| 1. |
- 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.
|
|
| 2. |
- 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.
|
|
| 3. |
- Tian, Li-Yun, et al.
(författare)
-
Elastic constants of random solid solutions by SQS and CPA approaches : the case of fcc Ti-Al
- 2015
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 27:31
-
Tidskriftsartikel (refereegranskat)abstract
- Special quasi-random structure (SQS) and coherent potential approximation (CPA) are techniques widely employed in the first-principles calculations of random alloys. Here we scrutinize these approaches by focusing on the local lattice distortion (LLD) and the crystal symmetry effects. We compare the elastic parameters obtained from SQS and CPA calculations, taking the random face-centered cubic (fcc) Ti1-xAlx (0 <= x <= 1) alloy as an example of systems with components showing different electronic structures and bonding characteristics. For the CPA and SQS calculations, we employ the Exact Muffin-Tin Orbitals (EMTO) method and the pseudopotential method as implemented in the Vienna Ab initio Simulation Package (VASP), respectively. We show that the predicted trends of the VASP-SQS and EMTO-CPA parameters against composition are in good agreement with each other. The energy associated with the LLD increases with x up to x = 0.625 similar to 0.750 and drops drastically thereafter. The influence of the LLD on the lattice constants and C12 elastic constant is negligible. C-11 and C-44 decrease after atomic relaxation for alloys with large LLD, however, the trends of C-11 and C-44 are not significantly affected. In general, the uncertainties in the elastic parameters associated with the symmetry lowering turn out to be superior to the differences between the two techniques including the effect of LLD.
|
|
| 4. |
- Wang, Guisheng, 1985-, et al.
(författare)
-
Ab initio prediction of the mechanical properties of alloys : The case of Ni/Mn-doped ferromagnetic Fe
- 2015
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 91:22, s. 224203-
-
Tidskriftsartikel (refereegranskat)abstract
- First-principles alloy theory, formulated within the exact muffin-tin orbitals method in combination with the coherent-potential approximation, is used to study the mechanical properties of ferromagnetic body-centered cubic (bcc) Fe1−xMx alloys (M=Mn or Ni, 0≤x≤0.1). We consider several physical parameters accessible from \emph{ab initio} calculations and their combinations in various phenomenological models to compare the effect of Mn and Ni on the properties of Fe. Alloying is found to slightly alter the lattice parameters and produce noticeable influence on elastic moduli. Both Mn and Ni decrease the surface energy and the unstable stacking fault energy associated with the {110} surface facet and the {110}⟨111⟩ slip system, respectively. Nickel is found to produce larger effect on the planar fault energies than Mn. The semi-empirical ductility criteria by Rice and Pugh consistently predict that Ni enhances the ductility of Fe but give contradictory results in the case of Mn doping. The origin of the discrepancy between the two criteria is discussed and an alternative measure of the ductile-brittle behavior based on the theoretical cleavage strength and single-crystal shear modulus G{110}⟨111⟩ is proposed.
|
|
