| 1. |
- Cheng, Q., et al.
(författare)
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Unveiling anneal hardening in dilute Al-doped AlxCoCrFeMnNi (x=0, 0.1) high-entropy alloys
- 2021
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Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 91, s. 270-277
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Tidskriftsartikel (refereegranskat)abstract
- Anneal hardening has been one of the approaches to improve mechanical properties of solid solution alloys with the face-centered cubic (FCC) structure, whereby a considerable strengthening can be attained by annealing of cold-worked alloys below the recrystallization temperature (T-rx). Microscopically, this hardening effect has been ascribed to several mechanisms, i.e. solute segregation to defects (dislocation and stacking fault) and short-range chemical ordering, etc. However, none of these mechanisms can well explain the anneal hardening recently observed in phase-pure and coarse-grained FCC-structured high-entropy alloys (HEAs). Here we report the observations, using high-resolution electron channeling contrast imaging and transmission electron microscopy, of profuse and stable dislocation substructures in a cold-rolled CoCrFeMnNi HEA subject to an annealing below T-rx. The dislocation substructures are observed to be thermally stable up to T-rx, which could arise from the chemical complexity of the high-entropy system where certain elemental diffusion retardation occurs. The microstructure feature is markedly different from that of conventional dilute solid solution alloys, in which dislocation substructures gradually vanish by recovery during annealing, leading to a strength drop. Furthermore, dilute addition of 2 at.% Al leads to a reduction in both microhardness and yield strength of the cold-rolled and subsequently annealed (<= 500 degrees C) HEA. This Al induced softening effect, could be associated with the anisotropic formation of dislocation substructure, resulting from enhanced dislocation planar slip due to glide plane softening effect. These findings suggest that the strength of HEAs can be tailored through the anneal hardening effect from dislocation substructure strengthening.
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| 2. |
- Cheng, Q., et al.
(författare)
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Solid solution softening in a Aloi CoCrFeMnNi high-entropy alloy
- 2020
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 186, s. 63-68
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Tidskriftsartikel (refereegranskat)abstract
- Solute effects on high-entropy alloys of equiatomic proportions are scientifically intriguing because there is no such well-defined "solute" and "solvent" atoms compared to those of conventional single principal element alloys. To date, most of the face-centered cubic alloys exhibit solid solution strengthening rather than softening due to the interactions between dislocations and solute atoms. Here, we present the careful experimental measurements and demonstrate solid solution softening, albeit weak, in a single phase CoCrFeMnNi through the minor addition of 2. at.% Al. This softening effect is mostly related to the decreased Peierl's stress by Al addition.
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| 3. |
- Jiang, Xiangang, et al.
(författare)
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Internal erosion of debris-flow deposits triggered by seepage
- 2023
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Ingår i: Engineering Geology. - : Elsevier BV. - 0013-7952 .- 1872-6917. ; 314, s. 107015-
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Tidskriftsartikel (refereegranskat)abstract
- Debris flows can be triggered by runoffs at considerably steep natural channels and streams. Specifically, runoffgenerated debris-flow deposits are loose mixtures, comprising coarse and fine particles. Owing to seeping water, these fine particles are eroded and transported through the skeleton formed by the coarse particles. Such erosion can modify the porosity of deposits and influence their mechanical characteristics, which can be non-negligible for geotechnical and geological engineering. In this study, seven groups of seepage tests on gravel-sand-clay mixtures with different coarse particle content proportions (48%, 52%, 60%, 70%, 80%, 90%, and 100%) were conducted to investigate the erosion characteristics of debris-flow deposits triggered by seepage flows. In particular, concentrated leak erosion, internal instability erosion, and piping were noted in the soil with a coarse particle content of 48%-80%. Further, when the coarse particle content exceeds 80%, the soil does not disintegrate. A model coupling seepage and internal erosion was also developed to characterise internal erosion. For this model, mass conservation equations were reformulated for different types of internal erosion, based on the assumptions for the pore channel erosion of suspended materials and general erosion. Moreover, an equation based on the internal erosion rate, considering the pore size distribution and hydraulic gradient, was firstly introduced for concentrated leak and internal instability erosion. This equation could efficiently evaluate the mass of particles eroded from the soil. Lastly, the model was calibrated based on experimental data; the corresponding results are discussed herein.
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| 4. |
- Qin, Gang, et al.
(författare)
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A novel face-centered-cubic high-entropy alloy strengthened by nanoscale precipitates
- 2019
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Ingår i: Scripta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6462 .- 1872-8456. ; 172, s. 51-55
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Tidskriftsartikel (refereegranskat)abstract
- A new single-phase face-centered-cubic (FCC) Co9Cr7Cu36Mn25Ni23 [atomic percent, similar hereinafter] high-entropy alloy (HEA) was prepared by arc melting. A uniform distribution of nanometer-sized precipitates was achieved. The tensile yield strength, ultimate tensile strength, and elongation were 401 MPa, 700 MPa, and 36%, respectively. The energy-dispersive spectrometer results showed that the nano-precipitates were rich in Co and Cr elements. Moreover, the crystal-forming behavior and the nanoscale-precipitates-forming mechanism were revealed. Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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| 5. |
- Qin, Gang, et al.
