Abstract
This study investigates the crystal structure, martensitic transformation behavior, magnetic properties, and magnetic-field-induced reverse martensitic transformation of Co64V15(Si21–xAlx) alloys. It was found that by increasing the Al composition, the microstructure changes from the martensite phase to the parent phase. The crystal structures of the martensite and parent phases were determined as D022 and L21, respectively. Thermoanalysis and thermomagnetization measurements were used to determine the martensitic transformation and Curie temperatures. Both the ferromagnetic state of the parent phase and that of the martensite phase were observed. With the increasing Al contents, the martensitic transformation temperatures decrease, whereas the Curie temperatures of both the martensite and parent phases increase. The spontaneous magnetization and its composition dependence were also determined. The magnetic-field-induced reverse martensitic transformation of a Co64V15Si7Al14 alloy under pulsed high magnetic fields was observed. Moreover, using the results of the DSC measurements and the pulsed high magnetization measurements, the temperature dependence of the transformation entropy change of the Co-V-Si-Al alloys was estimated.
Highlights
Shape memory alloys showing both shape memory effects and/or superelasticity are important functional materials, and many shape memory alloys have been reported, such as the NiTi [1], Cu-based [2], Fe-based [3], and Mg-based [4] alloy systems
Owing to the high phase stability of the Heusler phases, the martensitic transformation was not observed in the Co-based Heusler alloys except for Co2 NbSn, which does not exhibit half-metallic behavior [9]
This paper focuses on the CoV-based alloy system
Summary
Shape memory alloys showing both shape memory effects and/or superelasticity are important functional materials, and many shape memory alloys have been reported, such as the NiTi [1], Cu-based [2], Fe-based [3], and Mg-based [4] alloy systems. The forward martensitic transformation during cooling after heating to the parent phase cannot be detected owing to the diffusional transformation, and the sample degenerates only after one test of the shape memory effect for the as-quenched sample. To solve this problem, studies have been conducted by adding group III elements to lower the martensitic transformation temperature. By the application of a pulsed high magnetic field, the magnetic-field-induced reverse martensitic transformation was realized, which opens the possibility of its use as a multifunctional magnetic material for this new alloy system. Heusler alloys [15,20], was further investigate by using the results of differential scanning calorimeter (DSC) measurements and magnetization measurements in the pulsed fields
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