Chemical segregation during bulk single crystal preparation of Ni–Mn–Ga ferromagnetic shape memory alloys

Schlagel, Deborah L.; Wu, Yuehong; Zhang, W; Lograsso, Thomas A.

doi:10.1016/s0925-8388(00)01161-0

Cited by 138 publications

(73 citation statements)

References 9 publications

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“…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: 75%

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: 75%

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

2003

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“…Nonuniformities in concentration are often due to crystal growth and may lead to significant variation in structure, transformation temperature, and thus in mechanical properties. [45][46][47] Different amounts of nanotwins may have been present at the beginning of the deformation experiments. These nanotwins may have caused microplasticity, which would affect the slope of the linear region.…”

Section: Discussionmentioning

confidence: 99%

Deformation twinning in Ni–Mn–Ga micropillars with 10M martensite

Reinhold

Kiener

Knowlton

et al. 2009

Journal of Applied Physics

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The maximum actuation frequency of magnetic shape-memory alloys ͑MSMAs͒ significantly increases with decreasing size of the transducer making MSMAs interesting candidates for small scale actuator applications. To study the mechanical properties of Ni-Mn-Ga single crystals on small length scales, two single-domain micropillars with dimensions of 10ϫ 15ϫ 30 m 3 were fabricated from a Ni-Mn-Ga monocrystal using dual beam focused ion beam machining. The pillars were oriented such that the crystallographic c direction was perpendicular to the loading direction. The pillars were compressed to maximum stresses of 350 and 50 MPa, respectively. Atomic force microscopy and magnetic force microscopy were performed prior to fabrication of the pillars and following the deformation experiments. Both micropillars were deformed by twinning as evidenced by the stress-strain curve. For one pillar, a permanent deformation of 3.6% was observed and ac twins ͑10M martensite͒ were identified after unloading. For the other pillar, only 0.7% remained upon unloading. No twins were found in this pillar after unloading. The recovery of deformation is discussed in the light of pseudoelastic twinning and twin-substrate interaction. The twinning stress was higher than in similar macroscopic material. However, further studies are needed to substantiate a size effect.

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“…Это превращение протекает в сплаве вплоть до температуры 1070 K. Согласно литературным данным, в сплавах исследуемой системы в этой области темпе-ратур наблюдается фазовое превращение (при нагреве образца) упорядоченной фазы L2 1 в разупорядоченную фазу B2 [32][33][34]. Второй эндотермический пик на кривой ДСК при температуре 1426 K показывает достаточно большое поглощение теплоты.…”

Section: экспериментальные результатыunclassified

Влияние температуры деформации осадкой на формирование мелкозернистой структуры литого сплава системы Ni-Mn-Ga

Musabirov¹,

Safarov²,

Sharipov³

et al. 2017

Физика Твердого Тела

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Исследованы пластическое поведение в процессе деформации осадкой и ее влияние на микрострук-туру в поликристаллическом сплаве Ni 2.19 Fe 0.04 Mn 0.77 Ga. Методом анализа температурной зависимости удельной намагниченности установлены температуры мартенситного и магнитного фазовых превращений, которые имеют следующие значения: MF = 320 K, AS = 360 K, TC = 380 K. С помощью дифференциально-сканирующей калориметрии показано, что при нагреве образца в интервале температур 930−1070 K в сплаве наблюдается фазовый переход из упорядоченной фазы L2 1 в разупорядоченную фазу B2. Температура плавления составляет 1426 K. Анализ диаграмм нагружения, построенных при осаждении образца при температурах 773, 873 и 973 K, показывает, что при температуре 773 K поведение кривой напряжение−деформация свойственно холодной деформации. Характер кривых зависимости для температур 873 и 973 K типичен для горячей деформации. После деформации сплава исследована его микроструктура с помощью сканирующей электронной микроскопии в режиме обратно отраженных электронов. Пластическая деформация сплава при исследуемых температурах приводит к фрагментации зеренной структуры в области локализованной деформации. При всех температурах наблюдается рекристаллизованная зеренная структура. Установлено, что после осадки при 973 K наблюдается неравномерная рекристаллизация структуры вследствие интенсивности этого процесса при столь высокой температуре. Наиболее однородной по среднему размеру зерен является микроструктура сплава после пластической деформации при температуре 873 K.Деформационно-термическая обработка сплава, дифференциально-сканирующая калориметрия и исследо-вание микроструктуры материала выполнены при финансовой поддержке РФФИ в рамках научного проекта № 16-32-60159 мол_а_дк. Выплавка сплава и анализ фазовых превращений в области комнатных температур выполнены при поддержке РНФ, грант №14-22-00279.

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Chemical segregation during bulk single crystal preparation of Ni–Mn–Ga ferromagnetic shape memory alloys

Cited by 138 publications

References 9 publications

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

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

Deformation twinning in Ni–Mn–Ga micropillars with 10M martensite

Влияние температуры деформации осадкой на формирование мелкозернистой структуры литого сплава системы Ni-Mn-Ga

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