Phase Equilibria and Phase Transformations in New B2-type Ferromagnetic Shape Memory Alloys of Co-Ni-Ga and Co-Ni-Al Systems

Oikawa, Katsunari; Ota, Takuya; Gejima, Fumihiko; Ohmori, Toshihiro; Kainuma, Ryosuke; Ishida, K.

doi:10.2320/matertrans.42.2472

Cited by 270 publications

(195 citation statements)

References 12 publications

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“…al. [4]. In our study we concluded that the primary formation of FCC phase can be avoided by increasing the Ga content; however, the martensitic transformation is either suppressed to temperatures far below room temperature or eliminated completely due to the lowering of the electron concentration.…”

Section: Introductionmentioning

confidence: 83%

“…Initial measurements on Co-Ni-Ga alloys show similar trends to Ni 2 MnGa alloys in both their dependence of martensitic transformation temperatures on electron concentration and saturation magnetization [2,5]. However, unlike Ni 2 MnGa alloys which are single phase over a large compositional range [6], recent phase equilibria investigations [3,4] have reported that Co 2 NiGa alloys with transformations near room temperature lie within a twophase field, similar to the Co-Ni-Al alloys [4,7,8]. This major difference in phase equilibria imposes significant limitations on the synthesis of single crystals as well as subsequent annealing and training of the martensitic transformation.…”

Section: Introductionmentioning

confidence: 93%

“…The recent investigations of shape memory transformations in Co-Ni-Ga alloys [1][2][3][4] have reported shape memory behavior comparable to those associated with other ternary Heusler alloys such as Ni 2 MnGa. Initial measurements on Co-Ni-Ga alloys show similar trends to Ni 2 MnGa alloys in both their dependence of martensitic transformation temperatures on electron concentration and saturation magnetization [2,5].…”

Section: Introductionmentioning

confidence: 99%

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Phase Stability of Single Crystalline Co-Ni-Ga Shape Memory Alloy

2003

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Single crystals of Co 48 Ni 22 Ga 30 have been synthesized using a modified Bridgman method. The ability to solidify and retain single phase B2 austenite was found to depend not only on the starting composition and growth rate, but also the ability to maintain sufficiently high cooling rates to avoid the precipitation of a Corich FCC phase during post-solidification cooling. DSC measurements on the single crystal found the M s , M f , A s , and A f to be 35.7°C, -1.8°C, 34.1°C and 72.2°C, respectively. On subsequent heating the B2 phase was found to partially decompose into the Co-rich phase at temperatures exceeding 380°C. Decomposition of the single phase B2 phase was tracked by microstructural observation, DSC, powder diffraction and low temperature heat capacity measurement. Restoration of the crystal to single phase B2 austenite required annealing of the crystal at temperatures above 1125°C followed by rapid cooling. 22 Ga 30 have been synthesized using a modified Bridgman method. The ability to solidify and retain single phase B2 austenite was found to depend not only on the starting composition and growth rate, but also the ability to maintain sufficiently high cooling rates to avoid the precipitation of a Co-rich FCC phase during post-solidification cooling. DSC measurements on the single crystal found the M s , M f , A s , and A f to be 35.7°C, -1.8°C, 34.1°C and 72.2°C, respectively. On subsequent heating the B2 phase was found to partially decompose into the Co-rich phase at temperatures exceeding 380°C. Decomposition of the single phase B2 phase was tracked by microstructural observation, DSC, powder diffraction and low temperature heat capacity measurement. Restoration of the crystal to single phase B2 austenite required annealing of the crystal at temperatures above 1125°C followed by rapid cooling.

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Section: Introductionmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

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Phase Stability of Single Crystalline Co-Ni-Ga Shape Memory Alloy

2003

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“…Therefore, in the past few years, there has been more research invested in the search for materials exhibiting the MSM effect and having more favorable mechanical properties at the same time. Over the past few years, other MSM alloys, such as Fe-Pt, 8 Fe-Pd, 9 CoNi-Al, 10 Co-Ni-Ga, 11 Fe-Ni-Ga, 12 and Ni-Mn-Al, [13][14][15][16] have been encountered.…”

Section: Introductionmentioning

confidence: 99%

Martensitic transitions and the nature of ferromagnetism in the austenitic and martensitic states ofNi−Mn−Snalloys

et al. 2005

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Structural and magnetic transformations in the Heusler-based system Ni 0.50 Mn 0.50−x Sn x are studied by x-ray diffraction, optical microscopy, differential scanning calorimetry, and magnetization. The structural transformations are of austenitic-martensitic character. The austenite state has an L2 1 structure, whereas the structures of the martensite can be 10M, 14M, or L1 0 depending on the Sn composition. For samples that undergo martensitic transformations below and around room temperature, it is observed that the magnetic exchange in both parent and product phases is ferromagnetic, but the ferromagnetic exchange, characteristic of each phase, is found to be of different strength. This gives rise to different Curie temperatures for the austenitic and martensitic states.

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“…[7][8][9] Promising candidates for a thermoelastic transformation in the ferromagnetic state are Co 2 Ni͑Al, Ga͒. In these materials the Mn atoms have been replaced by Ni to circumvent the problems arising from antiferromagnetic interactions in the material.…”

Section: Introductionmentioning

confidence: 99%

Electronic structure and lattice dynamics of the magnetic shape-memory alloyCo2NiGa

et al. 2010

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In addition to the prototypical Ni-Mn-based Heusler alloys, the Co-Ni-Ga systems have recently been suggested as another prospective materials class for magnetic shape-memory applications. We provide a characterization of the dynamical properties of this material and their relation to the electronic structure within a combined experimental and theoretical approach. This relies on inelastic neutron scattering to obtain the phonon dispersion while first-principles calculations provide the link between dynamical properties and electronic structure. In contrast to Ni 2 MnGa, where the softening of the TA 2 phonon branch is related to Fermi-surface nesting, our results reveal that the respective anomalies are absent in Co-Ni-Ga, in the phonon dispersions as well as in the electronic structure. Keywords Materials Science and Engineering Disciplines Condensed Matter Physics | Materials Science and Engineering CommentsThis article is from Physical Review B 82 (2010) In addition to the prototypical Ni-Mn-based Heusler alloys, the Co-Ni-Ga systems have recently been suggested as another prospective materials class for magnetic shape-memory applications. We provide a characterization of the dynamical properties of this material and their relation to the electronic structure within a combined experimental and theoretical approach. This relies on inelastic neutron scattering to obtain the phonon dispersion while first-principles calculations provide the link between dynamical properties and electronic structure. In contrast to Ni 2 MnGa, where the softening of the TA 2 phonon branch is related to Fermisurface nesting, our results reveal that the respective anomalies are absent in Co-Ni-Ga, in the phonon dispersions as well as in the electronic structure.

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Phase Equilibria and Phase Transformations in New B2-type Ferromagnetic Shape Memory Alloys of Co-Ni-Ga and Co-Ni-Al Systems

Cited by 270 publications

References 12 publications

Phase Stability of Single Crystalline Co-Ni-Ga Shape Memory Alloy

Phase Stability of Single Crystalline Co-Ni-Ga Shape Memory Alloy

Martensitic transitions and the nature of ferromagnetism in the austenitic and martensitic states ofNi−Mn−Snalloys

Electronic structure and lattice dynamics of the magnetic shape-memory alloyCo2NiGa

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