Application of EBSD to the Crystallographic Investigation on Ni-Mn-Ga Alloys

For off-stoichiometric Ni2MnGa ferromagnetic shape memory alloys, a large shape change could be induced through the rearrangement of martensitic variants under an external magnetic field. Insight into the orientation relationships of martensitic variants and the characteristics of variant boundaries is thus essential for understanding the magnetic shape memory performance. In this paper, a thorough crystallographic investigation was made on the incommensurate 7M modulated martensite in one polycrystalline Ni50Mn30Ga20alloy by means of X-ray diffraction and SEM electron backscattered diffraction (EBSD). Locally, there are four differently-oriented martensitic variants, being twin related to one another. The twin interface planes are coherent and they are in coincidence with the respective twinning planes (K1). A primary exploration was performed to improve the microstructure by repeated magnetic field training during phase transition. The present investigation could offer useful guidance to develop specific technique for microstructure optimization.

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New approach to twin interfaces of modulated martensite

Journal of Applied Crystallography ◽

10.1107/s002188981000868x ◽

2010 ◽

Vol 43 (3) ◽

pp. 617-622 ◽

Cited By ~ 40

Author(s):

Zongbin Li ◽

Yudong Zhang ◽

Claude Esling ◽

Xiang Zhao ◽

Yandong Wang ◽

...

Keyword(s):

Shape Memory ◽

Electron Backscatter Diffraction ◽

Memory Performance ◽

Advanced Materials ◽

Orientation Relationships ◽

Ferromagnetic Shape Memory Alloys ◽

Interface Motion ◽

New Approach ◽

Martensitic Variant ◽

Martensitic Variants

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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Shape Memory Alloys: A Summary of Recent Achievements

Materials Science Forum ◽

10.4028/www.scientific.net/msf.583.21 ◽

2008 ◽

Vol 583 ◽

pp. 21-41 ◽

Cited By ~ 49

Author(s):

Peter Entel ◽

Vasiliy D. Buchelnikov ◽

Markus E. Gruner ◽

Alfred Hucht ◽

Vladimir V. Khovailo ◽

...

Keyword(s):

Magnetic Field ◽

External Magnetic Field ◽

Shape Memory ◽

Shape Change ◽

Heusler Alloys ◽

Systematic Change ◽

Magnetic Shape Memory ◽

Electronic Density ◽

Modulated Phases ◽

Modulated Structures

The Ni-Mn-Ga shape memory alloy displays the largest shape change of all known magnetic Heusler alloys with a strain of the order of 10% in an external magnetic field of less than one Tesla. In addition, the alloys exhibit a sequence of intermediate martensites with the modulated structures usually appearing at c/a < 1 while the low-temperature non- modulated tetragonal structures have c/a > 1. Typically, in the Ni-based alloys, the martensitic transformation is accompanied by a systematic change of the electronic structure in the vicinity of the Fermi energy, where a peak in the electronic density of states from the non-bonding Ni states is shifted from the occupied region to the unoccupied energy range, which is associated with a reconstruction of the Fermi surface, and, in most cases, by pronounced phonon anomalies. The latter appear in high-temperature cubic austenite, premartensite but also in the modulated phases. In addition, the modulated phases have highly mobile twin boundaries which can be rearranged by an external magnetic field due to the high magnetic anisotropy, which builds up in the martensitic phases and which is the origin of the magnetic shape memory effect. This overall scenario is confirmed by first-principles calculations.

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DETERMINATION OF CRYSTAL STRUCTURE AND CRYSTALLOGRAPHIC CHARACTERISTICS IN Ni-Mn-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS

International Journal of Modern Physics B ◽

10.1142/s0217979209061603 ◽

2009 ◽

Vol 23 (06n07) ◽

pp. 1771-1776

Author(s):

D. Y. CONG ◽

Y. D. ZHANG ◽

C. ESLING ◽

Y. D. WANG ◽

X. ZHAO ◽

...

Keyword(s):

Crystal Structure ◽

Shape Memory Alloys ◽

Shape Memory ◽

High Performance ◽

Room Temperature ◽

Martensitic Structure ◽

Magnetic Shape Memory ◽

Ferromagnetic Shape Memory Alloys ◽

Electron Backscattered Diffraction ◽

Ferromagnetic Shape Memory

Ni - Mn - Ga ferromagnetic shape memory alloys (FSMAs) have received great attention during the past decade due to their giant magnetic shape memory effect and fast dynamic response. The crystal structure and crystallographic features of two Ni - Mn - Ga alloys were precisely determined in this study. Neutron diffraction measurements show that Ni 48 Mn 30 Ga 22 has a Heusler austenitic structure at room temperature; its crystal structure changes into a seven-layered martensitic structure when cooled to 243K. Ni 53 Mn 25 Ga 22 has an I4/mmm martensitic structure at room temperature. Electron backscattered diffraction (EBSD) analyses reveal that there are only two martensitic variants with a misorientation of ~82° around <110> axis in each initial austenite grain in Ni 53 Mn 25 Ga 22. The investigation on crystal structure and crystallographic features will shed light on the development of high-performance FSMAs with optimal properties.

