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Microstructure, mechanical properties as well as phase transformation behavior of newly developed Ni 49 Ti 36 Hf 15-x Ta (x=0, 3, 6, 9, 12) high temperature shape memory alloys has been investigated. Ni 49 Ti 36 Hf 15 alloy consists of (Ti,Hf) 2 Ni phase which is brittle and incoherent with the martensite matrix. However, addition of Ta in place of Hf suppresses the brittle (Ti,Hf) 2 Ni phase formation with white Ta rich phase. More than 70% reduction in area has been observed in Ta added Ni 49 Ti 36 Hf 15 high temperature shape memory alloys. The austenitic transformation temperature is well above 200 °C (473 K) for lower Ta concentrations with up to 6 at. %; however; at higher Ta concentrations (i.e. above 9 at. %) decreases significantly. Overall, the addition of Ta greatly influences the hot deformation behavior and high temperature shape memory properties of Ni 49 Ti 36 Hf 15 alloy. The present paper discusses the detailed investigation on Ni 49 Ti 36 Hf 15-x Ta (x=0, 3, 6, 9, 12) high temperature shape memory alloys.

Binary alloy nanowires of mutually immiscible Ni–Au system are synthesized by electrodeposition method. Here, we incorporate the concept of alloy design into nanowires to effectively engineer and control the magnetic properties of nanowires. Saturation magnetization and coercivity values of as-deposited Ni–Au alloy nanowires strongly correlate with either the phases present or to the dissolution of gold to nickel. The magnetic properties, however, were significantly affected upon annealing, which is correlated with the structural evolution of a weakly magnetic metastable hcp-Ni phase. We report here the detailed investigation on phase transformations in Ni–Au alloy nanowires and their effect on magnetic properties.

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.

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 Ni2MnGa at lower wheel speeds. However at higher wheel speeds nanocrystalline Ni2MnGa particles of size about 10-20 nm and martensitic phases were confirmed.

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, ? (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.

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 ? (gamma) phases. Amorphous phase, Ni2MnGa nanoparticles, and the martensite phase are analyzed in detail. � 2009 Springer Science+Business Media, LLC.