low potentials vs. Li+/Li displays a synergic pseudo-capacitive charge storage overlapping Li-Ag alloying/de-alloying. This feature is exploited in full cells having deeply lithiated AgFeO2 and LiFePO4 as negative and positive electrodes, respectively. These environmentally friendly iron-based full cells exhibit attractive cycle performances with ≈80% capacity retention after 1000 cycles without any electrolyte additive, average round trip efficiency of ≈89% and operational voltage of 3.0 V combined with built-in pseudo-capacitive characteristics that enable high cycling rates up to≈25C.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Silver ferrite, Li- and Na-ion batteries, Negative electrodes, Conversion reactions, Electrochemical alloying, Metallic nanoparticles
National Category
Materials Chemistry Inorganic Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:uu:diva-374936 (URN)10.1016/j.jpowsour.2018.09.002 (DOI)000449444500044 ()
Funder
Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 245-2014-668Knut and Alice Wallenberg FoundationStandUp
Available from: 2019-01-24 Created: 2019-01-24 Last updated: 2019-01-25Bibliographically approved
Braceras, I., Ibanez, I., Taher, M., Mao, F., del Barrio, A., Saenz De Urturi, S., . . . Jansson, U. (2018). On the electro-tribological properties and degradation resistance of silver-aluminum coatings. Wear, 414, 202-211
Open this publication in new window or tab >>On the electro-tribological properties and degradation resistance of silver-aluminum coatings
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2018 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 414, p. 202-211Article in journal (Refereed) Published
Abstract [en]

Contact materials in sliding electrical applications must possess low electrical contact resistance, low friction and wear coefficients, and high degradation resistance to the surrounding media. Silver coatings are commonly used in such applications despite their shortcomings. This work has focused on the study of alternative silver-aluminum coatings deposited by PVD. The main findings include the strong dependence of the tribological performance on the concentration of Al and hence the phases present in the coatings. Besides, the wear mechanism was found to be affected by the working media, either on air or insulating oil. Results have shown that for full HCP phase coatings (Ag67Al33), wear rates are lowest, with no adhesive wear and good surface sulphidation resistance, though with some proclivity to oxidation, coupled with a moderate increase in the electrical contact resistance.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2018
Keywords
Ag-Al coatings, Electro-tribology, PVD, Electrical Contact Resistance, H2S test, Oil immersion
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:uu:diva-369388 (URN)10.1016/j.wear.2018.08.014 (DOI)000448334700021 ()
Available from: 2019-01-15 Created: 2019-01-15 Last updated: 2019-01-15Bibliographically approved
Ottosson, M., Boman, M., Berastegui, P., Andersson, Y., Hahlin, M., Korvela, M. & Berger, R. (2018). Response to the comments by P. Szakalos, T. angstrom kermark and C. Leygraf on the paper "Copper in ultrapure water, a scientific issue under debate" [Letter to the editor]. Corrosion Science, 142, 308-311
Open this publication in new window or tab >>Response to the comments by P. Szakalos, T. angstrom kermark and C. Leygraf on the paper "Copper in ultrapure water, a scientific issue under debate"
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2018 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 142, p. 308-311Article in journal, Letter (Other academic) Published
Keywords
Copper, XPS, AES, Oxidation
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-366387 (URN)10.1016/j.corsci.2018.02.003 (DOI)000444933400030 ()
Available from: 2018-11-21 Created: 2018-11-21 Last updated: 2018-11-21Bibliographically approved
Taher, M., Mao, F., Berastegui, P., Andersson, A. M. & Jansson, U. (2018). The Influence of Chemical and Phase Composition on Mechanical, Tribological and Electrical Properties of Silver-Aluminum alloys. Tribology International, 119, 680-687
Open this publication in new window or tab >>The Influence of Chemical and Phase Composition on Mechanical, Tribological and Electrical Properties of Silver-Aluminum alloys
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2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 119, p. 680-687Article in journal (Refereed) Published
Abstract [en]

Ag1-xAlx alloys were investigated as potential sliding electrical contact materials. Seven Ag1-xAlx alloys, covering the different phase regions on the Ag-Al phase diagram, were prepared by arc melting. X-ray diffraction (XRD), scanning electron microscopy coupled with X-ray spectroscopy (SEM/EDX), X-ray photoelectron spectroscopy (XPS), nano- and microindentation, and four-point electrical contact resistance measurements were employed to characterize the composition, structure, and physicochemical properties of the alloys. The hardness of Ag1-xAlx alloys increases with Al content. The Ag1-xAlx alloys with hexagonal close-packed (hcp) structure exhibit better tribological properties than pure Ag and other phase compositions. The wear mechanisms change from adhesive, for the alloys with low Al content (<= 20 at. %) to oxidative and abrasive wear for the alloys with high Al content (>= 25 at. %). The Ag1-xAlx alloys with hcp structure exhibit the highest wear resistance. Depth-profile XPS data reveal that the oxide layer grows during the triboprocess and that its thickness increases with number of sliding cycles. Ag/Ag1-xAlx contact pairs exhibit higher contact resistance than the Ag/Ag pair and the contact resistance increases with Al content.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-320229 (URN)10.1016/j.triboint.2017.11.026 (DOI)000424960500066 ()
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2017-04-18 Created: 2017-04-18 Last updated: 2018-04-04Bibliographically approved
Taher, M., Mao, F., Berastegui, P., Andersson, A. M. & Jansson, U. (2018). Tuning tribological, mechanical and electrical properties of Ag-X (X=Al, In, Sn) alloys. Tribology International, 125, 121-127
Open this publication in new window or tab >>Tuning tribological, mechanical and electrical properties of Ag-X (X=Al, In, Sn) alloys
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2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 125, p. 121-127Article in journal (Refereed) Published
Abstract [en]

