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16 pages, 3726 KiB

Open AccessArticle

Characterizing Changes in Grain Growth, Mechanical Properties, and Transformation Properties in Differently Sintered and Annealed Binder-Jet 3D Printed 14M Ni–Mn–Ga Magnetic Shape Memory Alloys

by Aaron Acierno, Amir Mostafaei, Jakub Toman, Katerina Kimes, Mirko Boin, Robert C. Wimpory, Ville Laitinen, Andrey Saren, Kari Ullakko and Markus Chmielus

Metals 2022, 12(5), 724; https://doi.org/10.3390/met12050724 - 24 Apr 2022

Cited by 3 | Viewed by 2167

Abstract

Ni–Mn–Ga Heusler alloys are multifunctional materials that demonstrate macroscopic strain under an externally applied magnetic field through the motion of martensite twin boundaries within the microstructure. This study sought to comprehensively characterize the microstructural, mechanical, thermal, and magnetic properties near the solidus in [...] Read more.

Ni–Mn–Ga Heusler alloys are multifunctional materials that demonstrate macroscopic strain under an externally applied magnetic field through the motion of martensite twin boundaries within the microstructure. This study sought to comprehensively characterize the microstructural, mechanical, thermal, and magnetic properties near the solidus in binder-jet 3D printed 14M Ni₅₀Mn₃₀Ga₂₀. Neutron diffraction data were analyzed to identify the martensite modulation and observe the grain size evolution in samples sintered at temperatures of 1080 °C and 1090 °C. Large clusters of high neutron-count pixels in samples sintered at 1090 °C were identified, suggesting Bragg diffraction of large grains (near doubling in size) compared to 1080 °C sintered samples. The grain size was confirmed through quantitative stereology of polished surfaces for differently sintered and heat-treated samples. Nanoindentation testing revealed a greater resistance to plasticity and a larger elastic modulus in 1090 °C sintered samples (relative density ~95%) compared to the samples sintered at 1080 °C (relative density ~80%). Martensitic transformation temperatures were lower for samples sintered at 1090 °C than 1080 °C, though a further heat treatment step could be added to tailor the transformation temperature. Microstructurally, twin variants ≤10 μm in width were observed and the presence of magnetic anisotropy was confirmed through magnetic force microscopy. This study indicates that a 10 °C sintering temperature difference can largely affect the microstructure and mechanical properties (including elastic modulus and hardness) while still allowing for the presence of magnetic twin variants in the resulting modulated martensite. Full article

(This article belongs to the Special Issue Recent Development in Magnetic Shape Memory Alloys)

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10 pages, 19550 KiB

Open AccessFeature PaperArticle

Elastocaloric and Magnetocaloric Effects Linked to the Martensitic Transformation in Bulk Ni₅₅Fe₁₁Mn₇Ga₂₇ Alloys Produced by Arc Melting and Spark Plasma Sintering

by J. D. Navarro-García, J. P. Camarillo-Garcia, F. Alvarado-Hernández, J. L. Sánchez Llamazares and H. Flores-Zúñiga

Metals 2022, 12(2), 273; https://doi.org/10.3390/met12020273 - 02 Feb 2022

Cited by 2 | Viewed by 1792

Abstract

The investigation of caloric effects linked to first-order structural transitions in Heusler-type alloys has become a subject of considerable current interest due to their potential utilization as refrigerants in solid-state cooling devices. This study is mainly motivated by the possibility of developing refrigeration [...] Read more.

