Reversible Martensitic Transformation under Low Magnetic Fields in Magnetic Shape Memory Alloys

Magnetic field-induced, reversible martensitic transformations in NiCoMnIn meta-magnetic shape memory alloys were studied under constant and varying mechanical loads to understand the role of coupled magneto-mechanical loading on the transformation characteristics and the magnetic field levels required for reversible phase transformations. The samples with two distinct microstructures were tested along the [001] austenite crystallographic direction using a custom designed magneto-thermo-mechanical characterization device while carefully controlling their thermodynamic states through isothermal constant stress and stress-varying magnetic field ramping. Measurements revealed that these meta-magnetic shape memory alloys were capable of generating entropy changes of 14 J kg(−1) K(−1) or 22 J kg (−1) K(−1), and corresponding magnetocaloric cooling with reversible shape changes as high as 5.6% under only 1.3 T, or 3 T applied magnetic fields, respectively. Thus, we demonstrate that this alloy is suitable as an active component in near room temperature devices, such as magnetocaloric regenerators, and that the field levels generated by permanent magnets can be sufficient to completely transform the alloy between its martensitic and austenitic states if the loading sequence developed, herein, is employed

Compressive Response of Polycrystalline NiCoMnGa High-Temperature Meta-magnetic Shape Memory Alloys

The effects of the addition of quaternary element, Co, to polycrystalline NiMnGa alloys on their magnetic and shape memory properties have been investigated. NiCoMnGa polycrystalline alloys have been found to demonstrate good shape memory and superelasticity behavior under compression at temperatures greater than 100 °C with about 3% transformation strain and low-temperature hysteresis. It is also possible to train the material to demonstrate a large two-way shape memory effect

In situ, 3D characterization of the deformation mechanics of a superelastic NiTi shape memory alloy single crystal under multiscale constraint

Microstructural elements in NiTi shape memory alloys (SMAs) e precipitates, phase boundaries, inclusions

Glassy phonon heralds a strain glass state in a shape memory alloy

Shape memory strain glasses are frustrated ferroelastic materials with glasslike slow relaxation an

Compressive response of Ni45.3Ti34.7Hf15Pd5 and Ni45.3Ti29.7Hf20Pd5 shape-memory alloys

The shape-memory properties of Ni45.3Ti34.7Hf15Pd5 and Ni45.3Ti29.7Hf20Pd5 polycrystalline alloys were determined through superelasticity and shape-memory tests in compression. It has been revealed that the Ni45.3Ti34.7Hf15Pd5 has a maximum transformation strain of 3.8 % and work output of up to 30 J cm(-3), while the Ni45.3Ti29.7Hf20Pd5 has a maximum transformation strain of 2.6 % and work output of up to 20 J cm(-3) at 700 MPa. Two-way shape-memory strains of 0.6 and 0.85 % were obtained in Ni45.3Ti34.7Hf15Pd5 and Ni45.3Ti29.7Hf20Pd5 alloys, respectively. The Ni45.3Ti34.7Hf15Pd5 showed superelasticity at 90 A degrees C with recoverable strain of 3.1 %, while high hardening of Ni45.3Ti29.7Hf20Pd5 limited its superelastic behavior. Microstructure of the Ni45.3Ti34.7Hf15Pd5 alloy was revealed by transmission electron microscopy, and effects of composition on the lattice parameters of the transforming phases and martensite morphology were discussed

Characterization of the shape memory properties of a Ni45.3Ti39.7Hf10Pd5 alloy

The load-biased shape memory and superelastic responses of a Ni45.3Ti39.7Hf10Pd5 polycrystalline alloy were investigated in compression. Transformation strain of up to 4.6% and work output of up to 29 J cm(-3) were determined from load-biased thermal cycling experiments. The alloy showed good superelastic behavior at 90 degrees C with recoverable strain of over 4%. It was also determined that the Ni45.3Ti39.7Hf10Pd5 alloy could develop two-way shape memory strain of 1.6% without an intense training process. Transmission electron microscopy (TEM) revealed that the internal twins formed in the martensite variants were type II twins. (c) 2013 Elsevier B.V. All rights reserved

Orientation dependence of the shape memory properties in aged Ni45.3Ti29.7Hf20Pd5 single crystals

The shape memory properties of Ni45.3Ti29.7Hf20Pd5 single crystals aged at 550 degrees C for 3 h and at 600 degrees C for 48 h were investigated along the [111], [011] and [ 117] orientations in compression. The material was stronger along the [-117] orientation compared to the [111] and [011] orientations based on load-biased thermal cycling experiments. The shape memory properties such as reversible strain, temperature hysteresis, critical stress for stress-induced martensite transformation and Clausius-Clapeyron relations were also strong functions of orientation and aging condition (precipitate characteristics). Shape memory effect with no or negligible irrecoverable strain was observed under stress levels as high as 1000 MPa. After aging at 550 degrees C for 3 h, the maximum reversible strains were 2.2%, 2.7% and 0.7% along the [111], [011] and [ 117] orientations, respectively. Aging at 600 degrees C for 48 h resulted in maximum reversible strains of 2.3%, 3.2% and 0.9% along the [111], [011] and [-117] orientations, respectively. In both cases, similar levels of transformation strain, as a function of orientation, were observed during superelastic testing. The maximum work output reached 27 J/cm(3) in the [011] orientation after aging at 550 degrees C for 3 h. (C) 2014 Elsevier Ltd. All rights reserved