| 51. |
- Hu, Zengyun, et al.
(författare)
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“Dry gets drier, wet gets wetter”: A case study over the arid regions of central Asia
- 2019
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 39:2, s. 1072-1091
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 Royal Meteorological Society The “dry gets drier, wet gets wetter” (DGDWGW) paradigm well describes the pattern of precipitation changes over the oceans. However, it has also been usually considered as a simplified pattern of regional changes in wet/dry under global warming, although GCMs mostly do not agree this pattern over land. To examine the validity of this paradigm over land and evaluate how usage of drought indices estimated from different hydrological variables affects detection of regional wet/dry trends, we take the arid regions of central Asia as a case study area and estimate the drying and wetting trends during the period of 1950–2015 based on multiple drought indices. These indices include the standardized precipitation index (SPI), the standardized precipitation evapotranspiration index (SPEI), the Palmer drought severity index (PDSI) and self-calibrating PDSI (sc_PDSI) with both the Thornthwaite (th) and Penman–Monteith (pm) equations in PDSI calculation (namely, PDSI_th, PDSI_pm, sc_PDSI_th and sc_PDSI_pm). The results show that there is an overall agreement among the indices in terms of inter-annual variation, especially for the PDSIs. All drought indices except SPI show a drying trend over the five states of central Asia (CAS5: including Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan). The four PDSIs and SPEI reveal a wetting tendency over the northwestern China (NW; including Xinjiang Uygur Autonomous Region and Hexi Corridor). The contrasting trends between CAS5 and NW can also be revealed in soil moisture (SM) variations. The nonlinear wet and dry variations are dominated by the 3–7 years oscillations for the indices. Relationships between the six indices and climate variables show the major drought drivers have regional features: with mean temperature (TMP), precipitation total (PRE) and potential evapotranspiration (PET) for CAS5, and PRE and PET for NW. Finally, our analyses indicate that the dry and wet variations are strongly correlated with the El Niño/Southern Oscillation (ENSO).
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| 52. |
- Huang, Shuo, et al.
(författare)
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Chemical ordering controlled thermo-elasticity of AlTiVCr1-xNbx high-entropy alloys
- 2020
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Ingår i: Acta Materialia. - : Pergamon Press. - 1359-6454 .- 1873-2453. ; 199, s. 53-62
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Tidskriftsartikel (refereegranskat)abstract
- The stability of constituent phases in multi-component system always plays a prominent role in tailoring their mechanical performance at elevated temperatures. In this work, we highlight a chemical ordering feature in the AlTiVCr1-xNbx (0 <= x <= 1) alloys with body-centered cubic crystal structure. The quantum-mechanical first-principle investigations of these alloys on the elemental distribution identify a family of B2 type of partially ordered configurations. We map out the elastic parameters in detail as a function of composition and temperature for disordered and partially ordered phases. A great sensitivity to the order-disorder transformation is revealed, especially for the Cr-rich system. Our results demonstrate that a proper control of the ordering level in these alloys can facilitate the optimal tuning of their mechanical performance while keeping the density almost unchanged. The study presented here further predicts that these alloys possess high specific stiffness, low thermal expansion, and large elastic softening resistance. It is demonstrated that the considered alloys have thermal and mechanical properties that compete with superalloys and other high temperature structural materials.
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| 53. |
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| 54. |
- Huang, Shuo, et al.
(författare)
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Mechanical performance of FeCrCoMnAlx high-entropy alloys from first-principle
- 2018
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Ingår i: Materials Chemistry and Physics. - : Elsevier. - 0254-0584 .- 1879-3312. ; 210, s. 37-42
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Tidskriftsartikel (refereegranskat)abstract
- The elastic parameters and ideal tensile strength in the 10011 direction for the body-centered cubic solid solution phase of FeCrCoMnAlx (0.6 <= x <= 1.5) high-entropy alloys are determined using first-principle alloy theory. Based on the estimated theoretical Curie temperatures, all alloys considered here are predicted to order ferromagnetically at room temperature. The mechanical behaviors are analyzed through the single-crystal and polycrystalline elastic moduli, Pugh ratio, and Debye temperature by making use of a series of phenomenological models. High ideal tensile strength is found for the equiatomic FeCrCoMnAl system, and the intrinsic strength increases with decreasing Al content.
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| 55. |
- Huang, Shuo, et al.
