Effects of pre-deformation on the martensitic transformation and magnetocaloric property in Ni-Mn-Co-Sn ribbons
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This paper investigates the martensitic transformation and magnetocaloric effect in pre-deformed Ni-Mn-Co-Sn ribbons. The experimental results show that the reverse martensitic transformation temperature TM increases with the increasing pre-pressure, suggesting that pre-deformation is another effective way to adjust TM in ferromagnetic shape memory alloys. Large magnetic entropy changes and refrigerant capacities are obtained in these ribbons as well. It also discusses the origin of the enhanced martensitic transformation temperature and magnetocaloric property in pre-deformed Ni-Mn-Co-Sn ribbons.Keywords:
Magnetic refrigeration
Diffusionless transformation
Nickel titanium
Diffusionless transformation
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The martensitic magnetothermoelastic transformation induced by a magnetic field in FSMA has been studied. It has been observed that the shape memory effect is associated with the reversible magnetic field‐induced martensite at higher temperatures. It has been noted that upon cooling from the high temperature austenite parent phase the ferromagnetic shape memory alloys exhibit transition from paramagnetism to ferromagnetism. The Ni‐25Mn‐25Ga (at%) shows the thermomechanical martensitic transformation. The micrograph shows the martensitic transformation of the alloy that strongly depends on the applied magnetic field. The mechanisms of the magnetic microstructure causes the martensite bands, which run diagonally from left to right in the micrograph, have been observed. It is proposed that the FSMAs are very promising candidates for biomedical applications as the new smart material.
Magnetic shape-memory alloy
Diffusionless transformation
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Magnetic and martensitic transition behaviors of a Ni46Mn41In13 Heusler alloy were investigated by differential scanning calorimetry and vibrating sample magnetometry. A unique martensitic transition from the ferromagnetic austenite phase to the antiferromagneticlike martensite phase was detected and magnetic-field-induced “reverse” transition was confirmed in a high magnetic field. In addition, a large positive magnetic entropy change, which reached 13J∕kgK at 9T, was observed to accompany reverse martensitic transition. This alloy shows promise as a metamagnetic shape memory alloy with magnetic-field-induced shape memory effect and as a magnetocaloric material.
Magnetic refrigeration
Magnetic shape-memory alloy
Diffusionless transformation
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Considering that the magnetic field-induced strain in ferromagnetic shape memory alloys arises from the field-induced motion of twin boundaries in the martensite state, a thermo-magneto-mechanical coupled model of ferromagnetic shape memory alloys is presented, which captures the ferromagnetic shape memory effect, hysteresis effect i.e. In the model, considering the effects of thermo-magneto-mechanical energy, which govern the process of martensitic variant reorientation, we give the simulations of magneto-mechanical-induced strain effect and feature.
Hysteresis
Magnetic shape-memory alloy
Diffusionless transformation
Magneto
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Diffusionless transformation
Magnetic shape-memory alloy
Valence electron
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The realization of forward martensitic transformation under isothermal conditions in NiTi-based alloys has been well studied experimentally, along with the kinetics of this process. However, existing models do not allow the isothermal martensite volume fraction ΦM to be estimated, hence the influence of holding temperature or time on the ΦM value could not be calculated. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory is normally used to describe isothermal kinetics, but it has not been applied for martensite transformation, which occurs in shape-memory alloys during holding at a constant temperature. Thus, the aim of the present study is to adapt the JMAK theory and use to estimate ΦM variation with time during holding of Ti40.7Hf9.5Ni44.8Cu5 alloy at different temperatures. The JMAK equation allows the variation of the isothermal martensite volume fraction with time during holding at constant temperatures to be approximated. It was applied to estimate experimental ΦM(t) curves in Ti40.7Hf9.5Ni44.8Cu5 alloy and a good approximation was established. The dependencies of JMAK-like equation parameters on the holding temperature were also found and approximated. Thus, the expression for the dependence of the isothermal martensite volume fraction on holding temperature and time was found and calculation of the ΦM(t) curves was carried out. The simulated and experimental data for the Ti40.7Hf9.5Ni44.8Cu5 shape memory alloy were shown to be in good agreement.
Isothermal process
Volume fraction
Isothermal transformation diagram
Diffusionless transformation
Constant (computer programming)
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The ferromagnetic shape memory alloy ribbons with composition Ni45Co5Mn38Sn12 are shown to have field induced kinetically arrested ferromagnetic austenite phase down to the low temperature due to hindered martensite transformation. This gives rise to the coexisting martensite and austenite phases in a wide range of temperature and field. Here, we show a systematic rise in arrested austenite phase with the reduction in martensite phase quantitatively by various magnetization measurements. The fraction of these coexisting phases can be tuned in “field-temperature” space. Further, we show that the “domain” of tunability varies with temperature.
Magnetic shape-memory alloy
Diffusionless transformation
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Diffusionless transformation
Hysteresis
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A series of high-Mn content Mn47+xNi43−xSn10 (x=0, 1, 2, 3, 4, and 5) ferromagnetic shape memory alloys were prepared by arc melting method. The martensitic transformation were observed in these alloys, even the content of Mn is higher than 50 at. %. The phase transition temperature of these alloys can be adjusted by tuning the compositions of Ni and Mn. Large positive magnetic entropy change and negative magnetoresistance which originate from the magnetic-field-induced martensitic transformation are obtained in these alloys.
Magnetic refrigeration
Diffusionless transformation
Magnetic shape-memory alloy
Arc melting
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The martensitic thermoelastic and magnetic transformations have been investigated for the Ni–Mn–Ga ferromagnetic shape memory alloys. The martensitic phase of the shape memory alloy responds to the application of stress and, as a result, the martensite variants are rearranged to accommodate the applied stress, which results in the macroscopic shape change. The shape recovery property of Ni–24.7 Mn–24.8 Ga (at.%) alloy with martensitic transformation temperatures has been analysed. The mechanisms of the magnetic microstructure, which cause the martensite band domains and run diagonally in a micrograph from left to right, have been observed. The micrograph also shows that the martensitic transformation of Ni–24.7 Mn–24.8 Ga (at.%) alloy not only depends on the structural rearrangement but also responds to a magnetic field. It is observed that upon cooling from the high-temperature austenite parent phase, the ferromagnetic shape memory alloys exhibit transition from paramagnetism to ferromagnetism. It is studied that the Ni–Mn–Ga alloy is an intrinsically suitable ductile material.
Magnetic shape-memory alloy
Diffusionless transformation
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