The investigation of caloric effects linked to first-order structural transitions in Heusler-type alloys has become a subject of considerable current interest due to their potential utilization as refrigerants in solid-state cooling devices. This study is mainly motivated by the possibility of developing refrigeration devices of improved energy efficiency with a reduced environmental impact. We produced partially textured and isotropic bulk samples of the Heusler-type magnetic shape memory alloy Ni₅₅Fe₁₁Mn₇Ga₂₇ by arc melting and spark plasma sintering (SPS), respectively. Their structural, microstructural, and phase transition characteristics and magnetocaloric and elastocaloric effects, associated with first-order martensitic transformation (MT), were studied. The elemental chemical compositions of both samples were close to nominal, and a martensitic-like structural transformation appeared around room temperature with similar starting and finishing structural transition temperatures. At room temperature, austenite exhibited a highly ordered L2₁-type crystal structure. The partial grain orientation and isotropic nature of the arc-melted and SPS samples, respectively, were revealed by X-ray diffraction and SEM observations of the microstructure. For the arc-melted sample, austenite grains preferentially grew in the (100) direction parallel to the thermal gradient during solidification. The favorable effect of the texture on the elastocaloric response was demonstrated. Finally, due to its partial grain orientation, the arc-melted bulk sample showed superior values of maximum magnetic entropy change (|ΔS_M|^max = 18.6 Jkg⁻¹K⁻¹ at 5 T) and elastocaloric adiabatic temperature change (|ΔT_ad^me|^max = 2.4 K at 120 MPa) to those measured for the SPS sample (|ΔS_M|^max = 8.5 Jkg⁻¹K⁻¹ and (|ΔT_ad^me|^max = 0.8 K). Full article

(This article belongs to the Special Issue Recent Development in Magnetic Shape Memory Alloys)

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8 pages, 1167 KiB

Open AccessFeature PaperArticle

Compositional Dependence of Magnetocrystalline Anisotropy in Fe-, Co-, and Cu-Alloyed Ni-Mn-Ga

by Michal Rameš, Vít Kopecký and Oleg Heczko

Metals 2022, 12(1), 133; https://doi.org/10.3390/met12010133 - 11 Jan 2022

Cited by 4 | Viewed by 1361

Abstract

The key for the existence of magnetic induced reorientation is strong magnetocrystalline anisotropy, i.e., the coupling between ferroelastic and ferromagnetic ordering. To increase the transformation temperatures and thus functionality, various elemental alloying in Ni-Mn-Ga is tried. We analyzed more than twenty polycrystalline alloys [...] Read more.

The key for the existence of magnetic induced reorientation is strong magnetocrystalline anisotropy, i.e., the coupling between ferroelastic and ferromagnetic ordering. To increase the transformation temperatures and thus functionality, various elemental alloying in Ni-Mn-Ga is tried. We analyzed more than twenty polycrystalline alloys alloyed by small amount (up to 5atom%) of transitional metals Co, Fe, Ni, and Cu for the value of magnetic anisotropy in search of general trends with alloying. In agreement with previous reports, we found that maximum anisotropy occurs at stoichiometric Ni₂MnGa and any alloying decreases its value. The strongest decrease of the anisotropy is observed in the case where the alloyed elements substitute Ga. Full article

(This article belongs to the Special Issue Recent Development in Magnetic Shape Memory Alloys)

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8 pages, 1379 KiB

Open AccessArticle

Neutron Diffraction Study of the Martensitic Transformation of Ni_2.07Mn_0.93Ga Heusler Alloy

by Lara Righi

Metals 2021, 11(11), 1749; https://doi.org/10.3390/met11111749 - 31 Oct 2021

Cited by 1 | Viewed by 1664

Abstract

The martensitic transition featuring the ternary Heusler alloy Ni2.09Mn0.91Ga was investigated by neutron diffraction. Differential scanning calorimetry indicated that structural transition starts at 230 K on cooling with a significant increase in the martensitic transformation onset compared to the classical Ni2MnGa. The low-temperature [...] Read more.

