Pnina Ari-Gur - Academia.edu (original) (raw)

Papers by Pnina Ari-Gur

Materials

Ni–Mn-based Heusler alloys are known to demonstrate magnetic shape memory and giant magnetocalori... more Ni–Mn-based Heusler alloys are known to demonstrate magnetic shape memory and giant magnetocaloric effect (MCE). These effects depend on the phases, crystallographic and magnetic phase transitions, and the crystallographic texture characteristics. These structural characteristics, in turn, are a function of the processing parameters. In the current work, Ni55.5Mn18.8Ga24Si1.7 Heusler alloy was processed by melt-spinning under a helium atmosphere. This process results in a fine microstructure. The ribbon that was produced with a narrower nozzle width, faster wheel speed, and higher cast temperature, indicating a faster cooling rate, had double the magnetic entropy change close to room temperature. However, the other ribbon demonstrated a large entropy change over a broader temperature range, extending its usability. The effect of the melt-spinning process parameters on the developing microstructure, crystallographic structure and texture, transformation temperatures, and the magnetic...

International Journal of Materials Science and Applications, 2022

The scanning electron microscope (SEM) has evolved to become an indispensable tool for research a... more The scanning electron microscope (SEM) has evolved to become an indispensable tool for research and education in engineering, physics, nanotechnology, geosciences, materials science, biological sciences and other fields. However, training on a physical SEM is costly, time consuming, and often unavailable in economically disadvantaged areas. Advances in computer technology have made interactive three-dimensional (3D) virtual laboratory an effective tool for training in medicine and many engineering and technology fields. In the current work, in order to provide cost-effective hands-on training, a virtual 3D SEM was developed using the game development engine Unity 3D. It contains realistic 3D models of the physical components, created using 3ds Max ® , a software for 3D modeling and rendering. The components are manipulated with scripts programmed using C# and JavaScript and then paired with the corresponding model. Users may view and operate the virtual instrument, save images for further analysis, and write a report. The developed virtual SEM was tested on diverse groups of users at multiple institutions, each divided to treatment and control groups. Feedback from these tests was collected and used for improvements in the overall quality of the simulated experience. In addition, users reported the experience of training on the virtual SEM as enjoyable.

Canadian Metallurgical Quarterly, 1984

AbstractHot tearing during solidification occurs when grains separate along residual liquid at a ... more AbstractHot tearing during solidification occurs when grains separate along residual liquid at a grain boundary due to local strains. Separation can occur at temperatures below the solidus due to solute segregation, the minimum temperature being related to T DB, the ductile-brittle transition temperature. Measurements of T DB have been made in as-cast binary Pb alloys containing Sb, Bi, Sn, Na and Ca. The difference between T DB and the solidus temperature was found to be greatest for the PbSb alloys and least for the PbNa and PbCa alloys. Homogenization markedly changed T DB in the PbSb alloys indicating that both non-equilibrium and equilibrium solute segregation at the grain boundaries contributed to hot tearing. For a given maximum stress near T DB, the PbSn and PbCa alloys were much less susceptible to hot tearing than PbSb alloys. Resume Les felures a chaud au moment de la solidification se produisent lorsque, a cause des contraintes locales, les grains sont separes par un liquide residual que l'on ...

Nanomaterials, Apr 16, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

ABSTRACT Two tubes of 250 maraging steel, one forward shear-spun and the other backward-spun, wer... more ABSTRACT Two tubes of 250 maraging steel, one forward shear-spun and the other backward-spun, were studied both in the cold-worked state and after two different heat treatments: i) solution treatment followed by aging; ii) aging directly after cold working. X-ray measurements of preferred orientation and the calculation of the Crystallite urientation Distribution Function (CODF) were used as input for computation of Young's Modulus and the yield-stress anisotropy of the tubes. The predicted anisotropy of Young's Modulus in the tube wall was low but plastic properties were predicted to show higher anisotropy. After cold working, as well as after subsequent aging, higher uniaxial yield values are predicted for loading in the axial tube direction than in the tangential direction. Solution treatment between cold working and aging is predicted to change the yield behaviour, which is expected to become nearly isotropic. In all cases the through-thickness yield-stress is predicted to be lower than either the axial or the tangential yield-stress.

