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- Li, Xiaojie, et al.
(author)
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Ab initio calculations of mechanical properties of bcc W-Re-Os random alloys : effects of transmutation of W
- 2016
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In: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 28:29
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Journal article (peer-reviewed)abstract
- To examine the effect of neutron transmutation on tungsten as the first wall material of fusion reactors, the elastic properties of W1-x-yRexOsy (0 <= x, y <= 6%) random alloys in body centered cubic (bcc) structure are investigated systematically using the all-electron exact muffin-tin orbitals (EMTO) method in combination with the coherent-potential approximation (CPA). The calculated lattice constant and elastic properties of pure W are consistent with available experiments. Both Os and Re additions reduce the lattice constant and increase the bulk modulus of W, with Os having the stronger effect. The polycrystalline shear modulus, Young's modulus and the Debye temperature increase (decrease) with the addition of Re (Os). Except for C-11, the other elastic parameters including C-12, C-44, Cauchy pressure, Poisson ratio, B/G, increase as a function of Re and Os concentration. The variations of the latter three parameters and the trend in the ratio of cleavage energy to shear modulus for the most dominant slip system indicate that the ductility of the alloy enhances with increasing Re and Os content. The calculated elastic anisotropy of bcc W slightly increases with the concentration of both alloying elements. The estimated melting temperatures of the W-Re-Os alloy suggest that Re or Os addition will reduce the melting temperature of pure W solid. The classical Labusch-Nabarro model for solid-solution hardening predicts larger strengthening effects in W1-yOsy than in W1-xRex. A strong correlation between C' and the fcc-bcc structural energy difference for W1-x-yRexOsy is revealed demonstrating that canonical band structure dictates the alloying effect on C'. The structural energy difference is exploited to estimate the alloying effect on the ideal tensile strength in the [0 0 1] direction.
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| 2. |
- Li, Xiaoqing, et al.
(author)
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Tensile strain-induced softening of iron at high temperature
- 2015
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In: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 5
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Journal article (peer-reviewed)abstract
- In weakly ferromagnetic materials, already small changes in the atomic configuration triggered by temperature or chemistry can alter the magnetic interactions responsible for the non-random atomicspin orientation. Different magnetic states, in turn, can give rise to substantially different macroscopic properties. A classical example is iron, which exhibits a great variety of properties as one gradually removes the magnetic long-range order by raising the temperature towards its Curie point of T-C(degrees) = 1043 K. Using first-principles theory, here we demonstrate that uniaxial tensile strain can also destabilise the magnetic order in iron and eventually lead to a ferromagnetic to paramagnetic transition at temperatures far below T-C(degrees). In consequence, the intrinsic strength of the ideal single-crystal body-centred cubic iron dramatically weakens above a critical temperature of similar to 500 K. The discovered strain-induced magneto-mechanical softening provides a plausible atomic-level mechanism behind the observed drop of the measured strength of Fe whiskers around 300-500 K. Alloying additions which have the capability to partially restore the magnetic order in the strained Fe lattice, push the critical temperature for the strength-softening scenario towards the magnetic transition temperature of the undeformed lattice. This can result in a surprisingly large alloying-driven strengthening effect at high temperature as illustrated here in the case of Fe-Co alloy.
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| 3. |
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| 4. |
- Yang, Yaochun, et al.
(author)
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First-principles study of the Σ3(112) grain boundary in Fe-rich Fe-Cr alloys
- 2020
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In: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 181, s. 140-143
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Journal article (peer-reviewed)abstract
- We report a first-principles investigation of the Sigma 3(112) grain boundary (GB) in body-centered cubic Fe-rich Fe1-xCrx alloy as a function of chemical composition and temperature. The equilibrium amount of Cr at the GB undergoes a sharp transition from slight enrichment in low-alloyed Fe-Cr (x <= 0.06-0.08) to complete Cr saturation for 0.08 <= x <= 0.15. The GB chemistry at room-temperature and below is characterized by miscibility gaps, destabilizing a Fe-Cr interfacial solid solution towards decomposition into Fe-rich and Cr-rich clusters. The Cr-rich clusters at the GB may serve as nucleation centers for secondary phases in Fe-Cr alloys.
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