(författare)
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An as-cast high-entropy alloy with remarkable mechanical properties strengthened by nanometer precipitates
- 2020
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Ingår i: Nanoscale. - : ROYAL SOC CHEMISTRY. - 2040-3364 .- 2040-3372. ; 12:6, s. 3965-3976
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Tidskriftsartikel (refereegranskat)abstract
- High-entropy alloys (HEAs) with good ductility and high strength are usually prepared by a combination of forging and heat-treatment processes. In comparison, the as-cast HEAs typically do not reach strengths similar to those of HEAs produced by the forging and heat-treatment processes. Here we report a novel equiatomic-ratio CoCrCuMnNi HEA prepared by vacuum arc melting. We observe that this HEA has excellent mechanical properties, i.e., a yield strength of 458 MPa, and an ultimate tensile strength of 742 MPa with an elongation of 40%. Many nanometer precipitates (5-50 nm in size) and domains (5-10 nm in size) are found in the inter-dendrite and dendrite zones of the produced HEA, which is the key factor for its excellent mechanical properties. The enthalpy of mixing between Cu and Mn, Cr, Co, or Ni is higher than those of mixing between any two of Cr, Co, Ni and Mn, which leads to the separation of Cu from the CoCrCuMnNi HEA. Furthermore, we reveal the nanoscale-precipitate-phase-forming mechanism in the proposed HEA.
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| 6. |
- Qin, Gang, et al.
(författare)
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Experimental and theoretical investigations on the phase stability and mechanical properties of Cr7Mn25Co9Ni23Cu36 high-entropy alloy
- 2021
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 208
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the mechanisms of phase formation and their influence on the mechanical behavior is crucial for materials used in structural applications. Here, the phase decomposition under heat treatment in the Cr7Mn25Co9Ni23Cu36 (atomic percentage) high-entropy alloy and how secondary phases formed affect its tensile mechanical response are reported. The microstructural analysis shows that heat treatment at 800 degrees C /2 h and 600 degrees C /8 h led to the formation of sigma phase, but the sigma phase was not observed for 2 h heat treatment at 600 degrees C and below. The experimentally observed thermal stability and phases are compared to the calculated phase diagram and rationalized by recourse to thermodynamics and kinetics. The mechanism of phase decomposition is discussed based on ab initio calculations, indicating that decomposition into two solid solution phases is energetically preferred over a single solid solution phase with nominal composition.
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| 7. |
- Qu, Muchao, et al.
(författare)
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Mechanical and electrical properties of carbon nanotube/epoxy/glass-fiber composites intended for nondestructive testing
- 2023
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Ingår i: Polymers for Advanced Technologies. - : Wiley. - 1042-7147 .- 1099-1581. ; 34:8, s. 2554-2563
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Tidskriftsartikel (refereegranskat)abstract
- In this study, ternary polymer composites sheets comprising glass fiber (GF) reinforced epoxy with various fractions of carbon nanotubes (CNT) were manufactured using hot-pressing technology. A multiscale morphology analysis was presented using scanning electron microscopy. The thermal behavior of the glass fiber reinforced polymer (GFRP) was investigated using thermogravimetric analysis, DSC, and DMA, which indicated an application temperature up to 71°C for the composites. Mechanical uniaxial stretching and three-points bending tests showed that the addition of 0.1–0.2 wt% CNT decreased the dissipated energy of the specimen by 50% and increased the Young's modulus by more than 100%. During all stretching and bending measurements, the relative change in electrical resistance (RCR) was recorded as function of strain, revealing a relationship between the electrical signal and the applied deformation of the GFRP. Finally, the standard equation for fitting RCR versus strain was optimized, reducing the number of fitting parameters from five to three. The electrical and mechanical properties of the CNT/GF/epoxy composites show that they are suitable sensoring materials for wind-turbine blades and other glass-fiber reinforced epoxy constructions, especially for nondestructive testing.
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| 8. |
- Yu, Qiang, et al.
(författare)
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Unveiling segregation-induced evolution in phase constitution of Cu-containing high-entropy alloys
- 2020
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 843
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical investigation of Cu segregation effect on phase constitution, magnetic, and mechanical properties of FeCoNi(CumAl)(x) high-entropy alloys is presented. Results show that the homogenous FeCoNi(Cu1.0Al)(x) only exists as a single face-centered cubic phase at arbitrary temperatures. The level of Cu-segregation determines the phase evolution amongst inhomogeneous single phase (0.75 <= m < 1.0), duplex phase (m << 0.75), and triple phase (m approximate to 0.75). Our results reproduce the observation. Only face-centered cubic phase can be formed for FeCoNi(CumAl)(x) with either rather low or extreme high content of (CumAl) even though the segregation occurred. The Cu addition lifts the total magnetic moments by enhancing the local magnetic moment of Fe, Co and Ni. The serious Cu segregation in the duplex-phase HEAs induces the decrease of ductility of fcc and bcc phases. The increasing Cu enhances the strength of Cu-rich fcc phase and the decreasing Cu weakens that of Cu-poor bcc phase.
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