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

Reinhold, Matthew; Kiener, Daniel; Knowlton, William B.; Dehm, Gerhard; Müllner, Peter

doi:10.1063/1.3211327

Cited by 21 publications

(15 citation statements)

References 45 publications

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“…At the largest applied bias stress of 11 MPa, the MFIS obtained with the small sized crystal was still close to 2%. To the authors knowledge, there is to date only one study reporting deformation experiments of Ni‐Mn‐Ga micropillars 111. While the very low force needed to trigger twinning of these 10 μm × 15 μm cross‐section pillars presented a challenge for detecting twinning events at the onset of the deformation experiments, twinning was found to occur at quite large stress levels (∼50 MPa) which may however be due to sample preparation.…”

Section: Structural Elements With One or More Small Dimensionsmentioning

confidence: 99%

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Size Effects on Magnetic Actuation in Ni‐Mn‐Ga Shape‐Memory Alloys

2010

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The off-stoichiometric Ni(2)MnGa Heusler alloy is a magnetic shape-memory alloy capable of reversible magnetic-field-induced strains (MFIS). These are generated by twin boundaries moving under the influence of an internal stress produced by a magnetic field through the magnetocrystalline anisotropy. While MFIS are very large (up to 10%) for monocrystalline Ni-Mn-Ga, they are near zero (<0.01%) in fine-grained polycrystals due to incompatibilities during twinning of neighboring grains and the resulting internal geometrical constraints. By growing the grains and/or shrinking the sample, the grain size becomes comparable to one or more characteristic sample sizes (film thickness, wire or strut diameter, ribbon width, particle diameter, etc), and the grains become surrounded by free space. This reduces the incompatibilities between neighboring grains and can favor twinning and thus increase the MFIS. This approach was validated recently with very large MFIS (0.2-8%) measured in Ni-Mn-Ga fibers and foams with bamboo grains with dimensions similar to the fiber or strut diameters and in thin plates where grain diameters are comparable to plate thickness. Here, we review processing, micro- and macrostructure, and magneto-mechanical properties of (i) Ni-Mn-Ga powders, fibers, ribbons and films with one or more small dimension, which are amenable to the growth of bamboo grains leading to large MFIS, and (ii) "constructs" from these structural elements (e.g., mats, laminates, textiles, foams and composites). Various strategies are proposed to accentuate this geometric effect which enables large MFIS in polycrystalline Ni-Mn-Ga by matching grain and sample sizes.

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Section: Structural Elements With One or More Small Dimensionsmentioning

confidence: 99%

“…Bottom left and right in (b) are a schematic of the twin pattern and a profile along the white line in the AFM image (top left in b). Reprinted with permission from 111. Copyright 2009, American Institute of Physics.…”

Section: Structural Elements With One or More Small Dimensionsmentioning

confidence: 99%

Size Effects on Magnetic Actuation in Ni‐Mn‐Ga Shape‐Memory Alloys

2010

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“…Many studies have described the twining effect and analyzed the relationship with grain morphology and size. For example, Reinhold et al 46 evaluated the twining in magnetic shape memory alloys (Ni-Mn-Ga) observing a preferential localization in planar and sharp ridges and valleys which are similar to the 47 reported the development of nanotwins in composites based on Ti and CNT observing similar twin effect as Ti-5% and 10% CNT substrates. Besides the potential improvements in hardness and strength due to twining, the presence of CNT it is expected to increase the mechanical strength of the blend because the CNT can reduce the stress concentration caused by the material porosity.…”

Section: Discussionmentioning

confidence: 78%

“…Many studies have described the twining effect and analyzed the relationship with grain morphology and size. For example, Reinhold et al evaluated the twining in magnetic shape memory alloys (Ni–Mn–Ga) observing a preferential localization in planar and sharp ridges and valleys which are similar to the morphology of Ti grain boundaries. In another study, Li et al reported the development of nanotwins in composites based on Ti and CNT observing similar twin effect as Ti‐5% and 10% CNT substrates.…”

