Martensitic phase transformation of Ni2FeGa Heusler alloy was studied by differential scanning calorimetry. Atomic ordering induced in the austenite structure by quenching from high temperature plays a significant role on martensitic phase transformation. Higher magnetization and larger magneto-crystalline anisotropy of martensite phase than that of austenite phase are noticed. Tweed contrast regions observed in the transmission electron microscopy were correlated to premartensite phenomena. A shift in premartensitic transition temperature prior to martensitic transformation as measured by differential scanning calorimetry is being reported for the first time in this system. © 2015 Elsevier Inc. All rights reserved.

Phanikumar Gandham

Department of Metallurgical and Materials Engineering

Hrusikesh Nath

Austenite

Calorimeters

Calorimetry

Differential scanning calorimetry

Magnetization

Martensite

Nickel

Phase Transitions

Transmission electron microscopy

ATOMIC ORDERING

Austenite phase

Heusler alloys

High temperature

Martensite phase

MARTENSITE TRANSFORMATIONS

MARTENSITIC PHASE TRANSFORMATIONS

TWEED CONTRAST

Martensitic transformations

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

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IIT Madras

Materials Characterization

Ni2FeGa polycrystalline alloys are synthesized by arc melting into single phase β structure and two phase mixture of γ-phase (fcc) and austenite (L21). Annealing improves atomic ordering and β transforms to L21 ordered structure. Effect of alloy composition and processing condition on different phase formation, microstructural, magnetic and electrical properties are discussed. The alloy undergoes first order austenite to martensitic phase transformation at 225&nbsp;K with low hysteresis of 10&nbsp;K. The resistivity exhibits a jump upon martensite transformation. This increase in resistivity is being attributed to the change in effective mass of electron upon martensite transformation. The temperature dependent resistivity curve for both austenite and martensite varies linearly with αT suggesting strong electron–phonon scattering. The slope of temperature dependent resistivity curve is higher in case of austenite than that of martensite and is attributed to the increasing role of electron–phonon scattering at high temperature. © 2015, The Indian Institute of Metals - IIM.

Transactions of the Indian Institute of Metals

Microstructural, Magnetic and Electrical Properties of Ni2FeGa Heusler Alloys

The microstructure and magnetic properties of Ni2MnGa base alloys with "Fe" substitution in place of "Mn" are studied. The processing technique used is melt spinning at wheel speeds of 20 m/s and 30 m/s followed by annealing at 1273 K (1000 °C) for 1 hour. Fe content is varied from 2 at. pct to 11 at. pct for alloys of Ni50Mn (25-x)Fe x Ga25 with Heusler stoichiometry. Austenite with B2 partial atomic ordering and premartensitic tweed structures were found at room temperature for all the alloys at different wheel speeds. After annealing at 1273 K (1000 °C) for 1 hour, austenite phase with L2 1 Heusler atomic ordering is stabilized in samples of all the processing conditions. Saturation magnetization, martensitic transformation temperature, and Curie temperature are measured. Martensite temperature and Curie temperature increase in proportion to iron content in the alloy. Saturation magnetization is sensitive to the phase content and compositional inhomogeneities. © 2013 The Minerals, Metals &amp; Materials Society and ASM International.

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Microstructure and magnetic properties of Ni2(Mn,Fe)Ga heusler alloys rapidly solidified by melt spinning

The Ni2FeGa Heusler alloy is synthesized by arc melting in argon atmosphere. It shows two phase microstructure, γ-phase (disordered fcc) and Austenite (ordered bcc, L21). Phase identification and microstructural characterization were carried out using XRD, SEM and TEM. Solidification at various undercoolings upto 215 °C was performed using flux undercooling technique. B2O3 was used as the flux that provides an inert atmosphere and isolates the molten pool from the quartz tube. The solidified microstructure of the undercooled samples were analyzed and the result indicates γ-phase to be the primary phase to form. The samples are also textured. XRD patterns indicate different texture at different undercoolings. Possible mechanisms for such changes will be discussed. The competitive nucleation mechanism can not also be ruled out as the SEM micrographs show the globular morphology of γ-phase likely due to defragmentation of primary dendrites. Thermal analysis by DSC shows incongruent melting of Ni2FeGa Heusler alloy which strengthen the argument of poor nucleation ability of L21 ordered intermetallic austenite phase as compared to primary γ-phase. Up to achieved undercooling limits, γ-phase forms as the primary phase competitively with the L21 ordered phase. Studies indicate that competitive nucleation mechanism is a likely mechanism to explain the phase selection. © (2014) Trans Tech Publications, Switzerland.

Materials Science Forum

Microstructure and phase evolution of Ni2FeGa heusler alloy extended to different degrees of undercooling

Microstructure and properties of bulk samples of Ni50Co 23Fe2Ga25 Heusler alloy undercooled and solidified in an electromagnetic levitation facility have been studied. Microstructure characterization showed the samples to consist of a mixture of fcc phase and non-modulated tetragonal martensite phase at low undercoolings and a single phase microstructure containing only martensite at high undercooling. The fcc phase content increases with undercooling up to 170 K and then disappears at undercooling above 200 K. Hardness and magnetization correlate differently with the phase content of the sample. © 2011 Elsevier Ltd. All rights reserved.

Intermetallics

Phase evolution and properties of Ni50Co23Fe 2Ga25 Heusler alloy undercooled by electromagnetic levitation

physica status solidi (a)

Enhancement of the martensitic transformation and magnetocaloric effect of Ni-Mn-V-Sn ribbons by annealing treatment

Hot deformation behavior of Ni–Fe–Ga-based ferromagnetic shape memory alloy – A study using processing map

Premartensite transition in Ni2FeGa Heusler alloy

Journal	Data powered by TypesetMaterials Characterization
Publisher	Data powered by TypesetElsevier Inc.
ISSN	10445803
Open Access	No