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Träfflista för sökning "WFRF:(Johansson Börje) ;pers:(Zhang Hualei)"

Sökning: WFRF:(Johansson Börje) > Zhang Hualei

  • Resultat 1-10 av 17
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2.
  • Laukkanen, P., et al. (författare)
  • Formation and destabilization of Ga interstitials in GaAsN : Experiment and theory
  • 2012
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:19, s. 195205-
  • Tidskriftsartikel (refereegranskat)abstract
    • Using first-principles total energy calculations we have found complex defects induced by N incorporation in GaAsN. The formation energy of the Ga interstitial atom is very significantly decreased due to local effects within the defect complex. The stability of the Ga interstitials is further increased at surfaces. The present results suggest that the energetically favorable Ga interstitial atoms are much more abundant in GaAsN than the previously considered N defects, which have relatively large formation energies. Our synchrotron radiation core-level photoemission measurements support the computational results. The formation of harmful Ga interstitials should be reduced by incorporating large group IV B atoms in GaAsN.
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3.
  • Li, Xiaoqing, et al. (författare)
  • Elastic properties of vanadium-based alloys from first-principles theory
  • 2012
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:1, s. 014105-
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of Cr and Ti on the fundamental mechanical properties of V-Cr-Ti alloys has been investigated using the all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation. The static lattice constant and elastic parameters have been calculated for the body-centered-cubic V1-x-yCrxTiy (0 <= x,y <= 0.1) random solid solution as a function of composition. Our theoretical predictions are in good agreement with the available experimental data. Alloys along the equicomposition region are found to exhibit the largest shear and Young's modulus as a result of the opposite alloying effects obtained for the two cubic shear elastic constants. The classical solid-solution hardening (SSH) model predicts larger strengthening effect in V1-yTiy than in V1-xCrx. By considering a phenomenological expression for the ductile-brittle transition temperature (DBTT) in terms of Peierls stress and SSH, it is shown that the present theoretical results can account for the variations of DBTT with composition.
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4.
  • Li, Xiaoqing, et al. (författare)
  • Tensile strain-induced softening of iron at high temperature
  • 2015
  • Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 5
  • Tidskriftsartikel (refereegranskat)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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5.
  • Lu, Song, et al. (författare)
  • Magnetic effect on the interfacial energy of the Ni(111)/Cr(110) interface
  • 2014
  • Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 26:35, s. 355001-
  • Tidskriftsartikel (refereegranskat)abstract
    • The work of separation and interfacial energy of the Ni(1 1 1)/Cr(1 1 0) interface are calculated via first-principles methods. Both coherent and semicoherent interfaces are considered. We find that magnetism has a significant effect on the interfacial energy, i.e. removing magnetism decreases the interfacial energy of the semicoherent interface by around 50% . Electronic, magnetic and atomic structures at the interface are discussed. An averaging scheme is used to estimate the work of separation and interfacial energy of semicoherent interfaces based on the results of coherent interfaces. The limitations of the scheme are discussed.
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6.
  • Punkkinen, Marko Patrick John, et al. (författare)
  • Adhesion of the iron-chromium oxide interface from first-principles theory
  • 2013
  • Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:49, s. 495501-
  • Tidskriftsartikel (refereegranskat)abstract
    • We determine the interface energy and the work of separation of the Fe/Cr2O3 interface using first-principles density functional theory. Starting from different structures, we put forward a realistic interface model that is suitable to study the complex metal-oxide interaction. This model has the lowest formation energy and corresponds to an interface between Fe and oxygen terminated Cr2O3. The work of separation is calculated to be smaller than the intrinsic adhesion energy of pure Fe or Cr2O3, suggesting that stainless steel surfaces should preferentially break along the metal-oxide interface. The relative stabilities and magnetic interactions of the different interfaces are discussed. Next we introduce Cr atoms into the Fe matrix at different positions relative to the interface. We find that metallic Cr segregates very strongly to the (FeCr)/Cr2O3 interface, and increases the separation energy of the interface, making the adhesion of the oxide scale mechanically more stable. The Cr segregation is explained by the enthalpy of formation.
