Composition Design and Ageing of Ni-Mn-Ga Alloys

Abstract:

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Ni-Mn-Ga ferromagnetic shape memory alloys (FSMA) are a potential new class of actuator materials able to respond at higher frequencies (at least 300 Hz) with comparable strains (up to 6 %) in a moderate field (below 1 T)[1]. Magnitude of the strain depends on the values of several critical material parameters, most importantly the martensitic transformation temperature (TMart), Curie temperature (TC) and saturation magnetization (MS)[2]. It is well known that these parameters are strongly dependent on the composition of the alloy. Composition dependence of TMart, TC and MS have been experimentaly explored [3,4]. Therefore, it is possible to compile a more complete, and hence more useful composition map for designing Ni-Mn-Ga FSMAs. Ageing behavior is important in these newly developed FSMAs because ageing can affect the reliability of devices using the alloys. Ni-Mn-Ga FSMAs and Au-Cd[5] alloys have several important common characteristics, including off-stoichiometry alloy composition (designed for operation at ambient temperature) and easy twin boundary motion in the martensite state, thus similar ageing behavior is expected in Ni-Mn-Ga alloys. Ni-Mn-Ga alloys have also demonstrated strong damping due to the motion of twin boundaries[6]. Low-frequency mechanical properties are typically measured using the technique of dynamical mechanical analysis (DMA)[7]. In this paper, we present studies of composition design, subtle structure changes associated with ageing, and the temperature dependence of the low-frequency mechanical properties of several Ni-Mn-Ga single crystal alloys.

Info:

Periodical:

Materials Science Forum (Volumes 449-452)

Edited by:

S.-G. Kang and T. Kobayashi

Pages:

1313-1316

DOI:

10.4028/www.scientific.net/MSF.449-452.1313

Citation:

X. J. Jin et al., "Composition Design and Ageing of Ni-Mn-Ga Alloys ", Materials Science Forum, Vols. 449-452, pp. 1313-1316, 2004

Online since:

March 2004

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$35.00

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