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Xin Y.,North China Electrical Power University | Chai L.,Beijing Key Laboratory for Advanced Functional Materials and Thin Film Technology
Rare Metals | Year: 2014

Microstructure, martensitic transformation behavior, mechanical and shape memory properties of Ni56-x Mn25Fe x Ga 19 (x = 0, 2, 4, 6, 8) shape memory alloys were investigated using optical microscopy (OM), X-ray diffraction analysis (XRD), differential scanning calorimeter (DSC), and compressive test. It is found that these alloys are composed of single non-modulated martensite phase with tetragonal structure at room temperature, which means substituting Fe for Ni in Ni56Mn 25Ga19 alloy has no effect on phase structure. These alloys all exhibit a thermoelastic martensitic transformation between the cubic parent phase and the tetragonal martensite phase. With the increase of Fe content, the martensitic transformation peak temperature (M p) decreases from 356 C for x = 0 to 20 C for x = 8, which is contributed to the depressed electron concentration and tetragonality of martensite. Fe addition remarkably reduces the transformation hysteresis of Ni-Mn-Ga alloys. Substituting Fe for Ni in Ni56Mn25Ga19 alloy can decrease the strength of the alloys and almost has no influence on the ductility and shape memory property. © 2013 The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg. Source


Xin Y.,North China Electrical Power University | Chai L.,Beijing Key Laboratory for Advanced Functional Materials and Thin Film Technology
Beijing Keji Daxue Xuebao/Journal of University of Science and Technology Beijing | Year: 2013

The microstructure, martensitic transformation behavior, mechanical properties and shape memory characteristics of Ni56Mn25-xFexGa19 (x=0-10) shape memory alloys were investigated by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, differential scanning calorimetry, and compression testing. A single phase of martensite with tetragonal structure is observed in the alloys with x≤4, but dual phases with martensite and face-centered cubic γ phase are present when x≥6. Compared with martensite phase, γ phase is rich in Ni and Fe, and its volume fraction increases with increasing Fe content. The martensitic transformation peak temperature decreases from 356°C for x=0 to 170°C for x=10, which is attributed to the comprehensive effect of the tetragonality and electron concentration of martensite. The introduction of ° phase by substituting Fe for Mn can greatly improve the strength and plasticity of the alloys. However, the shape memory strain drops from 5.0% for x=0 to 2.0% for x=6. Source


Zhang F.,Beihang University | Zhang F.,Beijing Key Laboratory for Advanced Functional Materials and Thin Film Technology | Cui Y.,Beihang University | Cui Y.,Beijing Key Laboratory for Advanced Functional Materials and Thin Film Technology | And 3 more authors.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2013

The microstructure, phase transformation and shape memory properties of Ti69Zr30Fe1 high-temperature shape memory alloy were investigated by optical microscopy (OM), X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and compressive tests. The results show that Ti69Zr30Fe1 alloy is composed of single needle-like α″ martensite with orthorhombic structure at room temperature. During heating process, nano scale ω phases precipitate within the grains at 584°C, and then reverse martensitic transformation from α″ phase to β phase occurs at 615~633°C. When cooling, martensitic transformation occurs from 584 to 529°C. The critical stress of Ti69Zr30Fe1 alloy is about 550 MPa and the maximum shape memory effect (SME) is 2.1%. Copyright © 2013, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved. Source

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