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.

Phanikumar Gandham

Department of Metallurgical and Materials Engineering

R. V. S. Prasad

M. Srinivas

M. Manivel Raja

Austenite

Curie temperature

Gallium

Gallium alloys

Magnetic properties

Manganese

Martensitic transformations

Melt spinning

microstructure

Nickel

Rapid Solidification

Saturation magnetization

Wheels

ATOMIC ORDERING

Austenite phase

Martensitic transformation temperatures

Processing condition

Processing technique

Rapidly solidified

Room temperature

Temperature increase

Iron alloys

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

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

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

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.

Materials Characterization

Premartensite transition in Ni2FeGa Heusler alloy

Compositional instability and phase formation in Ni-Fe-Ga Heusler alloys are investigated. The alloys are synthesized into two-phase microstructure. Their structures are identified as fcc and L<inf>21</inf>, respectively. The γ-phase formation could be suppressed with higher Ga-content in the alloy as Ga stabilizes austenite phase, but Ga lowers the martensite transformation temperature. The increase of Fe content improves the magnetization value and the increase of Ni from 52 to 55 at. pct raises the martensite transformation temperature from 216 K to 357 K (−57 °C to 84 °C). Magnetic properties and martensitic transformation behavior in Ni-Fe-Ga Heusler alloys follow opposite trends, while Ni replaces either Fe or Ga, whereas they follow similar trends, while Fe replaces Ga. Modulated martensite structure has low twinning stress and high magneto crystalline anisotropic properties. Thus, the observation of 10- and 14 M-modulated martensite structures in the studied Ni-Fe-Ga Heusler alloys is beneficial for shape memory applications. The interdependency of alloy composition, phase formation, magnetic properties, and martensite transformation are discussed. © 2015, The Minerals, Metals & Materials Society and ASM International.

Martensite Transformation and Magnetic Properties of Ni-Fe-Ga Heusler Alloys

Microstructure of rapidly solidified Ni2MnGa ferromagnetic shape memory alloy has been investigated experimentally by melt-spinning technique. At a constant ribbon width of 3 mm, two speeds of melt spinning 17m/sec and 30m/sec at the extrema of conditions for a good quality of ribbon resulted in two thicknesses of the ribbon, viz., 62 μm and 44 μm, respectively. TEM and AFM analysis reveals the formation of very fine clusters of Ni 2MnGa at lower wheel speeds. However at higher wheel speeds nanocrystalline Ni2MnGa particles of size about 10-20 nm and martensitic phases were confirmed. © (2010) Trans Tech Publications.

Materials Science Forum

Martensite and nanocrystalline phase formation in rapidly solidified Ni2MnGa alloy by melt-spinning

Melt spinning technique was used to synthesize Ni2MnGa ferromagnetic shape memory alloy ribbons. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis of the ribbon synthesized at lower wheel speed (20 m/s) reveal the formation of very fine clusters of austenitic phase of Ni2MnGa. However at higher wheel speed (30 m/s) the formation of martensite and nanoparticles of Ni2MnGa with a size range of 10-20 nm in the amorphous matrix is observed. Also an amorphous phase was observed at higher wheel speed in some areas of the ribbon. Annealing (1000 °C, 1 h) of the ribbon synthesized at higher wheel speed resulted in martensite and γ (gamma) phases. Amorphous phase, Ni2MnGa nanoparticles, and the martensite phase are analyzed in detail. © 2009 Springer Science+Business Media, LLC.

Journal of Materials Science

Amorphous and nano crystalline phase formation in Ni2MnGa ferromagnetic shape memory alloy synthesized by melt spinning

Magneto-microstructural coupling during stress-induced phase transformation in Co49Ni21Ga30 ferromagnetic shape memory alloy single crystals

Phenomenological description of thermomechanical behavior of shape memory alloy

Ab initio investigation of twin boundary motion in the magnetic shape memory Heusler alloy Ni2MnGa

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

Journal	Data powered by TypesetMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Publisher	Data powered by TypesetSpringer Boston
ISSN	10735623
Open Access	No