| 1. |
- Ameyama, Kei, et al.
(författare)
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Harmonic structure, a promising microstructure design
- 2022
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Ingår i: Materials Research Letters. - : Informa UK Limited. - 2166-3831. ; 10:7, s. 440-471
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Tidskriftsartikel (refereegranskat)abstract
- The harmonic structure is a recently introduced concept paving the way for engineering metallic materials to achieve excellent mechanical performance. They consist of soft coarse-grained regions (Core) that are three-dimensionally surrounded by a connected network of hard ultra-fine grained regions (Shell). The interaction in these Core–Shell regions produces a synergistic effect, during plastic deformation, leading to superior mechanical properties that are extremely important in practical applications. The current review paper is aimed at providing a critical assessment on this novel concept of microstructure design. It also involves the identification and critical discussion of key issues which deserve additional studies.
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| 2. |
- Baben, Moritz to, et al.
(författare)
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Unprecedented thermal stability of inherently metastable titanium aluminum nitride by point defect engineering
- 2017
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Ingår i: Materials Research Letters. - : TAYLOR & FRANCIS INC. - 2166-3831. ; 5:3, s. 158-169
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Tidskriftsartikel (refereegranskat)abstract
- Extreme cooling rates during physical vapor deposition (PVD) allow growth of metastable phases. However, we propose that reactive PVD processes can be described by a gas-solid paraequilibrium defining chemical composition and thus point defect concentration. Weshow that this notion allows for point defect engineering by controlling deposition conditions. As example we demonstrate that thermal stability of metastable (Ti, Al) Nx, the industrial benchmark coating for wear protection, can be increased from 800 degrees C to unprecedented 1200 degrees C by minimizing the vacancy concentration. The thermodynamic approach formulated here opens a pathway for thermal stability engineering by point defects in reactively deposited thin films.
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| 3. |
- Bahr, Ahmed, et al.
(författare)
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Quaternary diborides-improving the oxidation resistance of TiB2 +/- z coatings by disilicide alloying
- 2023
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Ingår i: Materials Research Letters. - : Informa UK Limited. - 2166-3831. ; 11:9, s. 733-741
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Tidskriftsartikel (refereegranskat)abstract
- To overcome the limited oxidation resistance of the emerging class of transition metal borides, we suggest within this study novel quaternary diborides, Ti-TM-Si-B-2 +/- z (TM = Ta, Mo), achieving the compromise between excellent oxidation resistance and requirements of hard coatings. Single-phase AlB2-type structured Ti-TM-Si-B-2 +/- z films (3-5 mu m) are sputter-deposited from TiB2/TMSi2 targets. The Ti-Ta-Si-B-2 +/- z coatings exhibit 36 GPa in hardness, while maintaining strongly retarded oxidation kinetics till 1000 degrees C. Ti-Mo-Si-B-2 +/- z coatings preserve a hardness up to 27 GPa, although outperforming all their counterparts by featuring outstanding oxidation resistance with 440nm oxide scale thickness after 1 h at 1200 degrees C. First report on quaternary Ti-TM-Si-B-2 +/- z coatings stabilized in hexagonal AlB2-prototype structures. These hard coating materials exhibit unprecedented oxidation resistance up to 1200 degrees C due to the formation of Si-rich scales.
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| 4. |
- Ding, Haoming, et al.
