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Sökning: swepub > Johansson Börje > Refereegranskat > Hu Qing Miao

  • Resultat 11-20 av 31
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11.
  • Li, Chun-Mei, et al. (författare)
  • Theoretical investigation of the magnetic and structural transitions of Ni-Co-Mn-Sn metamagnetic shape-memory alloys
  • 2015
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The composition-dependent crystal structure, elastic modulus, phase stability, and magnetic property of Ni2-xCoxMn1.60Sn0.40 (0 <= x <= 0.50) are studied by using first-principles calculations in combination with atomistic spin dynamics method. It is shown that the present lattice parameters and Curie temperature (T-C) are in agreement with the available experimental data. The martensitic phase transformation (MPT) occurs for x < 0.43, where the austenite is in the ferromagnetic (FM) state whereas the martensite is in the antiferromagnetic (AFM) one at 0 K. The x dependence of the lattice parameter, elastic modulus, and energy difference between the FM austenite and the AFM martensite well accounts for the decrease of the MPT temperature (TM) with the Co addition. With increasing x, the increase of the magnetic excitation energy between the paramagnetic and FM austenite of these alloys is in line with the T-C similar to x. The Ni 3d as well as the Co 3d electronic states near the Fermi level are confirmed mainly dominating the phase stability of the studied alloys.
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12.
  • Li, Chun-Mei, et al. (författare)
  • Understanding the martensitic phase transition of Ni-2(Mn1-xFex)Ga magnetic shape-memory alloys from theoretical calculations
  • 2015
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 91:17
  • Tidskriftsartikel (refereegranskat)abstract
    • By using first principles in combination with atomistic spin dynamics calculational methods, we determine the temperature-dependent free energies of the L2(1)-and L1(0)-Ni-2(Mn1-xFex) Ga (0 <= x <= 1), including phonon vibrational and magnetic energies. The x-dependent martensitic phase transformation (MPT) temperature (T-M) and the Curie temperature (T-C) are well represented. It is found that, the abnormal nonmonotonic behavior of T-M similar to x mainly originates from the phonon vibrational free energy. The magnetic energy, which does not change the trend of T-M against x but decreases the driving force of the MPT, is indispensable as well to get reasonable T-M values. This insight provides a good understanding of the physical mechanisms driving the MPT of Ni-2(Mn1-xFex)Ga, and promotes the improvement of their magnetic shape memory properties.
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13.
  • Li, Wei, et al. (författare)
  • Generalized stacking fault energies of alloys
  • 2014
  • Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 26:26, s. 265005-
  • Tidskriftsartikel (refereegranskat)abstract
    • The generalized stacking fault energy (gamma surface) provides fundamental physics for understanding the plastic deformation mechanisms. Using the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation, we calculate the. surface for the disordered Cu-Al, Cu-Zn, Cu-Ga, Cu-Ni, Pd-Ag and Pd-Au alloys. Studying the effect of segregation of the solute to the stacking fault planes shows that only the local chemical composition affects the. surface. The calculated alloying trends are discussed using the electronic band structure of the base and distorted alloys. Based on our. surface results, we demonstrate that the previous revealed 'universal scaling law' between the intrinsic energy barriers (IEBs) is well obeyed in random solid solutions. This greatly simplifies the calculations of the twinning measure parameters or the critical twinning stress. Adopting two twinnability measure parameters derived from the IEBs, we find that in binary Cu alloys, Al, Zn and Ga increase the twinnability, while Ni decreases it. Aluminum and gallium yield similar effects on the twinnability.
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14.
  • Li, Wei, et al. (författare)
  • The effect of Al on the 475 degrees C embrittlement of Fe-Cr alloys
  • 2013
  • Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 74, s. 101-106
  • Tidskriftsartikel (refereegranskat)abstract
    • Aluminum addition to ferritic stainless steels was found to effectively suppress the deleterious 475 degrees C embrittlement resulting from the phase decomposition in concentrated Fe-Cr alloys. With the aim of revealing the mechanism behind this prosperous phenomenon, here we investigate the effect of Al on the interfacial energy and formation energy of Fe-Cr solid solutions. The interface between the decomposed Fe-rich alpha and Cr-rich alpha' phases carries a positive excess energy, which is of significant importance on determining the process of phase separation. Using ab initio alloy theory, we show that for the alpha-Fe70Cr20Al10/alpha'-Fe100-x-yCryAlx (0 <= x <= 10, 55 <= y <= 80) interface, the Al content (x) barely changes the interfacial energy. However, for the alpha-Fe100-x-yCryAlx/alpha'-Fe10Cr90 (0 <= x <= 10, 0 <= y <= 25) interface, the interfacial energy increases with Al content due to the variation of the formation energies of the Fe-Cr alloys upon Al alloying. Our ab initio results are supported by CALPHAD calculations, and suggest that the beneficial effect of Al on ferritic steels is mainly due to its thermodynamical effect on the alpha' phase. 
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15.
