| 1. |
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| 2. |
- Jansson, Anna, et al.
(författare)
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Magnetron sputtering of the high entropy alloy CoCrFeMnNi on 316L : Influence of substrate grain orientations
- 2023
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 466
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Tidskriftsartikel (refereegranskat)abstract
- This study explores the influence of a 316L stainless steel substrate on the magnetron sputtering of the Cantor alloy CoCrFeMnNi at different substrate bias. The study was carried out on a polycrystalline 316L substrate where the growth behavior of the coating could be investigated on grains with different orientations. By combining electron backscatter diffraction (EBSD) before and after deposition and characterization of the same area, it was possible to determine growth behaviour and surface morphologies on individual substrate grains. No strong influence of the substrate was observed at a floating bias. At a bias of -100V, however, the coating was strongly influenced by the orientation of the individual substrate grains. Epitaxial coating grains with a smooth surface were observed on the [102]-oriented grains while a more columnar growth was observed on [111]-oriented grains. Furthermore, a small difference in growth rate was observed on different substrate orientations. The growth behaviour could be related to differences in surface energies and diffusion rates on different surface orientations.
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| 3. |
- Kádas, Krisztina, et al.
(författare)
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AlM2B2 (M = Cr, Mn, Fe, Co, Ni) : a group of nanolaminated materials
- 2017
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 29:15
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Berastegui, Pedro, et al.
(författare)
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Magnetron Sputtering of Nanolaminated Cr2AlB2
- 2020
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Ingår i: Coatings. - : MDPI. - 2079-6412. ; 10:8
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Tidskriftsartikel (refereegranskat)abstract
- A ternary Cr(2)AlB(2)phase was deposited as a film using magnetron sputtering. Its anisotropic structure displays both structural and chemical similarities with the nanolaminated MAX phases (M(n+1)AX(n)(n = 1-3) where M usually is an early transition metal, A is typically an element in group 13-14 and X is C or N), and can be described as CrB slabs separated by layers of Al. Combinatorial sputtering was used to optimise the sputtering process parameters for films with the Cr(2)AlB(2)composition. The influences of substrate, temperature and composition were studied using X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopy. Films deposited at room temperature were X-ray amorphous but crystalline films could be deposited on MgO substrates at 680 degrees C using a composite Al-B, Cr and Al targets. X-ray diffraction analyses showed that the phase composition and texture of the films was strongly dependent on the chemical composition. Films with several phases or with a single Cr(2)AlB(2)phase could be deposited, but an additional Al target was required to compensate for a loss of Al at the high deposition temperatures used in this study. The microstructure evolution during film growth was strongly dependent on composition, with a change in texture in Al-rich films from a preferred [010] orientation to a [100]/[001] orientation. A model based on Al desorption from the surface of the growing grains is proposed to explain the texture variations.
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| 5. |
- Braceras, Inigo, et al.
(författare)
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On the electro-tribological properties and degradation resistance of silver-aluminum coatings
- 2018
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Ingår i: Wear. - : ELSEVIER SCIENCE SA. - 0043-1648 .- 1873-2577. ; 414, s. 202-211
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Casillas Trujillo, Luis, et al.
(författare)
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Experimental and theoretical evidence of charge transfer in multi-component alloys : how chemical interactions reduce atomic size mismatch
- 2021
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Ingår i: Materials Chemistry Frontiers. - : Royal Society of Chemistry. - 2052-1537. ; 5:15, s. 5746-5759
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Casillas Trujillo, Luis, et al.
(författare)
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Interstitial carbon in bcc HfNbTiVZr high-entropy alloy from first principles
- 2020
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 4:12
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Tidskriftsartikel (refereegranskat)abstract
- The remarkable mechanical properties of high-entropy alloys can be further improved by interstitial alloying. In this work we employ density functional theory calculations to study the solution energies of dilute carbon interstitial atoms in tetrahedral and octahedral sites in bcc HfNbTiVZr. Our results indicate that carbon interstitials in tetrahedral sites are unstable, and the preferred octahedral sites present a large spread in the energy of solution. The inclusion of carbon interstitials induces large structural relaxations with long-range effects. The effect of local chemical environment on the energy of solution is investigated by performing a local cluster expansion including studies of its correlation with the carbon atomic Voronoi volume. However, the spread in solution energetics cannot be explained with a local environment analysis only pointing towards a complex, long-range influence of interstitial carbon in this alloy.
