Structure and magnetic properties of magnetostrictive rapidly-quenched alloys for force sensors applications

Abstract

This work was aimed at investigating the FeNiMoB type alloys exhibiting relatively high saturation magnetostriction after suitable heat treatment, which makes them suitable for application in force sensors. Crystallization process of amorphous alloy was examined by DSC. Temperatures and enthalpies of both stages of crystallization were determined from DSC upon continuous heating from a room temperature to 993 K with constant heating rate of 20 K/min. Next, samples were isothermally annealed under longitudinal and transverse magnetic fields within the temperature range of 623–833 K for 1 h under Ar protective atmosphere. Structure of the alloys was checked by means of XRD and TEM. After annealing, the AC (50 Hz) magnetic properties (coercivity, magnetic induction) were determined using a computerized hysteresis loop tracer. An effect of the annealing temperature, induced magnetic anisotropy and of the applied compressive stresses on the dynamic magnetic properties of the alloys was studied within a frequency range from 50 Hz to 50 kHz. Our studies confirmed that the Fe-Ni-Mo-B alloy annealed at 653 K is the most suitable for application in force sensors. Moreover, the results obtained indicate that for the measurements of compressive stresses below 0.3 MPa it is more advantageous to use the cores with longitudinal anisotropy, whereas the cores with a transverse magnetic anisotropy are more suitable for application at the compressive stresses over 0.3 MPa.