Thermomechanical processing effects on the martensitic transformation in Fe-based SMAs

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 Fe40.95Ni28Co17Al11.5Ta2.5B0.05 (at.%) were obtained under the form of melt spun ribbons. The ductility of the specimens was improved by precipitation-hardening heat treatments, meant to enable the occurrence of nanometric-size gamma' particles. The structure of rapidly quenched specimens was analyzed by X-Ray diffraction (XRD) and scanning electron microscopy (SEM). Thermal behaviour was evaluated by differential scanning calorimetry (DSC), from a thermodynamic point of view, aiming to emphasize solid state transitions and by thermomagnetic measurements, from a magnetic point of view, aiming to reveal magnetization dependence on both applied magnetic field and temperature-. Finally, the superelastic behaviour was investigated by micro-indentation. The 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.