This study reports detailed microstructural and magnetic characterization of rapidly solidified Ni2(Mn,Fe)Ga heusler alloys processed using the melt spinning technique. Series of Ni50Mn(25-x)Fe( x= 2, 5, 8, 11)Ga25 alloys were prepared by vacuum arc melting and then melt spun at constant wheel speed of 20 m/sec to obtain samples in the form of ribbons. X-ray diffraction analysis of as-cast Ni 2(Mn,Fe)Ga alloy with different 'Fe' concentrations revealed austenite phase with L21 Heusler atomic order at room temperature. Transmission electron microscopy of melt spun ribbons reveals a precursor tweed structures due to magnetic tweed contrast when the 'Fe' concentrations are 8% and 11%. In case of 11% 'Fe' substituted alloy martensite phase was found to from at the grain boundary triple junctions. Thermo magnetic measurements determine that, as the 'Fe' concentration increases from 2 to 11%; it enhances the magnetic transition temperature from 375 to 403 K. © (2009) Trans Tech Publications.

Phanikumar Gandham

Department of Metallurgical and Materials Engineering

R.V.S. Prasad

M. Manivel Raja

As-cast

ATOMIC ORDERS

Austenite phase

GRAIN BOUNDARY TRIPLE JUNCTIONS

Heusler

Heusler alloy

Heusler alloys

Magnetic characterization

Magnetic measurements

Magnetic transition temperature

Martensite phase

Melt-spinning techniques

Melt-spun

Melt-spun ribbons

Micro-structural

Rapidly solidified

Room temperature

Vacuum arc melting

WHEEL SPEED

Cerium alloys

Gallium

Gallium alloys

Grain boundaries

Magnetic properties

Magnetism

Manganese

Manganese compounds

Martensite

Melt spinning

Rapid Solidification

Ternary systems

Transmission electron microscopy

Vacuum applications

X ray diffraction analysis

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

Advanced Materials Research

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

In this study microstructure and magnetic properties of cobalt substituted Ni 2MnGa based ferromagnetic shape memory alloys (FMSA) are presented. Ni 50Mn (25-x)Co xGa 25 (x = 2, 5, 8, 11 at%) alloys were synthesized using the melt-spinning technique. Martensite, austenite and pre-martensitic tweed structures were found at room temperature for alloys containing 2, 5, 8 and 11% Co and melt-spun at two extreme wheels speeds viz., 20 m/s and 30 m/s. However, the alloy containing 5% Co melt-spun at a wheel speed of 20 m/s consists of 7 M or 14 layered Martensite phase. Magnetic properties such as saturation magnetization (Ms), martensitic transformation temperature (T m) and Curie temperature (T c) were measured and were found to be attractive for most of the melt-spun alloys containing higher "Co" concentrations. Upon annealing at 1273 K for 1 h, γ (gamma) phase was found to stabilize. The magnetic properties were found to correlate with the phase content of the Co substituted alloys. © 2012 Elsevier Ltd. All rights reserved.

Intermetallics

Structure and magnetic properties of Ni 2(Mn,Co)Ga Heusler alloys rapidly solidified by melt-spinning

Microstructure and magnetic properties of rapidly solidified Ni 2(Mn,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.

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

Development of CMOS-MEMS/NEMS Devices

Synfacts

Synthesis of Pyrrole-Based HMG-CoA Reductase Inhibitors

Journal	Advanced Materials Research
ISSN	10226680
Open Access	No