Martensitic and Related Transformations in Ni-Al Alloys

Schryvers, D.

doi:10.1051/jp4:1995235

Cited by 8 publications

(6 citation statements)

References 25 publications

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“…The above considerations about δ 0 1 2 1 suggest that the BCC symmetry of the Ni-rich β phase is entropically stabilized at high temperature due to large anharmonic vibrational excitations and becomes dynamically unstable at low temperature. This conjecture is consistent with the martensitic transformations exhibited by Ni-rich β upon quenching 7,8,10,[58][59][60][61][62] . It also suggests that contributions to the free energy from vibrational excitations are especially important in the free energy description of Ni-rich β, more so than for stoichiometric β NiAl and the other compounds of the Ni-Al binary.…”

Section: Discussionsupporting

confidence: 84%

Phase and structural stability in Ni-Al systems from first principles

Goiri

Ven

2016

Phys. Rev. B

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We report on a comprehensive first-principles study of phase stability in the Ni-Al binary, both at zero Kelvin and at finite temperature. First-principles density functional theory calculations of the energies of enumerated orderings on FCC and the sublattices of B2 not only predict the stability of known phases, but also reveal the stability of a family of previously unknown ordered phases that combine features of L12 and L10 in different ratios to adjust their overall composition. The calculations also confirm the stability of vacancy ordered B2 derivatives that are stable in the Al rich half of the phase diagram. We introduce strain order parameters to systematically analyze instabilities with respect to the Bain path connecting the FCC and BCC lattices. Many unstable orderings on both FCC and BCC are predicted around compositions of xNi = 0.625, where a martensitic phase transformation is known to occur. Cluster expansion techniques together with Monte Carlo simulations were used to calculate a finite temperature-composition phase diagram of the Ni-Al binary. The calculated phase diagram together with an analysis of Bain instabilities reveals the importance of anharmonicity in determining the phase bounds between the B2 based β phase and the L12 based γ phase, as well as properties related to martensitic transformations that are observed upon quenching Ni rich β.

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Section: Discussionsupporting

confidence: 84%

Phase and structural stability in Ni-Al systems from first principles

Goiri

Ven

2016

Phys. Rev. B

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“…As a matter of fact, the electron diffraction patterns and TEM micrographs of the microstructure that we observed in our previous works are practically identical to those reported in [9] and those corresponding to the Ni-Al alloy system. In such alloy system, the basic structure (non-modulated) is most often described as a face centered tetragonal with Ll 0 lattice [22]. The differently layered structures are commonly constructed as long period stackings of close-packed planes, derived from the {110}-type planes of austenite, or {111} planes of the Ll 0 cell.…”

Section: Introductionmentioning

confidence: 99%

MARTENSITIC STRUCTURES IN Ni-Mn-Ga

Pons¹,

Santamarta²,

Cesari³

et al. 2001

Applied Crystallography

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The crystal structures of the martensitic phases observed in a variety of Ni-Mn-Ga alloy compositions have been studied and will be reviewed. The martensites already known before, i.e. non-layered (tetragonal), 5-layered and 7-layered, will be discussed in terms of structures modulated by shuffling or as periodic stacking of close packed planes derived from {110} planes of the parent phase (in a similar way as in Ni-Al or Cu-based martensites). Some physical arguments will be given to interpret the 5-layered martensite as a lattice modulated by shuffling and the 7-layered martensite as a periodic stacking of basal planes. Finally, the detailed structure analysis of the "new" 10-layered martensite will be presented. Such structure can be interpreted as a stacking of close-packed planes with the sequence (5 5 ), in Zhdanov notation, resulting in a orthorhombic lattice.

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“…The pioneering efforts in the determination of the modulated crystal structure of Ni-Mn-Ga martensite have used transmission electron microscopy (TEM), where the number of modulation was indicated as nM (5M or 7M for example) according to the number of satellite diffractions plus the main reflection (Pons et al, 2000). Similar to that for the well established Ni-Al alloys (Morito & Otsuka, 1996;Schryvers, 1995), this notation has been habitually adopted to define the number of unit cells of modulated superstructure, as in the Ni-Mn-Ga system the cubic austenite phase shows an analogous displacive martensitic transformation during cooling and the structural modulation is related to the shearing of the parent lattice with the shuffling of atomic layers along certain specific crystallographic directions.…”

Section: Introductionmentioning

confidence: 99%

New approach to twin interfaces of modulated martensite

Zhang

Esling

et al. 2010

J Appl Cryst

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In Ni–Mn–Ga ferromagnetic shape memory alloys, the crystallographic nature of martensitic variant interfaces is one of the key factors governing the variant reorientation through field‐induced interface motion and hence the shape memory performance. So far, the crystal structure studies of these materials – conducted by means of transmission electron microscopy – have suffered from uncertainties in determining the number of unit cells of modulated superstructure, and consequently improper interpretations of orientation correlations of martensitic variants. In this paper a new approach is presented for comprehensive analysis of crystallographic and morphological information of modulated martensite, using automated electron backscatter diffraction. As a first attempt, it has been applied for the unambiguous determination of the orientation relationships of adjacent martensitic variants and their twin interface characters in an incommensurate 7M modulated Ni–Mn–Ga alloy, from which a clear and full‐featured image of the crystallographic nature of constituent twin interfaces is built up. Certainly, this new approach will make it feasible not only to generalize the statistical analysis of martensitic variant distributions for various materials with modulated superstructure, but also to give insight into the crystallographic characteristics of martensitic variant interfaces and the variant reorientation mechanism of new advanced materials for interface engineering.

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Martensitic and Related Transformations in Ni-Al Alloys

Cited by 8 publications

References 25 publications

Phase and structural stability in Ni-Al systems from first principles

Phase and structural stability in Ni-Al systems from first principles

MARTENSITIC STRUCTURES IN Ni-Mn-Ga

New approach to twin interfaces of modulated martensite

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