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| 8. |
- Cedervall, Johan, et al.
(författare)
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Magnetic and mechanical effects of Mn substitutions in AlFe2B2
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 482, s. 54-60
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical and magnetic properties of the newly discovered MAB-phase class of materials based upon AlFe2B2 were investigated. The samples were synthesised from stoichiometric amounts of all constituent elements. X-ray diffraction shows that the main phase is orthorhombic with an elongated b-axis, similar to AlFe2B2. The low hardness and visual inspection of the samples after deformation indicate that these compounds are deformed via a delamination process. When substituting iron in AlFe2B2 with manganese, the magnetism in the system goes from being ferro- to antiferromagnetic via a disordered ferrimagnetic phase exhibited by AlFeMnB2. Density functional theory calculations indicate a weakening of the magnetic interactions among the transitions metal ions as iron is substituted by manganese in AlFe2B2. The Mn-Mn exchange interactions in AlMn2B2 are found to be very small.
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| 9. |
- Chou, Chia-Ying, et al.
(författare)
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Precipitation Kinetics During Post-heat Treatment of an Additively Manufactured Ferritic Stainless Steel
- 2022
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Nature. - 1073-5623 .- 1543-1940. ; 53:8, s. 3073-3082
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure response of laser-powder bed fusion (L-PBF)-processed ferritic stainless steel (AISI 441) during post-heat treatments is studied in detail. Focus is on the precipitation kinetics of the Nb-rich phases: Laves (Fe2Nb) and the cubic carbo-nitride (NbC), as well as the grain structure evolution. The evolution of the precipitates is characterized using scanning and transmission electron microscopy (SEM and TEM) and the experimental results are used to calibrate precipitation kinetics simulations using the precipitation module (TC-PRISMA) within the Thermo-Calc Software package. The calculations reproduce the main trend for both the mean radii for the Laves phase and the NbC, and the amount of Laves phase, as a function of temperature. The calibrated model can be used to optimize the post-heat treatment of additively manufactured ferritic stainless steel components and offer a creator tool for process and structure linkages in an integrated computational materials engineering (ICME) framework for alloy and process development of additively manufactured ferritic steels.
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| 10. |
- Ekberg-Jansson, Ann, 1960, et al.
(författare)
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Bronchial mucosal mast cells in asymptomatic smokers relation to structure, lung function and emphysema
- 2005
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Ingår i: Respir Med. - : Elsevier BV. - 0954-6111 .- 1532-3064. ; 99:1, s. 75-83
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Tidskriftsartikel (refereegranskat)abstract
- The pathologic mechanisms of chronic obstructive pulmonary disease (COPD) most certainly involves neutrophil granulocytes, cytotoxic T-cells, macophages and mast cells. The aim of this study was to investigate the relation between the number of mast cells in different compartments in bronchial biopsies of central proximal airways to structural changes, lung function tests and emphysema detected by high resolution computed tomography (HRCT). Twenty nine asymptomatic smoking and 16 never-smoking men from a population study were recruited. Central bronchial biopsies were stained to identify mast cells by immunohistochemistry. The number of mast cells in the epithelium, lamina propria and smooth muscle as well as epithelial integrity and thickness of the tenascin and laminin layer were determined. Smokers had increased numbers of mast cells in all compartments (P<0.001). Structural changes were correlated to mast cell numbers with the closest associations to mast cell numbers in the smooth muscle [epithelial integrity (R(S)=-0.48, P=0.008), laminin layer (R(S)=0.63, P=0.0002), tenascin layer (R(S)=0.40, P=0.03)]. Similar correlations between mast cells and lung function tests were seen [functional residual capacity (FRC) (R(S)=0.60, P=0.0006), total lung capacity (TLC) (R(S)=0.44, P=0.02) and residual volume (RV) (R(S)=0.41, P=0.03)]. No correlations could be detected between mast cells and FEV1 or to emphysema. Smoking is associated with an increase of mast cells in all compartments of the bronchial mucosa, including smooth muscle, and this is related to altered airway structure and function.
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