(författare)
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Synthesis of MAX phases Nb2CuC and Ti2(Al0.1Cu0.9)N by A-site replacement reaction in molten salts
- 2019
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Ingår i: Materials Research Letters. - : Taylor & Francis. - 2166-3831. ; 7:12, s. 510-516
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Tidskriftsartikel (refereegranskat)abstract
- New MAX phases Ti2(AlxCu1−x)N and Nb2CuC were synthesized by A-site replacement by reacting Ti2AlN and Nb2AlC, respectively, with CuCl2 or CuI molten salt. X-ray diffraction, scanning electron microscopy, and atomically resolved scanning transmission electron microscopy showed complete A-site replacement in Nb2AlC, which lead to the formation of Nb2CuC. However, the replacement of Al in Ti2AlN phase was only close to complete at Ti2(Al0.1Cu0.9)N. Density-functional theory calculations corroborated the structural stability of Nb2CuC and Ti2CuN phases. Moreover, the calculated cleavage energy in these Cu-containing MAX phases are weaker than in their Al-containing counterparts.The preparation of MAX phases Nb2CuC and Ti2(Al0.1Cu0.9)N were realized by A-site replacement in Ti2AlN and Nb2AlN, respectively.
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| 5. |
- Guo, Sheng, 1981, et al.
(författare)
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Sunflower-like Solidification Microstructure in a Near-eutectic High-entropy Alloy
- 2013
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Ingår i: Materials Research Letters. - : Informa UK Limited. - 2166-3831. ; 1:4, s. 228-232
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Tidskriftsartikel (refereegranskat)abstract
- Considering the inherent advantages of eutectic alloys as high-temperature materials, eutectic high-entropy alloys provide a brand new research direction for developing materials to be used in high-temperature environments. Along this line of thinking, the solidification microstructure in a near-eutectic Al2CrCuFeNi2 alloy was studied. A unique sunflower-like eutectic colony structure was observed, where the Ni–Al-rich B2 phase formed as the primary phase with a spherical or ellipsoidal morphology, the Ni–Al-rich B2/Cr-rich A2 eutectics grew on the primary phase in a radial manner, and the primary B2 phase further decomposed into nearly cubic particles dispersed in the matrix at lower temperatures.
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| 6. |
- Hanner, Luke A., et al.
(författare)
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Synthesis, characterization and first principle modelling of the MAB phase solid solutions: (Mn1-xCrx)(2)AlB2 and (Mn1-xCrx)(3)AlB4
- 2021
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Ingår i: Materials Research Letters. - : Taylor & Francis. - 2166-3831. ; 9:2, s. 112-118
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Tidskriftsartikel (refereegranskat)abstract
- The MAB phases are a family of layered ternary transition metal borides, with atomically laminated crystal structures comprised of transition metal boride (M-B) layers interleaved by single, or double, Al (A) layers. Herein, density functional theory is implemented to evaluate the thermodynamic stability of disordered (Mn1-xCrx)(2)AlB2, and disordered and ordered (Mn1-xCrx)(3)AlB4 quaternaries. The (Mn1-xCrx)(2)AlB2 solid solutions were synthesized over the entire range of substitution. A (Mn1-xCrx)(3)AlB4 solid solution was produced, on the base of Cr3AlB4, to form (Mn0.33Cr0.66)(3)AlB4. Powder X-ray diffraction shows lattice parameter shifts and unit cell expansions indicative of successful solid solution formations.
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| 7. |
- Hu, Chun, et al.
(författare)
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Influence of co-sputtering AlB2 to TaB2 on stoichiometry of non-reactively sputtered boride thin films
- 2024
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Ingår i: Materials Research Letters. - : TAYLOR & FRANCIS INC. - 2166-3831. ; 12:8, s. 561-570
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal diboride thin films are promising functional materials for their outstanding mechanical properties and thermal stability. By combining experiment and simulations, we discuss angular distribution of the sputtered species, their scattering in the gas phase, re-sputtering and potential evaporation from the grown films for the complex evolution of film compositions, as well as energetic preference for vacancy formation and competing phases as factors for governing the phase constitution. By co-sputtering from two compound targets, we developed phase-pure crystalline (Ta,Al)B2 solid solution thin films and correlate the stoichiometry changes with the evolution of their microstructure, hardness, and elastic modulus. {GRAPHICAL ABSTRACT}
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| 8. |
- Hu, Q., et al.