  • Lu, Song, et al. (författare)
  • Composition and orientation dependence of the interfacial energy in Fe-Cr stainless steel alloys
  • 2011
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 248:9, s. 2087-2090
  • Tidskriftsartikel (refereegranskat)abstract
    • Using a first-principles quantum mechanical method, we calculated the (001) and (110) interfacial energies between the low temperature alpha and alpha' phases of Fe-Cr alloys as functions of chemical composition. Weshow that the interfacial energies and the interfacial energy anisotropy are highly composition dependent. In particular, the increasing interfacial energy anisotropy with decreasing compositional gap may induce different morphology of the decomposed phases for different compositions of the host alloys.
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16.
  • Lu, Song, et al. (författare)
  • Determining the minimum grain size in severe plastic deformation process via first-principles calculations
  • 2012
  • Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 60:11, s. 4506-4513
  • Tidskriftsartikel (refereegranskat)abstract
    • Although the stacking fault energy (SFE) is a fundamental variable determining the minimum grain size (d(min)) obtainable in severe plastic deformation (SPD) processes, its accurate measurement is difficult. Here we establish the SFEs of binary Pd-Ag, Pd-Cu, Pt-Cu and Ni-Cu solid solutions using the axial interaction model and the supercell model in combination with first-principles theory. The two models yield consistent formation energies. For Pd-Ag, Pd-Cu and Ni-Cu, the theoretical SFEs agree well with those from the experimental measurements. For Pt-Cu no experimental results are available, and thus our calculated SFEs represent the first reasonable predictions. We discuss the correlation of the SFE and d(min), in SPD experiments and show that the d(min) values can be evaluated from first-principles calculations.
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17.
  • Lu, Song, et al. (författare)
  • First-principles study of fcc-Ag/bcc-Fe interfaces
  • 2013
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:22, s. 224104-
  • Tidskriftsartikel (refereegranskat)abstract
    • Ab initio calculations are employed to determine the lower and upper bounds of the interfacial energy and work of separation of a fcc-Ag/bcc-Fe interface. The strain-free interfacial energy of the coherent interface is taken as the lower bound and the interfacial energy of the commensurate incoherent interface as the upper bound of the interfacial energy of a realistic semicoherent interface. The latter is estimated by applying an averaging scheme based on the interfacial energies obtained for the coherent interfaces. Similar calculations are performed for determining the bounds of the work of separation. We justify the use of the averaging scheme by carrying out large supercell calculations for a semicoherent interface. For a Fe(110)/Ag(111) semicoherent interface, we show that taking either Fe or Ag as the underlying lattice, our averaging scheme can yield a reasonable estimation of the work of separation of the semicoherent interface. However, when taking Ag as the underlying lattice, the averaged interfacial energy of the semicoherent interface is significantly underestimated due to the magnetism. The structure and magnetism at the coherent and semicoherent interfaces are discussed.
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18.
  • 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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19.
  • Lu, S., et al. (författare)
  • Rare earth elements in alpha-Ti : A first-principles investigation
  • 2009
  • Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 46:4, s. 1187-1191
  • Tidskriftsartikel (refereegranskat)abstract
    • The interaction energies between substitutional rare earth (RE) atoms, between RE and interstitial C, N, O, H atoms, as well as between RE and vacancies in alpha-Ti are calculated via first-principles density-functional theory with projector augmented-wave (PAW) pseudopotentials. The results show that the RE-vacancy and RE-RE interactions are attractive due to the weaker RE-Ti bond than the host Ti-Ti bond. All of the RE atoms investigated in this paper are repulsive to C and N, but attractive to H. RE-O interactions are repulsive for the light RE atoms, though the interactions are very weak for the heavy RE atoms. The mechanism underlying the interactions and their possible influence on the properties of Ti alloys are discussed.
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20.
  • Lu, Song, et al. (författare)
  • Stacking fault energies of Mn, Co and Nb alloyed austenitic stainless steels
  • 2011
  • Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 59:14, s. 5728-5734
  • Tidskriftsartikel (refereegranskat)abstract
    • The alloying effects of Mn, Co and Nb on the stacking fault energy (SFE) of austenitic stainless steels, Fe-Cr-Ni with various Ni contents, are investigated via quantum-mechanical first-principles calculations. In the composition range (c(Cr) = 20%, 8 <= c(Ni) <= 20%, 0 <= c(Mn), c(Co), c(Nb) <= 8%, balance Fe) studied here, it is found that Mn always decreases the SFE at 0 K but increases it at room temperature in high-Ni (c(Ni) greater than or similar to 16%) alloys. The SFE always decreases with increasing Co content. Niobium increases the SFE significantly in low-Ni alloys; however, this effect is strongly diminished in high-Ni alloys. The SFE-enhancing effect of Ni usually observed in Fe-Cr-Ni alloys is inverted to an SFE-decreasing effect by Nb for c(Nb) greater than or similar to 3%. The revealed nonlinear composition dependencies are explained in terms of the peculiar magnetic contributions to the total SFE.
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  • Resultat 11-20 av 31

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