Materials Science and Engineering: B

Journal of Alloys and Compounds, 2022

Irradiation induced random displacements of atoms and replacement collision sequences are possibl... more Irradiation induced random displacements of atoms and replacement collision sequences are possible mechanisms for phase transformations as well as other physical properties changes as grain size variation and hardness increase or decrease. In this study Ni4Mo alloy samples were subject to low-flux bombardment by ion beams. This alloy has similar structure to the Hastelloy-C used in industry and to U3Si that is used as nuclear fuel. Sample regions were irradiated while the energy density of the bombarding beams was carefully controlled and the non-irradiated regions were kept close to room temperature. This way the irradiation induced temperature increase was highly localized creating ``quench-like'' conditions. After the irradiation, the samples were annealed at low temperature. Due to irradiation conditions there was a high density of nucleation sites favoring the formation of finer grain structures as well as localized phase transformations. The results showed that with th...

Materials Science and Engineering, 1980

The through-thickness distribution of texture and its relation to the distribution of plastic str... more The through-thickness distribution of texture and its relation to the distribution of plastic strain were studied in shear-spun steel tubes. The effects of heat treatment on the texture and on its distribution were also de termined. At the external tube surface the deformation approximated to a uniform elongation with a large superimposed tangential shear. A t the internal surface only the uniform elongation, analogous to ideal rolling conditions, was present. In the mid-thickness region extensive periodic shear parallel to the radial direction occurred, leading to a wavy flow-line pattern and extremely non-homogeneous textures. This local tilting of the pattern of metal flow drastically reduced the apparent texture in the mid-thickness region. Only solution treatment affected the texture, acting to reduce some components preferentially with respect to others. Aging treatments alone had no effect. The average texture, as determined from composite texture specimens, did not respond to solution heat treatment in the same way as the surface textures did. Changes in the processing parameters (in this case from forward to backward shear spinning) had a pronounced effect both on the pattern of metal flow and on the resultant textures.

Strength of Metals and Alloys, 1979

Philosophical Magazine Letters, Sep 2, 2016

We present our recent results on temperature behavior of magnetization observed in N i47M n39In14... more We present our recent results on temperature behavior of magnetization observed in N i47M n39In14 Heusler alloys. Three regions can be distinguished in the M −T diagram: (I) low temperature martensitic phase (with the Curie temperature TCM = 140K), (II) intermediate mixed phase (with the critical temperature TMS = 230K) exhibiting a reentrant like behavior (between TCM and TMS), and (III) high temperature austenitic phase (with the Curie temperature TCA = 320K) exhibiting a rather wide plateau region (between TMS and TCA). By arguing that powerful structural transformations, causing drastic modifications of the domain structure in alloys, would also trigger strong fluctuations of the order parameters throughout the entire M − T diagram, we were able to successfully fit all the data by incorporating Gaussian fluctuations (both above and below the above three critical temperatures) into the Ginzburg-Landau scenario.

Bimetallic composite nanotweezers based on Ti 2 NiCu alloy with shape memory effect (SME) have re... more Bimetallic composite nanotweezers based on Ti 2 NiCu alloy with shape memory effect (SME) have recently demonstrated the ability to manipulate real nano-objects, such as nanotubes, and bionanoparticles when heated to 40-60 °C by laser radiation. The possibility of developing nanotweezers operating at constant temperature is of particular importance mainly for the manipulation of biological objects. In this work, a microactuator was produced using a composite bilayer made of a layer of rapidly quenched Ni 53 Mn 24 Ga 23 ferromagnetic shape memory Heusler alloy and an elastic layer of Pt. The size of the microactuator is 25×2.3×1.7 µm 3 . A controlled bending deformation of the actuator of 1.2 %, with a deflection of the end of the actuator higher than 2 µm was obtained by applying a magnetic field of 8 T at T = 62 °C. The possibility of the development of new technologies for magnetic-field-controlled nanotools operating at a constant temperature using the new multifunction magnetic shape memory alloys will be discussed.