The martensitic transition featuring the ternary Heusler alloy Ni2.09Mn0.91Ga was investigated by neutron diffraction. Differential scanning calorimetry indicated that structural transition starts at 230 K on cooling with a significant increase in the martensitic transformation onset compared to the classical Ni2MnGa. The low-temperature martensite presents the 5M type of modulated structure, and the structural analysis was performed by the application of the superspace approach. As already observed in Mn-rich modulated martensites, the periodical distortion corresponds to an incommensurate wave-like shift of the atomic layers. The symmetry of the modulated martensite at 220 K is orthorhombic with unit cell constants a = 4.2172(3) Å, b = 5.5482(2) Å, and c = 4.1899(2) Å; space group Immm(00γ)s00; and modulation vector q = γc* = 0.4226(5)c*. Considering the different neutron scattering lengths of the elements involved in this alloy, it was possible to ascertain that the chemical composition was Ni2.07Mn0.93Ga, close to the nominal formula. In order to characterize the martensitic transformation upon increasing the temperature, a series of neutron diffraction patterns was collected at different temperatures. The structural analysis indicated that the progressive change of the martensitic lattice is characterized by the exponential change of the c/a parameter approaching the limit value c/a = 1 of the cubic austenite. Full article

(This article belongs to the Special Issue Recent Development in Magnetic Shape Memory Alloys)

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18 pages, 3617 KiB

Open AccessFeature PaperArticle

Transitory Ultrasonic Absorption in “Domain Engineered” Structures of 10 M Ni-Mn-Ga Martensite

by Sergey Kustov, Andrey Saren, Bruno D’Agosto, Konstantin Sapozhnikov, Vladimir Nikolaev and Kari Ullakko

Metals 2021, 11(10), 1505; https://doi.org/10.3390/met11101505 - 23 Sep 2021

Cited by 2 | Viewed by 1451

Abstract

In this work we create in 10 M Ni-Mn-Ga martensitic samples special martensitic variant structures consisting of only three twins separated by two a/c twin boundaries: Type I and Type II, with relatively low and very high mobility, respectively. The “domain engineered” structure [...] Read more.

In this work we create in 10 M Ni-Mn-Ga martensitic samples special martensitic variant structures consisting of only three twins separated by two a/c twin boundaries: Type I and Type II, with relatively low and very high mobility, respectively. The “domain engineered” structure thus created allows us to investigate the dynamics of a single highly mobile a/c twin boundary (TB). We show that temperature variations between 290 and 173 K in our samples induce an intense transitory internal friction at ultrasonic frequencies ca. 100 kHz, peaking around 215 K. A comparison is made of the data for the “domain engineered” sample with the behaviour of reference samples without a/c TB. Reference samples have two different orientations of a/b twins providing zero and maximum shear stresses in a/b twinning planes. We argue, first, that the transitory internal friction, registered at rather high ultrasonic frequencies, has magnetic origin. It is related with the rearrangement of magnetic domain structure due to the motion of a/c twin boundary induced by thermal stresses. This internal friction term can be coined “magnetic transitory internal friction”. Magnetic transitory internal friction is a new category, linking the classes of transitory and magnetomechanical internal friction. Second, the structure of a/b twins is strongly non-equilibrium over a broad temperature range. As a consequence, the Young’s modulus values of the samples with maximum shear stress in a/b twinning planes can take any value between ca. 15 and 35 GPa, depending on the prehistory of the sample. Full article

(This article belongs to the Special Issue Recent Development in Magnetic Shape Memory Alloys)

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14 pages, 2750 KiB

Open AccessArticle

A Ternary Map of Ni–Mn–Ga Heusler Alloys from Ab Initio Calculations

by Yulia Sokolovskaya, Olga Miroshkina, Danil Baigutlin, Vladimir Sokolovskiy, Mikhail Zagrebin, Vasilly Buchelnikov and Alexey T. Zayak

Metals 2021, 11(6), 973; https://doi.org/10.3390/met11060973 - 17 Jun 2021

Cited by 5 | Viewed by 1841

Abstract

In the search for new magnetic functional materials, non-stoichiometric compounds remain a relatively unexplored territory. While experimentalists create new compositions looking for improved functional properties, their work is not guided by systematic theoretical predictions. Being designed for perfect periodic crystals, the majority of [...] Read more.