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Coexisting Multiple Martensites in Ni57−XMn21+XGa22 Ferromagnetic Shape Memory Alloys: Crystal Structure and Phase Transition

Metals ◽

10.3390/met11101534 ◽

2021 ◽

Vol 11 (10) ◽

pp. 1534

Author(s):

Lian Huang ◽

Daoyong Cong ◽

Mingguang Wang ◽

Yandong Wang

Keyword(s):

Magnetic Field ◽

Crystal Structure ◽

Phase Transition ◽

Shape Memory Alloys ◽

Shape Memory ◽

Alloy System ◽

Magnetic Shape Memory ◽

Ferromagnetic Shape Memory Alloys ◽

Ferromagnetic Shape Memory ◽

The Magnetic Field

A comprehensive study of the crystal structure and phase transition as a function of temperature and composition in Ni57−xMn21+xGa22 (x = 0, 2, 4, 5.5, 7, 8) (at. %) magnetic shape memory alloys was performed by a temperature-dependent synchrotron X-ray diffraction technique and transmission electron microscopy. A phase diagram of this Ni57−xMn21+xGa22 alloy system was constructed. The transition between coexisting multiple martensites with monoclinic and tetragonal structures during cooling was observed in the Ni51.5Mn26.5Ga22 (x = 5.5) alloy, and it was found that 5M + 7M multiple martensites coexist from 300 K to 160 K and that 5M + 7M + NM multiple martensites coexist between 150 K and 100 K. The magnetic-field-induced transformation from 7M martensite to NM martensite at 140 K where 5M + 7M + NM multiple martensites coexist before applying the magnetic field was observed by in situ neutron diffraction experiments. The present study is instructive for understanding the phase transition between coexisting multiple martensites under external fields and may shed light on the design of novel functional properties based on such phase transitions.

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Magnetic Shape Memory - Polymer Hybrids

Materials Science Forum ◽

10.4028/www.scientific.net/msf.879.133 ◽

2016 ◽

Vol 879 ◽

pp. 133-138 ◽

Cited By ~ 1

Author(s):

Ilkka Aaltio ◽

Frans Nilsén ◽

Joonas Lehtonen ◽

Yan Ling Ge ◽

Steven Spoljaric ◽

...

Keyword(s):

Magnetic Field ◽

Shape Memory ◽

Single Crystals ◽

Magnetic Particles ◽

Shape Change ◽

Shape Memory Polymer ◽

Raw Material ◽

Magnetic Shape Memory ◽

Polymer Hybrids ◽

The Magnetic Field

Martensitic Ni-Mn-Ga based alloys are known for the Magnetic Shape Memory (MSM) effect, which upon application of an external magnetic field can generate a strain up to 12 % depending on the microstructure of the martensite. The MSM effect occurs by rearrangement of the martensite variants, which is most advantageous in single crystals. Single crystals are, however, rather tedious to produce and there has been attempts to achieve MSM effect in polycrystals. However, in polycrystals the magnetic field induced shape change remains low as compared to single crystals. As an alternative to the former, hybrid MSM materials offer several advantages. When compared to single crystals, hybrids have extended freedom of shaping, lower raw material price, relatively large MSM strain and easier manufacturability. Embedding MSM particles into a suitable polymer matrix results in actuation function or good vibration damping performance. In the present study we report on the mechanical, structural and magnetic properties of MSM polymer hybrids, which are prepared by mixing gas-atomized Ni-Mn-Ga MSM powder into epoxy matrix and aligning the magnetic particles in a magnetic field.

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A first-principles study of the martensitic instabilities in magnetic shape memory alloys

MRS Proceedings ◽

10.1557/proc-1050-bb03-01 ◽

2007 ◽

Vol 1050 ◽

Cited By ~ 1

Author(s):

Peter Entel ◽

Markus Ernst Gruner ◽

Alfred Hucht

Keyword(s):

Magnetic Field ◽

External Magnetic Field ◽

Shape Memory ◽

First Principles ◽

Shape Change ◽

Heusler Alloys ◽

Phase Changes ◽

Magnetic Shape Memory ◽

Electronic Density ◽

Modulated Phases

AbstractAmong the magnetic shape memory Heusler alloys, Ni-Mn-Ga near stoichiometry displays the largest shape change in the martensitic 5M or 7M structure with a strain of the order of 10% in an external magnetic field of less than one Tesla. In addition, the alloys exhibit a sequence of intermediate martensites with the modulated structures usually appearing at c/a < 1 while the low-temperature nonmodulated tetragonal structures have c/a > 1. Typically, the martensitic phase changes are accompanied by a shift of a peak in the electronic density arising from the non-bonding Ni states, a reconstruction of the associated Fermi surface, and, in some cases, by pronounced phonon anomalies. These appear in the cubic high-temperature austenitic and premartensitic phases but also in the modulated phases. In addition, the modulated phases have highly mobile twins which can be rearranged under the action of an external magnetic field due to the high magnetic anisotropy, which builds up in martensite and which is at the origin of the magnetic shape memory effect. First-principles calculations confirm the overall scenario.