Social Science Research Network, 2022

Abstract: Abstract Entropy change of successive martensitic transformations in Ni-Mn-Ga... more Abstract: Abstract Entropy change of successive martensitic transformations in Ni-Mn-Ga Heusler alloys can be utilized to realize enhanced magnetocaloric properties. A detailed study of phase transformations of Ni2.15Mn0.85Ga, (ΔQ = 4900 J/kg at 343 K and 140 kOe) is reported here. Upon cooling, paramagnetic austenite (L21) transforms into a ferromagnetic 7M monoclinic martensitic phase. This phase is stable in a narrow temperature range and, upon further cooling, transforms into a non-modulated ferromagnetic tetragonal (L10) phase. The separation between the equilibrium temperatures of the L21 and the L10 phases is only ~50 K. The alloy undergoes reversible temperature-induced martensitic and inter-martensitic phase transformations with thermal hysteresis about 25 K. The conclusions from the detailed study of the phas...

Binary oxides of Mg and Ti were prepared by the sol-gel technique in various Mg/Ti atomic ratios,... more Binary oxides of Mg and Ti were prepared by the sol-gel technique in various Mg/Ti atomic ratios, r. Metastable phases, produced between 873 and 973 K from xerogels with Mg/Ti atomic ratios in the range ~1.1 < r ≤ 2, were studied by XRD and ND. XRD analysis showed crystal structures similar to that of Mg2TiO4 (qandilite), an inverse spinel of cubic structure. The composition range where this occurred did not correspond to those of the conventional equilibrium phase diagrams. The data were processed by the Rietveld method. ND data led to improvements in the refinement of the atomic occupancies. Assuming some degree of tetragonal distortion was effective only in ND analysis. It was found by ND that the charge balance is kept only for a certain extent of mixed occupancy of the octahedral sites, leading to a molecular formula Mg2-2xTi1+xO4, were 0 < x < 0.25. Using this formula as a constraint in the Rietveld refinement with XRD improved the Rietveld refinement. An important co...

Journal of Modern Processes in Manufacturing and Production, Aug 1, 2021

Journal of Metastable and Nanocrystalline Materials, 2005

IEEE Transactions on Magnetics, 2021

The entropy changes of successive martensitic phase transformations in Ni-Mn-Ga Heusler alloys ca... more The entropy changes of successive martensitic phase transformations in Ni-Mn-Ga Heusler alloys can be utilized to realize enhanced magnetocaloric properties. A detailed study of phase transformations of one such alloy, Ni2.15Mn0.85Ga, (ΔQ = 4900 J/kg at 343 K, under 140 kOe), is reported here. Upon cooling, the paramagnetic cubic (L21) austenitic phase transforms into a ferromagnetic 7M modulated monoclinic martensitic phase. This phase is stable in a narrow temperature range, and upon further cooling, transforms into a non-modulated ferromagnetic tetragonal (L10) phase. The separation between the equilibrium temperatures of the austenitic and tetragonal martensitic phases is only ~50 K. The alloy undergoes reversible temperature-induced martensitic and inter-martensitic phase transformations with thermal hysteresis of about 25 K. The conclusions from the detailed study of the phase transformations lead to new possibilities to enhance the magnetocaloric effect by utilizing the entropy associated with multi-structural transformations.

Smart Materials and Structures, 2016

Crystalline structure and magnetic behavior of the Ni 41 Mn 39 In 12 Co 8 alloy demonstrating gia... more Crystalline structure and magnetic behavior of the Ni 41 Mn 39 In 12 Co 8 alloy demonstrating giant magnetocaloric effect View the table of contents for this issue, or go to the journal homepage for more 2016 Smart Mater. Struct. 25 085013