In the search for new magnetic functional materials, non-stoichiometric compounds remain a relatively unexplored territory. While experimentalists create new compositions looking for improved functional properties, their work is not guided by systematic theoretical predictions. Being designed for perfect periodic crystals, the majority of first-principles approaches struggle with the concept of a non-stoichiometric system. In this work, we attempt a systematic computational study of magnetic and structural properties of Ni–Mn–Ga, mapped onto ternary composition diagrams. Compositional stability was examined using the convex hull analysis. We show that the cubic austenite has its stability region close to the stoichiometric Ni

_{2}

MnGa, in agreement with experimental data, while the tetragonal martensite spreads its stability over a wider range of Mn and Ni contents. The unstable compositions in both austenite and martensite states are located in the Ga-rich corner of the ternary diagram. We note that simultaneous stability of the austenite and martensite should be considered for potentially stable compounds suitable for synthesis. The majority of compounds are predicted to be ferrimagnetically ordered in both austenitic and martensitic states. The methodology used in this work is computationally tractable, yet it delivers some predictive power. For experimentalists who plan to synthesize stable Ni–Mn–Ga compounds with ferromagnetic order, we narrow the target compositional range substantially. Full article

(This article belongs to the Special Issue Recent Development in Magnetic Shape Memory Alloys)

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11 pages, 9284 KiB

Open AccessFeature PaperArticle

Temperature Dependent Stress–Strain Behavior and Martensite Stabilization in Magnetic Shape Memory Ni_51.1Fe_16.4Ga_26.3Co_6.2 Single Crystal

by Patricia Lázpita, Elena Villa, Francesca Villa and Volodymyr Chernenko

Metals 2021, 11(6), 920; https://doi.org/10.3390/met11060920 - 04 Jun 2021

Cited by 5 | Viewed by 1825

Abstract

The superelastic properties and stress-induced martensite (SIM) stabilization have been studied in a shape memory Ni_51.1Fe_16.4Ga_26.3Co_6.2 single crystal. The single crystal, characterized by a thermally induced forward martensitic transformation temperature around 56 °C in the initial [...] Read more.

The superelastic properties and stress-induced martensite (SIM) stabilization have been studied in a shape memory Ni_51.1Fe_16.4Ga_26.3Co_6.2 single crystal. The single crystal, characterized by a thermally induced forward martensitic transformation temperature around 56 °C in the initial state, has been submitted to compression mechanical testing at different temperatures well above, near and below the martensitic transformation (MT). After each mechanical test, the characteristic MT temperatures and the transformation enthalpy have been monitored by means of differential scanning calorimetry. At temperatures below MT, the stress–strain (σ–ε) curves show a large strain, around 6.0%, resulting from the detwinning process in the martensitic microstructure, which remains accumulated after unloading in the detwinned state of the sample as a typical behavior of the shape memory alloys (SMAs). After just two “σ–ε + heating” cycles the accumulation of strain was not observed any more indicating the formation of a two-way shape memory effect which consists in a spontaneous recovery of the aforementioned detwinned state of the sample during its cooling across the forward MT. Whereas the thermally induced shape recovery in conventional SMAs occurs at the fixed value of the reverse MT temperature, the heating DSC curves of the mechanically deformed martensite in the present work show a burst-like calorimetric peak at the reverse MT arising at temperatures essentially higher than the thermally activated one. This behavior is the result of the SIM stabilization effect. After a short thermal aging in the stress-free state, this effect almost disappears, showing a slight impact on the MT characteristic temperatures and the enthalpy. At temperatures higher than the transformation one, the SIM is not stabilized, as the mechanically induced martensite fully retransforms into austenite after the unloading. From the σ–ε curves, the critical stress, σ_c, as well as the values of Young’s moduli of martensite and austenite are determined showing linear dependences on the temperature with a slope of 3.6 MPa/°C. Full article

(This article belongs to the Special Issue Recent Development in Magnetic Shape Memory Alloys)

