Stress-induced transition from modulated 14M to non-modulated martensite in Ni–Mn–Ga alloy

Ge, Yanling; Zárubová, N.; Heczko, Oleg; Hannula, Simo‐Pekka

doi:10.1016/j.actamat.2015.02.028

Cited by 39 publications

(19 citation statements)

References 33 publications

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“…However, the motion of twin boundary is not so simple because the activation energy of the shear induced coherent motion process is not of the same order of magnitude as the magnetocrystalline anisotropy energy which was shown by quasistatic DFT simulations [33,34]. The mechanism includes also twinning dislocations slip along the twinning interfaces, which was confirmed by an experimental transmission electron microscopy measurement [35][36][37]17] and also by DFT calculations in combination with the PeierlsNabarro model [32].…”

Section: Introductionmentioning

confidence: 48%

“…It alternatively interprets the modulated martensites as a periodically nanotwinned tetragonal NM phase with a nanotwin period corresponding to the modulation period [17]. Thus the modulated structures can be described by an alternating sequence of nanotwins with a width of three (101) lattice planes in one orientation and width of two planes in the other for 10M [18] structure or by alternating nanotwins of width five and two (101) lattice planes for 14M structure [19,20].…”

Section: Introductionmentioning

confidence: 99%

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Ab initiostudy of Ni₂MnGa under shear deformation

Zelený

Straka

Sozinov

2015

MATEC Web of Conferences

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Abstract. The effect of shear deformation on Ni2MnGa magnetic shape memory alloy has been investigated using ab initio electronic structure calculations. We used the projector-augmented wave method for the calculations of total energies and stresses as functions of applied affine shear deformation. The studied nonmodulated martensite (NM) phase exhibits a tetragonally distorted L21 structure with c/a > 1. A large strain corresponding to simple shears in <100>{001}, <001>{100} and <010>{100} systems was applied to describe a full path between two equivalent NM lattices. We also studied <10-1>{101} shear which is related to twining of NM phase. Twin reorientation in this system is possible, because applied positive shear results in path with significantly smaller energetic barrier than for negative shear and for shears in other studied systems. When the full relaxation of lattice parameters is allowed, the barriers further strongly decrease and the structures along the twinning path can be considered as orthorhombic.

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Section: Introductionmentioning

confidence: 48%

Section: Introductionmentioning

confidence: 99%

Ab initiostudy of Ni₂MnGa under shear deformation

Zelený

Straka

Sozinov

2015

MATEC Web of Conferences

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“…These may be, for example, refinement in the a/b-lamination, changes in twinning periodicity, changes in stacking of basal planes of 10M structure, or, more generally, as refining or coarsening of adaptive martensite [24,46]. Recently Ge et al [49] demonstrated gradual change of lattice parameters resulting from the coarsening of nanotwins during the 14M→NM transformation observed by TEM. All the mentioned effects can significantly influence the diffraction pattern and can result in an additional or missing diffraction peaks and consequent difficulties in lattice symmetry determination [50,51].…”

Section: Limits Of the Used Lattice Approximationmentioning

confidence: 98%

The relation between lattice parameters and very low twinning stress in Ni₅₀Mn_25+xGa_25−xmagnetic shape memory alloys

Straka

Drahokoupil

Pacherová

et al. 2015

Smart Mater. Struct.

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In search for the origins of the extraordinary low twinning stress of Ni-Mn-Ga magnetic shape memory alloys we studied the thermally induced changes of structure in Ni 50 Mn 25+x Ga 25−x (x=2.7-3.9) single crystal samples and compared them with twinning stress dependences. The alloys exhibited transformation to five-layered (10M) martensite structure between 297 to 328 K. All samples exhibited magnetic shape memory effect. Just below the transformation temperature the samples had very low twinning stress of about 0.1-0.3 MPa, which increased with decreasing temperature. The structural changes were monitored using X-ray diffraction in the temperature range 173-343 K. The 10M structure was approximated by monoclinic lattice with the unit cell derived from the cubic unit cell of the parent L2 1 phase. With decreasing temperature, the lattice parameters a and γ increased, c decreased, while b was nearly constant. For x ≤ 3.5, sudden sharp changes in a and b parameters additionally occurred, resulting in a = b in some regions of the phase diagram, which might be related to the refinement of twin structure of 10M martensite on nanoscale. The temperature dependences of lattice parameter γ (and c or c/a) correlate well with the temperature dependences of twinning stress in agreement with the prediction by a microstructural model of twin boundary motion. On the contrary, there is no correlation between (a − b) and twinning stress. This indicates no significant role of a/b twins or laminate in twin boundary motion mechanism and low twinning stress.

