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Hysteresis related to first-order phase transformation in shape memory alloys, which is the macroscopic manifestation of energy dissipation, is detrimental to the precise control of actuation and causes structural and functional fatigue of components. It is of vital importance to explore high-performance shape memory alloys with low stress-hysteresis, large superelasticity, and wide temperature range operation in practical applications. Here, we have developed a Ni-Mn-Fe-In shape memory microwire, exhibiting an ultra-low stress-hysteresis and huge tensile superelasticity in a wide temperature range. The microwire shows a smooth surface and a single crystal structure (with ⟨001⟩A-oriented along the axial direction of microwire), and the microstructure of the microwire contains austenite matrix and sparsely distributed precipitates with an average size of 20–80 nm, all of which may be beneficial to obtain low hysteresis and large strains in the microwire. As a result, the microwire exhibits a minimum stress-hysteresis of as low as 8.5 MPa (with overall strain of 15.3%) and corresponding energy dissipation as low as 1.44 MJ/m3. The microwire always shows a low stress-hysteresis (less than 24 MPa) and low energy dissipation (less than 2.86 MJ/m3) above room temperature. The microwire shows a huge superelasticity with recoverable strains higher than 15% in the wide temperature range from 218 to 418 K. Together with the advantages of easy fabrication and no post-processing required, this microwire shows a tremendous potential for cyclic actuators and energy conversion devices under multi-field coupling. [ABSTRACT FROM AUTHOR]

The phase stability, martensitic transformation, and magnetic and mechanical properties of (Ni2-xCoxMn1.5Ti0.5)1-yBy (0 ≤ x ≤ 0.625; y = 0.03 and 0.06) alloys are systematically studied through the first-principles calculations method. The Co and B atoms are inclined to be aggregated distribution in the Ni2Mn1.5Ti0.5 alloy, and the phase stability of the austenite and non-modulated (NM) martensite decreases by co-doping. The ferromagnetic activation effect in the austenite occurs when x = 0.03 and y = 0.625. The magnetism of the austenite changes from an antiferromagnetic to a ferromagnetic state, which is ascribed to the elongation of the nearest neighboring distance of Mn–Mn, the nearest Mn–Mn distance increases from 2.50–2.79 to 2.90–2.94 Å, while the NM martensite always shows antiferromagnetism. Additionally, the doped B accelerates the change from antiferromagnetic to ferromagnetic for the austenite, but B-doping decreases the stability of the whole alloy system. The Co and B co-doping increases the stiffness of the NiMnTi alloy but decreases toughness and plasticity. However, the toughness and plasticity of the NiCoMnTiB alloy are better than those of the NiMnTiB alloy, indicating that the Co doping increases the d-orbital hybridization in the NiMnTiB alloy. The above results are expected to support the performance design of the NiMnTi-based alloy. [ABSTRACT FROM AUTHOR]

Reversibility of phase transformation, a basic requirement for functional properties of shape memory alloys, such as superelasticity, is severely affected by plastic deformation. Here, strain glass has been utilized to improve the reversibility of phase transformation. The incorporation of Al into Ti-Zr-Ni-Cu induces strain glass and endows the alloy with reversible phase transformation and thus ideal superelasticity. In situ x-ray diffraction and dynamic mechanical experiments were utilized to verify the mechanism for the conversion from transformation plasticity to superelasticity. This work provides a new way to improve the reversibility of phase transformation and expands the practical implications of strain glass. Conversion from transformation plasticity to reversible superelasticity is realized by employing the strain glass concept. [ABSTRACT FROM AUTHOR]

In this study, the influence of interstitial C atoms on the magnetostructural transformation and magnetocaloric effect in MnNi0.77Fe0.23GeCx (x = 0, 0.02, and 0.03) compounds has been investigated. The introduction of C atoms into the interstitial sites of the MnNi0.77Fe0.23Ge compounds leads to the enhanced stability of the orthorhombic phase, thus enhancing the structural transition temperature. Moreover, the critical field of antiferromagnetic (AFM)–ferromagnetic (FM) conversion significantly decreases following C atom incorporation. Therefore, it can be inferred that C atoms can promote the AFM–FM conversion in the TiNiSi-type orthorhombic phase. The MnNi0.77Fe0.23GeCx compound with x = 0.02 exhibits a large magnetocaloric effect due to the ferromagnetic magnetostructural transition. Furthermore, for the compound with x = 0.03, a table-like magnetocaloric effect is observed around room temperature owing to the coupling of the martensitic and metamagnetic transitions, which confirms the wide working temperature range and a large refrigerant capacity. [ABSTRACT FROM AUTHOR]

Oriented polycrystalline Nd1 − xTbxCo5 alloys are fabricated successfully by the magnetic field bonding technique, and magnetocrystalline anisotropy (MCA) and rotating magnetocaloric effect (RMCE) have been studied systematically. Two successive spin-reorientation transitions (SRTs), "easy-plane" to "easy-cone" transition at TSR1 followed by "easy-cone" to "easy-axis" transition at TSR2, are observed. The SRT temperatures shift toward room temperature due to the enhancement of MCA by substituting Nd with Tb of a higher MCA constant. In addition, two competing mechanisms on MCA might be induced by substituting Nd with Tb, which leads to the nonlinear variation of RMCE. The RMCE and the working temperature range increase largely by substituting Nd with a small amount of Tb, e.g., the maximum rotating adiabatic temperature change ΔTrot increases by ∼60% from x = 0 to 0.1. The relatively large RMCE over a wide working temperature range (from 240 K to 310 K) makes x = 0.1 compound attractive candidate for rotating magnetic refrigeration around room temperature. [ABSTRACT FROM AUTHOR]