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18 pages, 1235 KiB

Open AccessArticle

Full Variation of Site Substitution in Ni-Mn-Ga by Ferromagnetic Transition Metals

by Vít Kopecký, Michal Rameš, Petr Veřtát, Ross H. Colman and Oleg Heczko

Metals 2021, 11(6), 850; https://doi.org/10.3390/met11060850 - 21 May 2021

Cited by 12 | Viewed by 2261

Abstract

Systematic doping by transition elements Fe, Co and Ni on each site of Ni₂MnGa alloy reveal that in bulk material the increase in martensitic transformation temperature is usually accompanied by the decrease in ferromagnetic Curie temperature, and vice versa. The highest [...] Read more.

Systematic doping by transition elements Fe, Co and Ni on each site of Ni₂MnGa alloy reveal that in bulk material the increase in martensitic transformation temperature is usually accompanied by the decrease in ferromagnetic Curie temperature, and vice versa. The highest martensitic transformation temperature (571 K) was found for Ni_50.0Mn_25.4(Ga_20.3Ni_4.3) with the result of a reduction in Curie temperature by 55 K. The highest Curie point (444 K) was found in alloy (Ni_44.9Co_5.1)Mn_25.1Ga_24.9; however, the transition temperature was reduced to 77 K. The dependence of transition temperature is better scaled with the N_e/a parameter (number of non-bonding electrons per atom) compared to usual e/a (valence electrons per atom). N_e/a dependence predicts a disappearance of martensitic transformation in (Ni_45.3Fe_5.3)Mn_23.8Ga_25.6, in agreement with our experiment. Although Curie temperature usually slightly decreases while the martensitic transition increases, there is no significant correlation of Curie temperature with e/a or N_e/a parameters. The doping effect of the same element is different for each compositional site. The cascade substitution is discussed and related to the experimental data. Full article

(This article belongs to the Special Issue Recent Development in Magnetic Shape Memory Alloys)

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14 pages, 4677 KiB

Open AccessFeature PaperArticle

Actuating a Magnetic Shape Memory Element Locally with a Set of Coils

by Andrew Armstrong and Peter Müllner

Metals 2021, 11(4), 536; https://doi.org/10.3390/met11040536 - 25 Mar 2021

Viewed by 1703

Abstract

The local actuation of a magnetic shape memory (MSM) element as used in an MSM micropump is considered. This paper presents the difference between an electromagnetic driver and a driver that uses a rotating permanent magnet. For the magnetic field energy of the [...] Read more.

The local actuation of a magnetic shape memory (MSM) element as used in an MSM micropump is considered. This paper presents the difference between an electromagnetic driver and a driver that uses a rotating permanent magnet. For the magnetic field energy of the permanent magnetic drive, the element takes in a significant stray field. In a particular case, energy reduction was 12.7 mJ. For an electromagnetic drive with an identical size of the MSM element, the total magnetic field energy created by the system was 2.28 mJ. Attempts to experimentally nucleate twins in an MSM element by energizing an electromagnetic drive failed even though the local magnetic field exceeded the magnetic switching field. The energy variation is an order of magnitude smaller for the electromagnetic drive, and it does not generate the necessary driving force. It was assumed in previous work that the so-called magnetic switching field presents a sufficient requirement to nucleate a twin and, thus, to locally actuate an MSM element. Here, we show that the total magnetic field energy available to the MSM element presents another requirement. Full article

(This article belongs to the Special Issue Recent Development in Magnetic Shape Memory Alloys)

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14 pages, 3933 KiB

Open AccessArticle

External-Field-Induced Phase Transformation and Associated Properties in a Ni₅₀Mn₃₄Fe₃In₁₃ Metamagnetic Shape Memory Wire

by Zhen Chen, Daoyong Cong, Shilei Li, Yin Zhang, Shaohui Li, Yuxian Cao, Shengwei Li, Chao Song, Yang Ren and Yandong Wang

Metals 2021, 11(2), 309; https://doi.org/10.3390/met11020309 - 10 Feb 2021

Cited by 4 | Viewed by 1890

Abstract

Metamagnetic shape memory alloys exhibit a series of intriguing multifunctional properties and have great potential for applications in magnetic actuation, sensing and magnetic refrigeration. However, the poor mechanical properties of these alloys with hardly any tensile deformability seriously limit their practical application. In [...] Read more.