A new design concept for silver based alloys with a hexagonal structure as electrical contact materials with enhanced tribological properties has been investigated. The correlations between the phase composition and the tribological properties have been investigated in the Ag-Al, Ag-In and Ag-Sn systems. In each system, alloys with different chemical compositions were prepared by melting in evacuated ampoules. Characterisation techniques such as: optical microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopies (SEM and TEM) have been used to evaluate the microhardneas, tribological properties and contact resistance of the samples. The phase compositions of the synthesized Ag-Al and Ag-Sn alloys were in agreement with the phase diagrams and the metastable hcp phase was observed in the Ag-In system. The friction coefficients and wear rates of all the hcp-Ag-X (X = Al, In, Sn) alloys were considerably lower than pure Ag or fcc-Ag alloys. This is attributed mainly to easily shearing basal planes in the hcp structure. The Ag-Sn alloys showed high contact resistances, making them less suitable for a sliding electrical contacts. In contrast, the Ag-In alloys showed much lower contact resistance, making them better alternatives for practical applications.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-320227 (URN)10.1016/j.triboint.2018.04.020 (DOI)000435747800014 ()
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage, 38432-1
Available from: 2017-04-18 Created: 2017-04-18 Last updated: 2018-08-27Bibliographically approved
Mockute, A., Palisaitis, J., Alling, B., Berastegui, P., Broitman, E., Naslund, L.-A. -., . . . Rosen, J. (2017). Age hardening in (Ti1-xAlx)B2+Delta thin films. Scripta Materialia, 127, 122-126
Open this publication in new window or tab >>Age hardening in (Ti1-xAlx)B2+Delta thin films
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2017 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 127, p. 122-126Article in journal (Refereed) Published
Abstract [en]

Thin films of (Ti0.71Al0.29)B2+1.08 have been deposited by magnetron sputtering. Post-deposition annealing at 1000 degrees C for 1 h results in increased hardness and elastic modulus, from 32 to 37 GPa and from 436 to 461 GPa, respectively. In both as-deposited and annealed states the films adhere well to the substrate, indicating no considerable internal stress. The initial high hardness is attributed to a columnar microstructure consisting of crystalline (Ti,Al)B-2 columns separated by an amorphous B matrix. The observed age hardening corresponds to phase separation within the (Ti,Al)B-2 columns including the formation of Ti-deficient crystallites within the grain interior upon annealing.

Keywords
Titanium diboride, Thin films, Mechanical properties, Hardness
National Category
Nano Technology Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-308614 (URN)10.1016/j.scriptamat.2016.09.021 (DOI)000386407100028 ()
Funder
EU, FP7, Seventh Framework Programme, 258509Swedish Research Council, 621-2012-4425 642-2013-8020 621-2011-4417 330-2014-6336 622-2008-405 621-2012-4359Swedish Foundation for Strategic Research Knut and Alice Wallenberg Foundation, 2015.0043
Available from: 2016-11-30 Created: 2016-11-29 Last updated: 2018-01-04Bibliographically approved
Kádas, K., Iusan, D., Hellsvik, J., Cedervall, J., Berastegui, P., Sahlberg, M., . . . Eriksson, O. (2017). AlM2B2 (M =Cr, Mn, Fe, Co, Ni): a group of nanolaminated materials. Journal of Physics: Condensed Matter, 29(15), Article ID 155402.
Open this publication in new window or tab >>AlM2B2 (M =Cr, Mn, Fe, Co, Ni): a group of nanolaminated materials
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2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 15, article id 155402Article in journal (Refereed) Published
Abstract [en]

Combining theory with experiments, we study the phase stability, elastic properties, electronic structure and hardness of layered ternary borides AlCr2B2, AlMn2B2, AlFe2B2, AlCo2B2, and AlNi2B2. We find that the first three borides of this series are stable phases, while AlCo2B2 and AlNi2B2 are metastable. We show that the elasticity increases in the boride series, and predict that AlCr2B2, AlMn2B2, and AlFe2B2 are more brittle, while AlCo2B2 and AlNi2B2 are more ductile. We propose that the elasticity of AlFe2B2 can be improved by alloying it with cobalt or nickel, or a combination of them. We present evidence that these ternary borides represent nanolaminated systems. Based on SEM measurements, we demonstrate that they exhibit the delamination phenomena, which leads to a reduced hardness compared to transition metal mono-and diborides. We discuss the background of delamination by analyzing chemical bonding and theoretical work of separation in these borides.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2017
Keywords
nanolaminated ternary borides, phase stability, elastic constants, hardness, scanning electron microscopy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-320624 (URN)10.1088/1361-648X/aa602a (DOI)000397921600002 ()28192279 (PubMedID)
Funder
Swedish Research Council
Available from: 2017-08-15 Created: 2017-08-15 Last updated: 2017-08-15Bibliographically approved
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