(författare)
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Anomalous thermal expansion in the deep super-cooled liquid region of a ZrCuAlAg bulk metallic glass
- 2018
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Ingår i: Materials Research Letters. - : Informa UK Limited. - 2166-3831. ; 6:2, s. 121-129
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Tidskriftsartikel (refereegranskat)abstract
- Bulk metallic glasses (BMGs), like other glasses, soften in the super-cooled liquid region (SCLR). Here in this work, surprisingly, a large expansion is reported occurring in the deep SCLR of a Zr 47 Cu 37 Al 8 Ag 8 BMG. Nano-crystals (NCs) are found precipitated during the anomalous expansion of Zr 47 Cu 37 Al 8 Ag 8 , but also in the SCLR of Zr 43 Cu 41 Al 8 Ag 8 that exhibits a conventional softening. It is found that there is a steep composition and density change at the NCs/amorphous matrix transition region in the former alloy, and this transition region exerts a thermal stress of about 0.15 MPa to the surrounding super-cooled liquid (SCL) and drives the soft SCL to expand severely. (Figure presented) IMPACT STATEMENT An anomalous expansion, and particularly a large expansion instead of softening, is reported occurring in the deep SCLR of a Zr-based bulk metallic glass for the first time.
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| 9. |
- Huang, Shuo, et al.
(författare)
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Plastic deformation transition in FeCrCoNiAlx high-entropy alloys
- 2019
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Ingår i: Materials Research Letters. - : Taylor & Francis. - 2166-3831. ; 7:11, s. 439-445
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Tidskriftsartikel (refereegranskat)abstract
- The competition between plastic deformation mechanisms in FeCrCoNiAlx high-entropy alloys is explored as a function of temperature by first-principle theory. Investigating the generalized stacking fault energy, we identify a strong interplay between the magnetic and chemical effects. At cryogenic conditions (ferromagnetic state), full-slip is accompanied by martensitic transformation, whereas increasing temperature towards room-temperature (paramagnetic state) changes the deformation mechanism to full-slip plus twinning. Alloying with Al reduces the susceptibility for stacking fault formation in the ferromagnetic state and promotes twinning in the paramagnetic state. The present advance in magneto-plasticity reveals new opportunities for tailoring the mechanical response in high-entropy alloys. IMPACT STATEMENT: Magnetic state critically affects the γ-surface of FeCrCoNiAlx and is responsible for the emergence of the exceptional metastable twinning phenomena at room temperature.
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| 10. |
- Ingason, Arni Sigurdur, et al.
(författare)
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A Nanolaminated Magnetic Phase: Mn2GaC
- 2014
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Ingår i: Materials Research Letters. - : Taylor & Francis. - 2166-3831. ; 2:2, s. 89-93
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Tidskriftsartikel (refereegranskat)abstract
- Layered magnetic materials are fascinating from the point of view of fundamental science as well as applications. Discoveries such as giant magnetoresistance (GMR) in magnetic multilayers have revolutionized data storage and magnetic recording, and concurrently initiated the search for new layered magnetic materials. One group of inherently nanolaminated compounds are the so called Mn+1AXn (MAX) phases. Due to the large number of isostructural compositions, researchers are exploring the wide range of interesting properties, and not primarily functionalization through optimization of structural quality. Magnetic MAX phases have been discussed in the literature, though this is hitherto an unreported phenomenon. However, such materials would be highly interesting, based on the attractive and useful properties attained with layered magnetic materials to date. Here we present a new MAX phase, (Cr1–xMnx)2GeC, synthesized as thin film in heteroepitaxial form, showing single crystal material with unprecedented structural MAX phase quality. The material was identified using first-principles calculations to study stability of hypothetical MAX phases, in an eort to identify a potentially magnetic material. The theory predicts a variety of magnetic behavior depending on the Mn concentration and Cr/Mn atomic conguration within the sublattice. The analyzed thin films display a magnetic signal well above room temperature and with partly ferromagnetic ordering. These very promising results open up a field of new layered magnetic materials, with high potential for electronics and spintronics applications.
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