Factors Influencing the Structures and Proprieties of Polycrystalline Magnetic Fe-Ni-Co-Al-Ta-B Shape Memory Alloys

Magnetic shape memory alloys (MSMAs) belonging to Fe-Ni-Co-Al system have been recently developed due to their small temperature dependence of superelastic and magnetic properties, which renders great potential for practical applications. Specimens of Fe_40.95Ni₂₈Co₁₇Al_11.5Ta_2.5B_0.05 (at.%) were obtained under the form of melt spun ribbons and vacuum induction melt ingots, respectively. The ductility of specimens was improved by precipitation hardening heat treatments, which enabled the occurrence of nanometric-size γ’ particles. The structure of both rapidly quenched and bulk specimens was analyzed by X-Ray diffraction (XRD) and scanning electron microscopy (SEM). Thermal behavior was evaluated by differential scanning calorimetry (DSC), from a thermodynamic point of view and by thermomagnetic measurements, from a magnetic point of view. Finally, superelastic behavior was revealed in association with anelastic effect, determined by the variation rate in time of the average dimension of Vickers microhardness induced indentation. Experimental data allowed analyzing the influence of various factors, such as alloy structure (bulk and rapidly quenched), thermomechanical processing (hot rolling, heat treatment) and precipitation hardening temperature on the structure and properties of Fe-Ni-Co-Al MSMAs.