| 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. |
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| 4. |
- Xu, X., et al.
(författare)
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Nanoscale phase separation in a fcc-based CoCrCuFeNiAl0.5 high-entropy alloy
- 2015
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454. ; 84, s. 145-152
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Tidskriftsartikel (refereegranskat)abstract
- Nano-scale phase separation is reported in a nominal single-phase, high-entropy alloy (HEA), which was characterized using scanning transmission electron microscopy (STEM) combined with atom probe tomography (APT). Despite the fact that X-ray diffraction exhibits a single face-centered-cubic (fcc) phase feature of the as-cast alloy prepared by melt spinning, selected area electron diffraction reveals weak L12 ordering in the as-spun alloy. High-resolution STEM shows the presence of two coherent nanophases with distinct L12 and fcc structures, coupling with compositional segregations. The ordering of the L12 domains is enhanced after annealing at 500 °C. Electron energy loss spectroscopy and APT analyses reveal that the L12 nano-phase is enriched with Fe, Co, Cr and Ni, while the fcc domains are a Cu-rich phase. The nano-scale phase separation can effectively minimize the lattice distortions caused by the atomic size difference in the constituent elements, which may offer structural insights into the unusual mechanical behavior and phase stability of fcc HEA.
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