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8.
  • Zhang, Hualei, et al. (författare)
  • Ab initio calculations of elastic properties of bcc Fe-Mg and Fe-Cr random alloys
  • 2009
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:22
  • Tidskriftsartikel (refereegranskat)abstract
    • Using the ab initio exact muffin-tin orbitals method in combination with the coherent-potential approximation, we have calculated the elastic parameters of ferromagnetic Fe1-mMgm (0 < m < 0.1) and Fe1-cCrc (0 < c < 0.2) random alloys in the body-centered cubic (bcc) crystallographic phase. Results obtained for Fe1-cCrc demonstrate that the employed theoretical approach accurately describes the experimentally observed composition dependence of the polycrystalline elastic moduli of Fe-rich alloys encompassing maximum similar to 10% Cr. The elastic parameters of Fe-Cr alloys are found to exhibit anomalous composition dependence around 5% Cr. The immiscibility between Fe and Mg at ambient conditions is well reproduced by the present theory. The calculated lattice parameter for the Fe-Mg regular solid solution increases by similar to 1.95% when 10% Mg is introduced in Fe, which corresponds approximately to 11% decrease in the average alloy density, in perfect agreement with the experimental finding. At the same time, we find that all of the elastic parameters of bcc Fe-Mg alloys decrease almost linearly with increasing Mg content. The present results show a much stronger alloying effect for Mg on the elastic properties of alpha-Fe than that for Cr. Our results call for further experimental studies on the mechanical properties of the Fe-Mg system.
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9.
  • Zhang, Hualei, et al. (författare)
  • Ab initio determination of the elastic properties of ferromagnetic body-centered cubic Fe-Mn-Al alloys
  • 2015
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 118:10
  • Tidskriftsartikel (refereegranskat)abstract
    • The elastic properties of ferromagnetic Fe1-x-yMnyAlx (0 <= x <= 0.5, y = 0, 0.1, and 0.2) random solid solutions in the body-centered cubic (bcc) crystallographic phase have been investigated using the ab initio exact muffin-tin orbitals method in combination with the coherent-potential approximation. Comparison with the experimental data demonstrates that the employed theoretical approach accurately captures the observed composition dependence of the lattice parameter. The predicted elastic parameters follow complex composition dependence. The C-11, C-12, and C' = (C-11 - C-12)/2 single-crystal elastic constants, the bulk (B), shear (G), and Young's (E) moduli, and the Cauchy pressure (C-12 - C-44) mainly decrease with increasing Al content, whereas the Zener anisotropy ratio (C-44/C') strongly increases with x. C-44 exhibits a non-linear x dependence. The Poisson (v) and Pugh (B/G) ratios first decrease with x but show non-monotonous behavior in high-Al alloys. In terms of the Pugh criterion, these trends suggest an increased brittleness in Al-containing alloys. Manganese has a complex non-monotonous effect on B/G in low-Al alloys (below similar to 15 at. % Al) but enhances the brittleness of the bcc solid solution in large-Al regime. The peculiar Mn alloying effect is explained in terms of magneto-volume mechanisms.
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10.
  • Zhang, Hualei, et al. (författare)
  • Alloying effects on the elastic parameters of ferromagnetic and paramagnetic Fe from first-principles theory
  • 2011
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 110:7, s. 073707-
  • Tidskriftsartikel (refereegranskat)abstract
    • The elastic properties of paramagnetic face-centered-cubic (fcc) Fe(1-x)M(x) (M = Al, Si, V, Cr, Mn, Co, Ni, and Rh; 0 <= x <= 0.1) random alloys are investigated using the exact muffin-tin orbitals density functional method in combination with the coherent-potential approximation. We find that the theoretical lattice parameter of fcc Fe is strongly enlarged by Al, V, and Rh and slightly reduced by Si, Cr, and Co, while it remains nearly constant with Mn and Ni. Both positive and negative alloying effects appear for the elastic constants C(ij)(x) of fcc Fe. These findings are in contrast to those obtained for ferromagnetic body-centered-cubic (bcc) Fe alloys, where all alloying elements considered here are predicted to enlarge the lattice parameter and decrease the C(11)(x) and C(12)(x) elastic constants of bcc Fe. With some exceptions, alloying has much larger effects on ferromagnetic bcc alloys than on paramagnetic fcc ones. Based on the theoretical elastic parameters of the paramagnetic fcc and ferromagnetic bcc phases, simple parameterizations in terms of chemical composition of the equilibrium lattice constants, single-crystal elastic constants, and polycrystalline elastic moduli of Fe-based alloys are presented.
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  • Resultat 1-10 av 17

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