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- Li, Chun-Mei, et al.
(författare)
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Role of magnetic and atomic ordering in the martensitic transformation of Ni-Mn-In from a first-principles study
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:21, s. 214205-
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Tidskriftsartikel (refereegranskat)abstract
- The composition-dependent lattice parameters, crystal structure, elastic properties, magnetic moment, and electronic structure of Ni2Mn1+xIn1-x (0 <= x <= 0.6) are studied by using first-principles calculations. It is shown that the martensitic phase transition (MPT) from cubic L2(1) to tetragonal L1(0) accompanies theMn(Mn)-Mn-In ferromagnetic (FM) to antiferromagnetic (AFM) transition, at around the critical composition x = 0.32, in agreement with the experimental measurement. The Mn-In atomic disorder leads to decreasing stability of the martensite relative to the austenite, which depresses the MPT. The shear elastic constant C' of the parent phase first decreases slightly with increasing x and then remains almost unchanged above x = 0.32, indicating C' alone cannot account for the increase of the MPT temperature with x. The total magnetic moments for the L2(1) phase are in good agreement with those determined by experiments, whereas for the L1(0) phase they are slightly larger than the experimental data due to the possibleMn-In atomic disorder in the sample. The calculated density of states demonstrate that the covalent bonding between the minority spin states of Ni and In plays an important role in both the magnetic and structural stability.
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| 2. |
- Lu, Song, et al.
(författare)
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Determining the minimum grain size in severe plastic deformation process via first-principles calculations
- 2012
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 60:11, s. 4506-4513
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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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| 3. |
- Luo, Hu-Bin, et al.
(författare)
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Phase stability of Ni-2(Mn1-xFex)Ga : A first-principles study
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:2, s. 024427-
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Tidskriftsartikel (refereegranskat)abstract
- Ni-2(Mn1-xFex)Ga ferromagnetic shape memory alloy shows unusual composition-dependent martensitic transformation temperature (T-M), namely, T-M decreases with increasing e/a ratio. In hope of understanding this unusual behavior, we investigated the composition dependence of the heat of formation (H-f) and shear elastic modulus (C') of the cubic austenite as well as the stability of the five-layer modulated (5M) tetragonal martensite relative to the austenite, using first-principles exact muffin-tin orbital method in combination with coherent potential approximation. Our calculations demonstrated that H-f of the austenite increases with the Fe content x. C' increases slightly with x up to 0.05 but decreases thereafter. The composition dependence of both H-f and C' cannot fully account for the trend of T-M against x although such correlations have been proposed in literature for other Ni-Mn-Ga based alloys. The structure of 5M martensite phase of Ni-2(Mn1-xFex)Ga with 0 < x < 0.2 is determined by optimizing both the shear (changing c/a) and wavelike shuffle of atoms in (110) planes along [1 (1) over bar0] direction adopting the experimentally determined modulation function. The energy difference Delta E-AM between the austenite and 5M phases decreases with increasing x up to 0.05, following the lower Delta E-AM corresponding to lower T-M rule. However, with x larger than 0.05, Delta E-AM increases, against the experimental T-M similar to x behavior. We propose that, if taking the temperature effect and the spin-orbital coupling into account, the Delta E-AM similar to x curve might be altered and may explain the unusual composition dependence of Ni-2(Mn1-xFex)Ga.
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