Elsevier

Intermetallics

Volume 122, July 2020, 106799
Intermetallics

Giant high temperature superelasticity in Ni53Mn24Ga21Co1Cu1 microwires

https://doi.org/10.1016/j.intermet.2020.106799Get rights and content

Highlights

  • Phase transformation temperature increased significantly by the addition of Co and Cu.

  • Multiple phases coexist at as-prepared Ni-Mn-Ga-Co-Cu microwires.

  • Giant recoverable strain and superelasticity were obtained at elevated temperature range.

  • Shape memory microwires exhibit high cyclic stability at high temperature.

  • Proper heat treatment enhances the energy storage density.

Abstract

Ni-Mn-Ga is commonly used as a room temperature shape memory alloy. With the doping of Co and Cu, its phase transformation temperature increased to around 500 K, which can be used as high temperature shape memory alloys, and the superelasticity and shape memory strains are improved as well. Here, giant recoverable strain 16.3% is reported in a Heusler type Ni53Mn24Ga21Co1Cu1 microwire, prepared by rapid solidification via the Taylor-Ulitovsky method, with a diameter of 140 μm. Within a 150 K temperature range, the microwire maintains superelastic property of more than 10%. It has high cycle stability and the superelasticity remains almost unchanged after 100 cycles test at 523.15 K. It was also found that the energy loss density of the heat treated microwire is about twice than that of as-prepared microwire.

Introduction

Smart materials play an increasingly role in modern society. Ni-Mn-Ga shape memory alloys (SMAs) have drawn increasing attention in recent years due to their magnetic shape memory effect (MSME), damping capacities, magneto-caloric effect (MCE) and magnetic-torque-induced bending (MTIB), magnetic field-induced strain (MFIS), and such alloys can be potentially used as microactuators, magnetic cooling or energy harvesting devices [[1], [2], [3]]. Shape memory alloys exhibit superelasticity and shape memory properties because of a reversible phase transformation between austenite and martensite. Close to the transformation temperature, the high-symmetry parent phase can be deformed into low-symmetry martensite by external stress. Upon unloading, the martensite reversely transforms back to the parent phase. This stress-induced transformation is the origin of superelasticity. In bulk polycrystalline SMAs superelasticity is restrained by the brittle grain boundaries rarely exhibit large recoverable strain [4]. In order to overcome this problem, a change in the size of the sample may change its performance [5]. Li et al. [6] reported that mechanical and SME characteristics can be improved by grain refinement. Müllner [7] also proposed that reducing the sample size to small dimensions, such as in Ni–Mn–Ga powders, fibers, ribbons, foams [8], and microwires [[9], [10], [11]], can change the magneto mechanical properties and superelastic strain. Microwires improve mechanical properties by reducing grain binding, decreasing grain number in cross section and improving grain coordination. A Taylor-Ulitovsky method was proved to be a facile and effective way to reduce the geometrical constraints imposed by grain boundaries and the dimensions of the sample [[12], [13], [14]], bring in texture simultaneously, and consequently enhance the tensile superelasticity and ductility in SMAs. High temperature shape memory alloy refers to the shape memory alloy whose phase transformation temperature is higher than 473.15 K. Ni-Mn-Ga based shape memory alloys is usually applied at room temperature, high temperature is rarely used. With the doping of Co [15,16] and Cu [17] the transformation temperature transfer to a high temperature range as well as improve its mechanical properties, make it an alternative material for high temperature devices.

Section snippets

Experiments

In this paper, high purity Ni (99.97%) particles, Mn (99.97%) tablets, Ga (99.97%) blocks, Co (99.9%) plates, and Cu (99.98%) particles were selected as raw materials, the vacuum arc melting furnace is used for smelting. Because the melting points of various elements are quite different, the steps of first smelting NiMn intermediate alloy with 1:1 atomic ratio and then smelting Ni53Mn24Ga21Co1Cu1 alloy are adopted. For composition uniform the mass of the alloy ingot is around 45 g. The melting

Results and discussion

The phase transformation temperature of the Ni53Mn24Ga21Co1Cu1 alloy microwire was measured by DSC. The start and finish temperature of austenite transformation and martensite transformation, they are marked as As, Af, Ms, and Mf in Fig. 1 (a), which correspond to both the as-prepared and heat treated microwire, respectively. It can be clearly seen that after heat treatment, the phase transformation peaks become narrow and smooth, and shift to high temperature by nearly 30 K. Meanwhile, the Ni53

Conclusion

The properties of Ni53Mn24Ga21Co1Cu1 microwires prepared by the Taylor-Ulitovsky method, with the diameter of 140 μm, consisting of multi-martensite phase are mainly discussed. The as prepared microwire exhibits giant recoverable strain (~16.3%) and superelasticity (~14%) at 523.15 K, and maintains superelastic property of more than 10% with a large temperature range (150 K). It was also found that the energy loss density of the heat treated microwire is 0.071 J/g, which is about twice than

CRediT authorship contribution statement

Jianxing Zhang: Data curation, Writing - original draft. Zhiyi Ding: Data curation, Writing - review & editing. Ruihang Hou: Writing - review & editing. Jiajie Gao: Investigation. Jie Zhu: Supervision, Resources, Writing - review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work is supported by National High Technology Research and Development Program of China (863 Program) under Grant No. 2015AA034101 and the State Key Laboratory for Advanced Metals and Materials with Grant No. 2018Z-26.

References (18)

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