Crystallization effect in the self-bias response of several Fe-rich magnetoelastic alloys

This work investigates the self-bias effect in thermally annealed Fe-based magnetoelastic sensors, extending previous findings on Vitrovac® 7600 to compositions designed for enhanced corrosion resistance. The alloys FeNiCrSiB, FeCoSiB, and Metglas were selected to evaluate the influence of annealing-induced crystallization on their magnetic, magnetoelastic, structural, and electrochemical properties, with a focus on their suitability for operation in harsh environments. The results reveal that thermal treatment at 500 °C resulted in partial crystallization, as confirmed by X-ray diffraction and Mössbauer spectroscopy, yielding a dual-phase structure composed of crystalline and amorphous regions. In addition, all treated samples exhibited stable and clearly detectable self-bias magnetoelastic resonances after one month, as well as significant improvements in quality factor (up to 1050 for the FeCoSiB alloy) and frequency stability over time (maximum deviation down to 6 and 12 Hz for the Metglas and FeCoSiB sensors, respectively). Further, while thermal annealing adversely affected the corrosion resistance of V7600 and FeCoSiB (increase in the corrosion rate of 76% and 660%, respectively), it preserved the stability of Metglas and substantially improved the performance of FeNiCrSiB (55% reduction in corrosion rate). These results highlight the potential of Cr- and Ni-enriched Fe-based alloys as suitable candidates for self-bias magnetoelastic sensor platforms to be employed in harsh environments.