Abstract
Meta-magnetic shape-memory alloys combine ferroelastic order with ferromagnetic order and exhibit attractive multifunctional properties, but they are extremely brittle, showing hardly any tensile deformability, which impedes their practical application. Here, for the first time, an Ni-Cu-Co-Mn-In microwire has been developed that simultaneously exhibits a magnetic field-induced first-order meta-magnetic phase transition and huge tensile superelasticity. A temperature-dependent in situ synchrotron high-energy X-ray diffraction investigation reveals that the martensite of this Ni43.7Cu1.5Co5.1Mn36.7In13 microwire shows a monoclinic six-layered modulated structure and the austenite shows a cubic structure. This microwire exhibits an oligocrystalline structure with bamboo grains, which remarkably reduces the strain incompatibility during deformation and martensitic transformation. As a result, huge tensile superelasticity with a recoverable strain of 13% is achieved in the microwire. This huge tensile superelasticity is in agreement with our theoretical calculations based on the crystal structure and lattice correspondence of austenite and martensite and the crystallographic orientation of the grains. Owing to the large magnetization difference between austenite and martensite, a pronounced magnetic field-induced magnetostructural transition is achieved in the microwire, which could give rise to a variety of magnetically driven functional properties. For example, a large magnetocaloric effect with an isothermal entropy change of 12.7 J kg-1 K-1 (under 5 T) is obtained. The realization of magnetic-field- and tensile-stress-induced structural transformations in the microwire may pave the way for exploiting the multifunctional properties under the coupling of magnetic field and stress for applications in miniature multifunctional devices.
Highlights
High-performance intelligent materials are important for the intelligent systems that are greatly required in our modern society
A temperature-dependent in situ synchrotron high-energy X-ray diffraction investigation reveals that the martensite of this Ni43.7Cu1.5Co5.1Mn36.7In13 microwire shows a monoclinic sixlayered modulated (6M) structure and the austenite shows a cubic structure
This microwire exhibits an oligocrystalline structure with bamboo grains, which remarkably reduces the deformation and transformation strain incompatibility, allowing the deformation and martensitic transformation to occur in a much less constrained environment
Summary
High-performance intelligent materials are important for the intelligent systems that are greatly required in our modern society. Producing an oligocrystalline structure in which the surface area is larger than the total grain boundary area and the triple junctions are reduced or even eliminated could diminish the incompatibility between different grains, allowing the deformation and martensitic transformation in SMAs to occur in a much less constrained environment (Ueland et al, 2012) This could effectively inhibit brittle intergranular fracture and enhance the mechanical properties (Chen et al, 2009). We have successfully developed an oligocrystalline Ni–Cu–Co–Mn–In microwire exhibiting both a pronounced magnetic field-induced magnetostructural transition and huge tensile superelasticity with a recoverable strain of 13% In this microwire, a small amount of Cu is added to improve the ductility, and the formation of an oligocrystalline structure effectively suppresses brittle intergranular fracture. The present microwire, showing both a reversible magnetic field-induced magnetostructural transition and tensile superelasticity, has enormous potential for applications in miniature multifunctional devices
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