Ni Mn Ga Particles Research Articles

Effect of Different Concentrations of NiMnGa Micro/Nanoparticles on the Kinetics of Natural Gas Hydration

To improve gas hydrate storage and transportation technology, ferromagnetic intermetallic compound NiMnGa particles with martensitic transformation endothermics were used to form micro/nanofluids with sodium dodecyl sulfate (SDS) to further strengthen the gas hydration process. In this work, the kinetic process of gas hydration in NiMnGa fluids with different concentrations (0, 0.1, 1, 2, and 3 wt.%) was investigated using a rotating magnetic field gas hydration separation experimental setup. The results show that the induction time of the 3 wt.% NiMnGa system was shortened by 98.3%, the gas consumption was increased by 50.5%, and the gas consumption rate was increased by 351.9% compared with the SDS system. Therefore, it is inferred from the mass transfer that NiMnGa micro/nanofluids can accelerate the formation of hydrates.

Microstructure, phase transformation and mechanical properties of NiMnGa particles/Cu composites fabricated by SPS

Microstructure, phase transformation and mechanical properties of NiMnGa particles/Cu composites prepared by spark plasma sintering method were investigated by SEM, EDS, XRD, susceptibility measurements and mechanical tests. The NiMnGa particles were found to react with Cu matrix and the composites exhibited a similar crystal structure to the Cu matrix. The martensitic transformation and Curie transition of the composites were weakened due to the composition change of NiMnGa particles caused by reactions. With increasing NiMnGa particles content, the martensitic transformation and Curie transition of the composites were enhanced to some extent. However, the martensitic transformation temperature and Curie transition temperature were decreased by ~50 K as compared to those of the original NiMnGa particles. The compressive strength of the composites increased with the increase of NiMnGa particles content, whereas the compressive strain was decreased gradually.

Investigation on porous NiMnGa alloy and its composite with epoxy resin

This article investigated microstructure, phase transformation and mechanical property of porous NiMnGa alloy and its composite with epoxy resin. The porous NiMnGa alloys with large pores and different porosity exhibited a similar martensitic transformation behavior but with reduced martensitic transformation temperature as compared to that of the original powder. The porous alloys exhibited low mechanical strength and ductility due to the existence of large size pores. After compositing with epoxy resin, the mechanical strength and ductility of the porous alloy had been apparently enhanced due to the synergistic effect between the polymer and porous alloy. In addition, the composite demonstrated a martensitic transformation behavior similar with that of the porous alloy, indicating that the constraint effect of polymer matrix on the phase transformation of the porous alloy could be neglected. The combination of porous NiMnGa alloys with continuous structure and polymer could provide a promising way to make NiMnGa/polymer composites with better performance than the composites consisting of NiMnGa particles and polymer.

Microstructure, phase transformation and mechanical property of porous NiMnGa alloys prepared by one-step sintering

This article investigated microstructure, martensitic transformation and mechanical property of porous NiMnGa alloys fabricated by one-step sintering method using Mg powder as a pore former. The overall pore size was decreased with decreasing Mg content due to the reduction of aggregation tendency of Mg particles. Residual Mg existed mainly in the pore wall (interfacial areas between NiMnGa and Mg) due to interfacial reactions. The porous alloys with different porosity exhibited one-step martensitic transformation with close transformation temperatures and the temperature of martensitic transformation was lower for the porous alloys than the original NiMnGa powder. The porous NiMnGa alloys exhibited a low compressive strength and ductility due to the existence of pores. The porous NiMnGa alloys with continuous pore wall structure could be a better candidate than NiMnGa particles to form composites with ductile matrix.

Effect of enhanced interfacial reaction on the microstructure, phase transformation and mechanical property of Ni–Mn–Ga particles/Mg composites

Abstract This study investigated the microstructure, phase transformation and mechanical property of Ni–Mn–Ga particles/Mg composites with a strong interfacial reaction between the particles and the matrix. The strong interfacial reaction was related to the large surface area and energy per unit volume of the flaky shape Ni–Mn–Ga particles that favors the reaction between the particles and matrix. The martensitic transformation behavior was largely weakened due to the interfacial reactions and thus the reduced volume fraction of Ni–Mn–Ga particles. The composites exhibited a much improved compressive strength and ductility in comparison with that of the Ni–Mn–Ga alloy. The compressive plasticity of the composites was decreased when the Ni–Mn–Ga particle content exceeded 40 wt%. In comparison with the Mg-composites with large size Ni–Mn–Ga particles, the composites with small size particles would have a much stronger interfacial reactions, which was detrimental to the phase transformation and mechanical ductility of the composites. The investigation results in this article could provide a reference for the design and preparation of the particles reinforced metal matrix functional composites.