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Improvements to the Kiefer and Lagoudas Model for Prediction of the Magneto-Mechanical Behavior of Magnetic Shape Memory Alloys

ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Volume 1 ◽

10.1115/smasis2011-5066 ◽

2011 ◽

Author(s):

Alex Waldauer ◽

Heidi P. Feigenbaum ◽

Nickolaus M. Bruno ◽

Constantin Ciocanel

Keyword(s):

Magnetic Field ◽

Shape Memory Alloys ◽

Mechanical Behavior ◽

Shape Memory ◽

Inelastic Strain ◽

Magnetic Shape Memory ◽

Magnetic Shape Memory Alloys ◽

Demagnetizing Field ◽

Thermodynamic Basis ◽

Martensitic Variants

Magnetic shape memory alloys (MSMAs) are a class of materials that exhibit large, recoverable inelastic strain. After cooling from austenite to martensite, MSMAs have a tetragonal crystalline structure with three possible orientations called variants. These variants can rotate as a result of applied stress or applied magnetic field and the resulting inelastic strain can be as high as 10% [1]. To effectively use MSMAs in any potential application, a model that can accurately predict the magneto-mechanical behavior of the MSMA is required. Kiefer and Lagoudas developed a thermodynamic basis for modeling MSMAs and then apply it in the case where two of the three martensitic variants exist [2]. The improvements to the Kiefer and Lagoudas model proposed in this paper include a different analysis of the demagnetizing effect and an inclusion of the resulting axial demagnetizing field.

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Material Design, Processing, and Engineering Requirements for Magnetic Shape Memory Devices

10.18122/td/1739/boisestate ◽

2020 ◽

Author(s):

Andrew Armstrong

Keyword(s):

Magnetic Field ◽

Shape Memory ◽

Operating Temperature ◽

Shape Change ◽

Material Design ◽

Material Surface ◽

Magnetic Shape Memory ◽

Valence Electron Density ◽

Novel Technology ◽

Vertical Field

For magnetic shape memory (MSM) alloys, a magnetic field stimulates a shape change. We use the shape change to build devices such as micro-actuators, sensors, and microfluidic pumps. Currently, (as a novel technology,) devices suffer from some material and magnetic driver shortcomings. Here we address the issues related to operating temperature, repeatability, failure, and magnetic driver development. To increase the operating temperature of the MSM material, we alloyed Fe and Cu to Ni-Mn-Ga. We showed that the element-specific contribution to the valence electron density as parameter systematically determines the effect of each element on the variation of the martensite transformation temperature of the 10M phase. To stabilize the material, we developed a micro-shotpeening process that adds stresses to the material surface, thereby inducing a fine twin microstructure. The treatment allowed nearly full magnetic-field-induced strain, and extended fatigue life of the material from only one thousand cycles in the electropolished state to more than one million cycles in the peened state. We measured the effect of the peening process on material actuation when in MSM pump configuration. In the polished state, the deformation was stochastic, with a sharp-featured, faceted shrinkage. In the treated state, the deformation was smooth and repeatably swept along the surface akin to a wave. To actuate the MSM micropump without electromotor, we developed a linear electromagnetic actuation device and evaluated its effectiveness in the switching mechanism of the material. By compressing the magnetic field between opposing coils, we generated a strong magnetic field, which caused a localized region to switch at selected poles. In the next iteration of the drive, we inserted the MSM sample between two linear pole arrangements of high pitch density to approximate a moving vertical field. The incremental stepping of the vertical field between poles caused translation of the switched region. The results of this dissertation demonstrate the suitability of MSM alloys for high-precision, persistent, and reliable actuators such as micropumps.

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3D Energy Analysis of Magnetic-Field Induced Martensite Reorientation in Magnetic Shape Memory Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.738-739.400 ◽

2013 ◽

Vol 738-739 ◽

pp. 400-404 ◽

Cited By ~ 1

Author(s):

Yong Jun He ◽

Xue Chen ◽

Ziad Moumni

Keyword(s):

Magnetic Field ◽

Shape Memory Alloys ◽

Shape Memory ◽

Energy Analysis ◽

Three Dimensional ◽

Rotating Magnetic Field ◽

Magnetic Shape Memory ◽

Ferromagnetic Shape Memory Alloys ◽

Ferromagnetic Shape Memory ◽

Martensite Reorientation

This paper explains the magnetic-field induced martensite reorientation in Ferromagnetic Shape Memory Alloys (FSMA) through a simple energy analysis from which the role of the martensite’s magnetic anisotropy is emphasized. In particularly, with a three-dimensional (3D) energy analysis, we study the switching between the three tetragonal martensite variants driven by a rotating magnetic field (with a constant magnitude) and a non-rotating magnetic field (with a fixed direction but varying magnitudes). Finally, a simple planar phase diagram is proposed to describe the martensite reorientation in general 3D loadings.

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