(författare)
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Phase-transition assisted mechanical behavior of TiZrHfTax high-entropy alloys
- 2018
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments of high-entropy alloys with high strength and high ductility draw attention to the metastability-engineering strategy. Using first-principle theory, here we demonstrate that reducing the Ta level in the refractory TiZrHfTax system destabilizes the body-centered cubic (bcc) phase and leads to the appearance of the hexagonal close-packed (hcp) phase embedded in the bcc matrix. The alloying-induced features of the elastic parameters for the cubic and hexagonal structures are mapped out in details, and strong sensitivity to the crystal lattice and chemistry is revealed. Results show softening of the bcc matrix with decreasing Ta concentration which ensures ductile behavior. However, the elastically nearly isotropic hcp precipitates possess enhanced resistance against shear which promotes strengthening of the TiZrHfTax dual-phase system. The present atomic-level insight provides strong evidence to the experimental observation, and emphasizes the significance of quantum-design for advanced multi-phase high-entropy alloys with excellent strength-ductility combinations.
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| 56. |
- 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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| 57. |
- Huang, Shuo, et al.
(författare)
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Strengthening Induced by MagnetoChemical Transition in Al-Doped Fe-Cr-Co-Ni High-Entropy Alloys
- 2018
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 10:6
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Tidskriftsartikel (refereegranskat)abstract
- Alloys with adjustable mechanical performance are of fundamental interest in material designs. Here, we investigate the magnetic- and chemical-ordering behavior of the ferromagnetic Fe-Cr-Co-Ni-Al-x (1 <= x <= 2.5) high-entropy alloys with the help of first-principle alloy theory. The lattice constants and the single- and polycrystalline elastic parameters for partially ordered and random structures are considered. In contrast to the trend found for the completely disordered phase, we demonstrate that ordering driven primarily by Al results in an enhanced Young's modulus, especially at high-Al concentrations, which is in line with the observed increase of the hardness for systems with a body-centered-cubic underlying lattice. The results suggest that outstanding strength and ductility can be realized by proper control of the ordering level in single- and multiphase high-entropy alloys.
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| 58. |
- Huang, Shuo, et al.
(författare)
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Temperature dependent stacking fault energy of FeCrCoNiMn high entropy alloy
- 2015
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 108, s. 44-47
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Tidskriftsartikel (refereegranskat)abstract
- The stacking fault energy (SFE) of paramagnetic FeCrCoNiMn high entropy alloy is investigated as a function of temperature via ab initio calculations. We divide the SFE into three major contributions: chemical, magnetic and strain parts. Structural energies, local magnetic moments and elastic moduli are used to estimate the effect of temperature on each term. The present results explain the recently reported twinning observed below room-temperature and predict the occurrence of the hexagonal phase at cryogenic conditions.
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| 59. |
- Huang, Shuo, et al.
(författare)
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Thermal expansion in FeCrCoNiGa high-entropy alloy from theory and experiment
- 2017
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 110:24
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Tidskriftsartikel (refereegranskat)abstract
- First-principle alloy theory and key experimental techniques are applied to determine the thermal expansion of FeCrCoNiGa high-entropy alloy. The magnetic transition, observed at 649 K, is accompanied by a significant increase in the thermal expansion coefficient. The phase stability is analyzed as a function of temperature via the calculated free energies accounting for the structural, magnetic, electronic, vibrational and configurational contributions. The single-and polycrystal elastic modulus for the ferro-and paramagnetic states of the face-centered and body-centered cubic phases are presented. By combining the measured and theoretically predicted temperature-dependent lattice parameters, we reveal the structural and magnetic origin of the observed anomalous thermal expansion behavior. Published by AIP Publishing.
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| 60. |
- Huang, Shuo, et al.
(författare)
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Thermo-elastic behavior of hexagonal Sc-Ti-Zr-Hf high-entropy alloys
- 2022
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 55:23
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in tuning the long-standing strength-ductility tradeoff have drawn attention to high-entropy alloys (HEAs), and the appearance of hexagonal close-packed (hcp) structures has been emphasized. However, few studies have explored the elastic moduli of hcp HEAs, which is of prime importance for improved understanding of the outstanding mechanical properties. In this work, we focus on a set of equiatomic rare-earth-free HEAs with hcp structures, i.e. ScTiZr, ScTiHf, ScZrHf, TiZrHf, and ScTiZrHf, and their thermo-elastic properties are studied using quantum mechanical first-principles methods. It is found that, for all considered HEAs, the hexagonal axial ratio shows a weak dependence on the temperature effect, and the thermal expansion coefficient remains almost unchanged above room temperature. From the calculated temperature-dependent single-crystal elastic constants, we analyzed the mechanical stability, elastic anisotropy, and derived polycrystalline moduli. Results indicate that the present HEAs exhibit rather high elastic isotropy and large elastic softening resistance. The ab initio predicted Young's modulus, shear modulus, and specific modulus do not obey the rule of mixture, which indicates that there exists a strong intrinsic hardening effect in all of the considered HEAs. The calculated results are in good agreement with the available experimental measurements.
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