Thermal and damping behaviour of magnetic shape memory alloy composites

Single crystals of ferromagnetic shape memory alloys (MSMA) exhibit magnetic field and stress induced strains via energy dissipating twinning. Embedding single crystalline MSMA particles into a polymer matrix could thus produce composites with enhanced energy dissipation, suitable for damping applications. Composites of ferromagnetic, martensitic or austenitic Ni–Mn–Ga powders embedded in a standard epoxy matrix were produced by casting. The martensitic powder composites showed a crystal structure dependent damping behaviour that was more dissipative than that of austenitic powder or Cu–Ni reference powder composites and than that of the pure matrix. The loss ratio also increased with increasing strain amplitude and decreasing frequency, respectively. Furthermore, Ni–Mn–Ga powder composites exhibited an increased damping behaviour at the martensite/austenite transformation temperature of the Ni–Mn–Ga particles in addition to that at the glass transition temperature of the epoxy matrix, creating possible synergetic effects.

Microstructure, phase transformation and mechanical property of Ni–Mn–Ga particles/Mg composites

This study investigated the microstructure, phase transformation and mechanical property of Ni–Mn–Ga particles/Mg composites. The Ni–Mn–Ga particles were well dispersed in the Mg matrix. The phase transformation temperatures of particles were not influenced by the matrix. Both compressive strength and ductility of the composites were improved by the particles.

Magnetic field induced strain and damping behavior of Ni–Mn–Ga particles/epoxy resin composite

This study investigated the magnetic field induced strain (MFIS) and damping behavior of the disordered and ordered Ni–Mn–Ga particles/epoxy composites. The apparent MFIS was detected in the ordered composite with 50wt% particle content. The composite exhibited a MFIS of ∼40ppm (strain-c) for expansion at martensite state which was much smaller than phase transformation strain (strain-c, ∼210ppm). The internal friction of the composites at glass transition temperature was enhanced with the addition of Ni–Mn–Ga particles, which might be attributed to the introduction of interfacial friction between particles and matrix. The ordered composite exhibited a lower damping ability than the disordered composite, which was attributed to the different distribution of particles in the two composites.

Compressive Fracture Behavior of Bi-added Ni50Mn28Ga22 Ferromagnetic Shape Memory Alloys

ABSTRACTIn order to develop NiMnGa/polymer composite materials, a production of single-crystal-like NiMnGa particles is important and should be developed for better quality. Although mechanical pulverization is a promising method by utilizing intrinsic intergranular brittleness of NiMnGa polycrystalline ingots, the amount of lattice defects introduced during mechanical crushing needs to be minimized. This must be achieved by enhancement of intergranular brittleness of NiMnGa particles. In this study, the effect of Bi addition on the compressive fracture behavior of polycrystalline Ni50Mn28Ga22 was investigated where Bi was expected to be segregated to the grain boundaries in NiMnGa, similar to Bi segregation to the grain boundaries in Ni. It was found that only intergranular fracture was observed in Ni50Mn28Ga22 polycrystals with 0.3 at.% Bi addition, although a mixture of intergranular and transgranular fracture was observed in Bi-free Ni50Mn28Ga22 polycrystal. Microalloying of Bi into NiMnGa enhances intergranular embrittlement. A number of spherical particles of Bi were confirmed on the fractured surface of Bi-doped NiMnGa polycrystals. The formation of Bi particles is a proof of the grain boundary segregation of Bi in NiMnGa.

