Elastic and Superelastic Properties of NiFeCoGa Fibers Grown by Micro-Pulling-Down Method

Abstract

Low-frequency elastic modulus, internal friction, tensile stress-strain loops, and thermally-induced strain recovery of single-crystal fibers obtained by pulling-down method from the melts of NiFeGaCo alloys were studied. A minimum of the elastic modulus and the maximum peak of the internal friction were obtained at the martensitic transition temperature. A large super-elastic strain of about 10% was obtained in the fiber of the Ni 49 Fe 18 Ga 27 Co 6 alloy. Thermodynamic estimation by the Clausius-Clapeyron equation was consistent with the experimental results.

Effect of chemical ordering annealing on martensitic transformation and superelasticity in polycrystalline Ni–Mn–Ga microwires

“…In addition, the slopes of part IV decrease with increasing temperature, which is consistent with Ni-Mn-Ga single crystals and other FMSMAs such as Ni-Fe-Ga and Ni-Fe-Co-Ga [19,40,42,43]. The reduced mobility of the martensite at low temperature contributes to the increase in martensite elastic modulus [40].…”

“…The temperature dependence of the SIM stress (r Ms /dT $ 7.6 MPa/K) in the present microwires is larger than that in Ni-Mn-Ga single crystals ($2.8 MPa/K along [0 0 1] and $5.2 MPa/K along [1 1 0]) [11,41] and in some other ferromagnetic shape memory single crystals ($2.1 MPa/K in Ni-Mn-Co-In and $1.4 MPa/K in Ni-Fe-Co-Ga) [42,44]. Besides, the temperature dependence of SIM stress in other conventional polycrystalline superelastic alloys are presented in inset (I).…”

“…Fig. 9 compares the r Ms vs temperature diagrams with respect to Ni-Mn-Ga microwires from our previously work [19], Ni-Mn-Ga single crystals [11,41], other FESMAs single crystals [42,44] and the present Ni-Mn-Ga microwires. Clearly, Ni-Mn-Ga single crystals possess lower temperature dependence than polycrystalline alloys.…”

Destabilization of Ni–Mn–Ga martensite: Experiment and theory

“…3), that is typical e.g. for the Co-Ni-Ga and Ni-Fe(Co)-Ga single crystals [28,29]. On the contrary, it brings about an opposite effect, hereafter termed as the martensite destabilization (rejuvenation).…”

Magnetoelastic Anomalies Exhibited by Ni–Fe(Co)–Ga Polycrystalline Ferromagnetic Shape Memory Alloy

“…The present work supports the point of view proposed Chen et al 22) that the difference in strain behavior is related to the parameter c/a. According to this point of view, the alloys with c/a < 1 suffer a spontaneous contraction 23,24) while those with c/a > 1 present an expansion 22,25) during the transformation from the parent phase to the martensitic one which is the case of the studied sample in the present work. Just described correlation between strain behavior and c/a ratio could be considered as an empirical fact which is still needed to be confirmed and understood by further more focused studies.…”