Metamagnetic shape memory alloys exhibit a series of intriguing multifunctional properties and have great potential for applications in magnetic actuation, sensing and magnetic refrigeration. However, the poor mechanical properties of these alloys with hardly any tensile deformability seriously limit their practical application. In the present work, we developed a Ni-Fe-Mn-In microwire that exhibits both a giant, tensile superelasticity and a magnetic-field-induced first-order phase transformation. The recoverable strain of superelasticity is more than 20% in the temperature range of 233–283 K, which is the highest recoverable strain reported heretofore in Ni-Mn-based shape memory alloys (SMAs). Moreover, the present microwire exhibits a large shape memory effect with a recoverable strain of up to 13.9% under the constant tensile stress of 225 MPa. As a result of the magnetic-field-induced first-order phase transformation, a large reversible magnetocaloric effect with an isothermal entropy change ΔS_m of 15.1 J kg⁻¹ K⁻¹ for a field change from 0.2 T to 5 T was achieved in this microwire. The realization of both magnetic-field and tensile-stress-induced transformations confers on this microwire great potential for application in miniature multi-functional devices and provides an opportunity for multi-functional property optimization under coupled multiple fields. Full article

(This article belongs to the Special Issue Recent Development in Magnetic Shape Memory Alloys)

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Review

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21 pages, 1955 KiB

Open AccessReview

Neutron Scattering as a Powerful Tool to Investigate Magnetic Shape Memory Alloys: A Review

by Natalia A. Río-López, Patricia Lázpita, Daniel Salazar, Viktor I. Petrenko, Fernando Plazaola, Volodymyr Chernenko and Jose M. Porro

Metals 2021, 11(5), 829; https://doi.org/10.3390/met11050829 - 18 May 2021

Cited by 8 | Viewed by 3812

Abstract

Magnetic shape memory alloys (MSMAs) are an interesting class of smart materials characterized by undergoing macroscopic deformations upon the application of a pertinent stimulus: temperature, stress and/or external magnetic fields. Since the deformation is rapid and contactless, these materials are being extensively investigated [...] Read more.

Magnetic shape memory alloys (MSMAs) are an interesting class of smart materials characterized by undergoing macroscopic deformations upon the application of a pertinent stimulus: temperature, stress and/or external magnetic fields. Since the deformation is rapid and contactless, these materials are being extensively investigated for a plethora of applications, such as sensors and actuators for the medical, automotive and space industries, energy harvesting and damping devices, among others. These materials also exhibit a giant magnetocaloric effect, whereby they are very promising for magnetic refrigeration. The applications in which they can be used are extremely dependent on the material properties, which are, in turn, greatly conditioned by the structure, atomic ordering and magnetism of a material. Particularly, exploring the material structure is essential in order to push forward the current application limitations of the MSMAs. Among the wide range of available characterization tools, neutron scattering techniques stand out in acquiring advanced knowledge about the structure and magnetism of these alloys. Throughout this manuscript, a comprehensive review about the characterization of MSMAs using neutron techniques is presented. Several elastic neutron scattering techniques will be explained and exemplified, covering neutron imaging techniques—such as radiography, tomography and texture diffractometry; diffraction techniques—magnetic (polarized neutron) diffraction, powder neutron diffraction and single crystal neutron diffraction, reflectometry and small angle neutron scattering. This will be complemented with a few examples where inelastic neutron scattering has been employed to obtain information about the phonon dispersion in MSMAs. Full article

(This article belongs to the Special Issue Recent Development in Magnetic Shape Memory Alloys)

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