Development of NiMnGa/Polymer Composite Materials

In this paper the recent development of NiMnGa-particles-embedded polymer-matrix magnetodriven composites achieved by our group is described. The NiMnGa single-crystal particles can be easily fabricated by mechanically crushing the polycrystalline ingots due to intrinsic intergranular brittleness. The elastic back stress from the matrix polymer induces the reverse reorientation of martensite variants after removing the magnetic field. However, the actuation strain observed was very small around 10ppm which was 1/1000 times lower than the calculated value. Some possible reasons for the disagreement are that the crystallographic orientation of NiMnGa particles is random distribution, lattice defects introduced during crushing suppress reorientation of martensite variants, and that the elastic restriction from the matrix polymer is higher than expected. Therefore, the martensite variant reorientation behavior of the NiMnGa/silicone composites has been investigated from the viewpoint of (1) volume fraction of matrix polymer, (2) elastic modulus of polymer and (3) direction of magnetic field applied. And also, the internal structures of the composites were directly evaluated by microfocused X-ray computed tomography (µ-CT).

Martensite Variant Reorientation of NiMnGa/Silicone Composites Containing Polystyrene Foam Particles

Effect of elastic modulus of matrix on ferromagnetic motion of NiMnGa particles was investigated for NiMnGa particles embedded silicone matrix composites with or without containing polystyrene form particles (PFPs), which are regarded as pores. NiMnGa single crystal was fabricated by a floating zone method and a cube-shape particle was fabricated with the surface orientation parallel to [100], [010] and [001] directions at the parent phase state. The elastic modulus of matrix polymer was controlled by changing the number of PFPs. It was found that the elastic modulus of silicone was decreased with increasing the volume fraction of PFPs. The magnetic-field-induced martensite variant reorientation (MVR) was evaluated by the magnetization curves obtained using a vibration sample magnetometer, and the magnetic field required for the start of martensite variant reorientation was reduced by increasing the number of PFPs. The control of elastic modulus of matrix polymer is important and a dominant factor for the magnetic motion of NiMnGa/polymer composites.

Phase transition of Ni–Mn–Ga alloy powders prepared by vibration ball milling

This study investigated the phase transformation of the flaky shaped Ni–Mn–Ga powder particles with thickness around 1 μm prepared by vibration ball milling and post-annealing. The SEM, XRD, DSC and ac magnetic susceptibility measurement techniques were used to characterize the Ni–Mn–Ga powders. The structural transition of Heusler → disordered fcc occurred in the powders prepared by vibration ball milling (high milling energy) for 4 h, which was different from the structural transition of Heusler → disordered fct of the powders fabricated by planetary ball milling (low milling energy) for 4 h. The two different structures after ball milling should be due to the larger lattice distortion occurred in the vibration ball milling process than in the planetary ball milling process. The structural transition of disordered fcc → disordered bcc took place at ∼320 °C during heating the as-milled Ni–Mn–Ga powders, which was attributed to the elimination of lattice distortion caused by ball milling. The activation energy for this transition was 209 ± 8 kJ/mol. The Ni–Mn–Ga powder annealed at 800 °C mainly contained Heusler austenite phase at room temperature and showed a low volume of martensitic transformation upon cooling. The inhibition of martensitic transformation might be attributed to the reduction of grain size in the annealed Ni–Mn–Ga particles.

Acoustic energy absorption in Ni–Mn–Ga/polymer composites

Composites of Ni–Mn–Ga particles in a polyurethane (PU) matrix are known to show up to 70% energy absorption under quasi-static mechanical loading. Reported here are results showing that the large mechanical energy absorption in Ni–Mn–Ga/PU composites persists up to at least 1 kHz and exceeds that in each of these control samples of pure PU, as well as in Fe 2(Tb 1/3Dy 2/3) particles in epoxy, and single crystal Ni–Mn–Ga. The transmitted acoustic amplitude decreases linearly with increase in frequency, consistent with the theory, and at 1 kHz it is 0.7 V in the Ni–Mn–Ga single crystal, 0.65 V in pure PU, 0.45 in the Fe 2(Tb 1/3Dy 2/3)/PU composites and 0.25 V in Ni–Mn–Ga/PU composites.

Internal stress dependent structural transition in ferromagnetic Ni–Mn–Ga nanoparticles prepared by ball milling

Ni–Mn–Ga nanoparticles were prepared by ball milling technique. X-ray diffraction pattern of the milled powders has a broad peak near the location of the prominent peak for the Heusler phase of Ni 2MnGa, indicating very disordered structures with small particle sizes. Structural properties of milled Ni–Mn–Ga particles recover to those of the bulk state after appropriate annealing temperature. It is worth noting that particles with size above 50 nm exhibit martensitic transformation. The average internal stress was calculated to be 2.83–1.13 MPa stored in the distorted lattice. Saturation magnetization of the milled sample increases with annealing temperature due to re-crystallization and grain growth.