Section: Discussionmentioning

confidence: 99%

Balancing biofunctional and biomechanical properties using porous titanium reinforced by carbon nanotubes

Pavón

López

Mondragón

et al. 2018

J Biomedical Materials Res

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Despite the well‐known advantages of the titanium‐based implant systems, they still lack an optimal balance between biofunctionality and mechanical strength, especially regarding the modulation of cellular response and a desired implant osseointegration. In this work, we fabricated a nanocomposite based on porous commercially pure grade 4 titanium (c.p. Ti) reinforced with carbon nanotubes (CNT) at 5% and 10% w/w, with the aim of obtaining a nanocomposite with lower stiffness compared to traditional titanium‐based implants and with the mechanical strength and bioactivity owed by the CNT. Results obtained by scanning electron microscopy, X‐ray photoelectron spectroscopy, and atomic force microscopy characterization showed that the CNT dispersed and incorporated into the porous c.p. Ti matrix. Interestingly, CNT were associated with a higher twining within neighbor Ti grains, which was indeed consistent with an increased in nano‐hardness. Biological evaluation by MTT and Comet assay revealed that the nanocomposites did not induce genotoxicity and cytotoxicity on two different cells lines despite the presence of nickel at the surface. Accordingly, a purification step would be required before these CNT can be used for biomedical applications. Our results indicate that incorporation of CNT into porous c.p. Ti is a promising avenue to achieve an adequate balance between biofunctionality and mechanical strength in Ti‐based scaffolds for tissue replacement. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 719–731, 2019.

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“…It was recently shown that the twin crystallography, the twin microstructure ͑including the morphology underneath the surface͒, and the magnetic domain structure of MSMA can be spatially resolved, nondestructively, with scanning probe microscopy. 15,16 The aim of the present work is to demonstrate the identification of twin crystallography and twinning history via the combined use of atomic force microscopy ͑AFM͒ and magnetic force microscopy ͑MFM͒ in situ as a function of temperature, thereby revealing the transformation path.…”

Section: Introductionmentioning

confidence: 99%

Transformation twinning of Ni–Mn–Ga characterized with temperature-controlled atomic force microscopy

Reinhold

Watson

Knowlton

et al. 2010

Journal of Applied Physics

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The magnetomechanical properties of ferromagnetic shape memory alloy Ni-Mn-Ga single crystals depend strongly on the twin microstructure, which can be modified through thermomagnetomechanical training. Atomic force microscopy ͑AFM͒ and magnetic force microscopy ͑MFM͒ were used to characterize the evolution of twin microstructures during thermomechanical training of a Ni-Mn-Ga single crystal. Experiments were performed in the martensite phase at 25°C and in the austenite phase at 55°C. Two distinct twinning surface reliefs were observed at room temperature. At elevated temperature ͑55°C͒, the surface relief of one twinning mode disappeared while the other relief remained unchanged. When cooled back to 25°C, the twin surface relief recovered. The relief persisting at elevated temperature specifies the positions of twin boundaries that were present when the sample was polished prior to surface characterization. AFM and MFM following thermomechanical treatment provide a nondestructive method to identify the crystallographic orientation of each twin and of each twin boundary plane. Temperature dependent AFM and MFM experiments reveal the twinning history thereby establishing the technique as a unique predictive tool for revealing the path of the martensitic and reverse transformations of magnetic shape memory alloys.

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

Cited by 21 publications

References 45 publications

Size Effects on Magnetic Actuation in Ni‐Mn‐Ga Shape‐Memory Alloys

Size Effects on Magnetic Actuation in Ni‐Mn‐Ga Shape‐Memory Alloys

Balancing biofunctional and biomechanical properties using porous titanium reinforced by carbon nanotubes

Transformation twinning of Ni–Mn–Ga characterized with temperature-controlled atomic force microscopy

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