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“…The transformation can be viewed as application of local shear in (101) plane along the [101] direction 35 . The doublelayer nanotwin reorientation was indicated in recent experimental in-situ study of stress-induced 14M → NM transformation using high resolution TEM 36 . Transformation between (32) 2 and (52) 2 structures can be described similarly but mechanism is more complex, because it includes cooperative reorientation of several nanotwin doublelayers.…”

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confidence: 99%

“…Gruner 37 conjectured that the structure based only on oppositely oriented double layers, denoted as 4O 26 , might be even lower in energy by a few meV/f.u than other martensitic structures. Moreover the TEM reveals a very frequent stacking error of modulation in 14M structure, e. g. the sequence of (52225) 36 containing three nanotwin doublelayers, which indicates the stability of doublelayer multistacks. The 4O structure has been suggested for Ni 50 Mn 37 Sb 13 , Ni 50 Mn 37.5 Sn 12.5 and Ni 50 Mn 35 In 15 to explain experimental diffraction patterns 38 but was never reported in Ni-Mn-Ga.…”

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confidence: 99%

Ab initio prediction of stable nanotwin double layers and 4O structure in Ni2MnGa

et al. 2016

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The ab initio electronic structure calculations of the Ni2MnGa alloy indicate that the orthorhombic 4O structure exhibits the lowest energy compared to all known martensitic structures. The 4O structure is formed by nanotwin double layers, i.e., oppositely oriented nanotwins consisting of two (101) lattice planes of nonmodulated martensitic structure. It exhibits the lowest occupation of density of states at the Fermi level. The total energy 1.98 meV/atom below the energy of nonmodulated martensite is achieved within structural relaxation by shifting Mn and Ga atoms at the nanotwin boundaries. The same atomic shift can also be found in other martensitic nanotwinned or modulated structures such as 10M and 14M, which indicates the importance of the nanotwin double layer for the stability of these structures. Our discovery shows that the nanotwinning or modulation is a natural property of low-temperature martensitic phases in Ni-Mn-Ga alloys.PACS numbers: 81.30. Kf, 71.15.Nc, 64.60.My Among Heusler alloys, the Ni 2 MnGa is one of the few, which exhibit the unique properties resulting in a giant magnetic field-induced strain (MFIS) in their lowtemperature martensitic phase 1 . The MFIS can reach up to 12 % in case of Co-and Cu-doped Ni 2 MnGa 2 . Important factors enabling the MFIS are large magnetocrystalline anisotropy and extraordinarily high mobility of martensite twin boundaries 3-6 that primarily depends on martensite structure. While at elevated temperature there is a single austenitic phase of Ni 2 MnGa with cubic L2 1 structure, several low-temperature martensitic phases have been observed depending on composition, temperature and applied stress 7-9 . Martensitic phases with orthorhombic or monoclinic structures exhibit modulation of (110) planes in [110] direction with the periodicity of ten or fourteen lattice planes (10M or 14M). The third martensitic phase with nonmodulated (NM) tetragonally distorted L2 1 structure is typical for larger deviation from stoichiometry. In addition, above the martensitic transformation temperature there is a cubic premartensite with the periodicity of six lattice planes (6M) in alloys with small deviation from stoichiometry 10 .Low-temperature instability of L2 1 austenite can be explained by a strong Fermi surface nesting responsible for the phonon softening in [110] direction, which explains structural modulation of 6M premartensite 11-14 . In addition there is also a large Ni-e g peak corresponding to antibonding states right below the Fermi level, E f , in the minority density of states (DOS) channel. Due to the band Jahn-Teller effect the L2 1 cubic structure lowers its symmetry, which pushes the peak above E f resulting in lower energy [15][16][17] . Nonetheless, the precise causes of the variety of observed low temperature martensitic phases and mechanism of intermartensitic transformations between them have not been fully explained yet.Ab initio calculations have been employed to understand modulations in Ni 2 MnGa. Early works used description of 10M and 14M m...

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Stress-induced transition from modulated 14M to non-modulated martensite in Ni–Mn–Ga alloy

Cited by 39 publications

References 33 publications

Ab initiostudy of Ni₂MnGa under shear deformation

Ab initiostudy of Ni₂MnGa under shear deformation

The relation between lattice parameters and very low twinning stress in Ni₅₀Mn_25+xGa_25−xmagnetic shape memory alloys

Ab initio prediction of stable nanotwin double layers and 4O structure in Ni2MnGa

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Stress-induced transition from modulated 14M to non-modulated martensite in Ni–Mn–Ga alloy

Cited by 39 publications

References 33 publications

Ab initiostudy of Ni2MnGa under shear deformation

Ab initiostudy of Ni2MnGa under shear deformation

The relation between lattice parameters and very low twinning stress in Ni50Mn25+xGa25−xmagnetic shape memory alloys

Ab initio prediction of stable nanotwin double layers and 4O structure in Ni2MnGa

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Ab initiostudy of Ni₂MnGa under shear deformation

Ab initiostudy of Ni₂MnGa under shear deformation

The relation between lattice parameters and very low twinning stress in Ni₅₀Mn_25+xGa_25−xmagnetic shape memory alloys