The orientation dependence of transformation strain of Ni–Mn–Ga polycrystalline alloy and its composite with epoxy resin

This study investigated the transformation strains of Ni–Mn–Ga polycrystalline alloy and Ni–Mn–Ga/epoxy resin composites. For the Ni–Mn–Ga polycrystalline alloy, the columnar grains formed along the solidification direction, and the alloy expanded during martensitic transformation in the direction with a transformation strain of ∼500 ppm. For the composite consisting of randomly distributed Ni–Mn–Ga particles, no transformation strain was achieved due to the random distribution of the Ni–Mn–Ga particles. For the composite consisting of properly oriented Ni–Mn–Ga particles, the martensitic transformation strains were found to be orientation-dependent, the shrinking transformation strain-c (parallel to the direction of magnetic field used during curing) up to ∼210 ppm was detected, and the expanding transformation strain-a (vertical to the direction of magnetic field used during curing) was measured to be ∼150 ppm.

Bending properties of epoxy resin matrix composites filled with Ni–Mn–Ga ferromagnetic shape memory alloy powders

Two types of epoxy resin matrix composites filled with Ni–Mn–Ga ferromagnetic shape memory alloy powders, with and without magnetic field during curing, were prepared, aiming to create anisotropic and isotropic alignments of the Ni–Mn–Ga particles. The bending properties of the composites are found to be significantly influenced by the distribution of Ni–Mn–Ga particles in the epoxy matrix. The composites without magnetic field during curing exhibit larger bending strength and fracture strain than the composites with magnetic field during curing. The fractography reveals that the Ni–Mn–Ga particle chains formed in the composites with magnetic field during curing facilitate the initiation and propagation of cracks, thus weakening the bending properties.

Stress-Induced Twin Boundary Motion in Particulate Ni-Mn-Ga /Polymer Composites

Composites of Ni–Mn–Ga particles in a polyurethane matrix can be made by mixing the particles with the polymer, and allowing them to cure under a magnetic field to texture the composites. These composites show large hysteresis and mechanical losses, when subjected to a cyclic stress, that were far larger than the matrix polymer ones. The additional losses are attributed to the motion of twin boundaries in the filler particles and provide a way for obtaining mechanical energy absorption in a wide frequency range. By means of X-ray and neutron diffraction we present evidence that confirms that twins are present in the particles and that they do move when mechanically loading the composite

Damping Characteristics of a NiMnGa/Polymer Composite Material

NiMnGa alloys are attractive for the magnetic induced shape memory effect, especially as promising functional elements in smart composite materials and structures. Recently, more attentions are put on NiMnGa composite materials. In this paper, NiMnGa particles have been dispersed and oriented in a polymer matrix with high content under magnetic field. The damping behavior of NiMnGa/polymer composites was investigated in by DMA, contrasting to the pure polymer.

Electron microscopy investigation of spark-eroded Ni–Mn–Ga ferromagnetic shape-memory alloy particles

The microstructural and chemical characteristics of Ni–Mn–Ga particles produced by spark-erosion using liquid argon or liquid nitrogen dielectrics were investigated by electron microscopy techniques. The particles were predominantly micron-sized spheres; those obtained in argon were solid, whereas those obtained in nitrogen were primarily hollow. The investigation of annealed particles revealed twinned microstructure and provided evidence supporting the cryogen solubility model of hollow particle formation, as well as possibly explaining the non-homogeneous structure of particles formed by spark-erosion in liquid nitrogen.

Polyester-bonded textured composites with single-crystalline shape memory Ni–Mn–Ga particles

Single-crystalline Ni 51Mn 27Ga 22 particles with the five-layered martensite structure (5M) were prepared by mortar grinding of annealed melt-extracted fibres. These particles were embedded in a stiffness-matched polyester matrix and textured by an alignment field. With increasing compression stress, the magnetic properties of the composites could be continuously changed. Magnetisation measurements of compressed composites, indirectly indicate stress-induced twin boundary motion in the MSM particles.