Magnetic properties and thermal stability of the soft magnetic alloy (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 nanocrystallized in the presence of an alternating magnetic field

Resumo

For the purpose of developing materials with optimum magnetic properties for high-temperature applications (500–600°C), we have investigated the magnetic properties and structure of a nanocrystalline (Fe_0.7Co_0.3)₈₈Hf₄Mo₂Zr₁B₄Cu₁ alloy. The alloy was subjected to nanocrystallizing annealing (NA) at 620°C in the presence of an alternating magnetic field (magnetic heat treatment, MHT). The influence of the duration of the NA and of the amplitude value H_amp of the ac magnetic field on the magnetic properties of the alloy and on their thermal stability has been studied. It has been established that the MHT carried out at 620°C is most efficient after holding in a magnetic field for 20 min. In this case, a decrease in the coercive force and an increase in the remanence have been observed. An increase in the time of the holding upon the MHT from 20 min to 4 h decreases the efficiency of the treatment. It has been shown that the MHT carried out at 620°C for 2 h and H_amp = 9 kA/m leads to the smallest changes in the magnetic properties of the alloy after the subsequent holding at a temperature of 550°C for 30 h. However, this treatment does not ensure the thermal stability of the magnetic properties of the alloy at 550°C achieved earlier after the nanocrystallization of the alloy at 620°C for 20 min in the presence of tensile stresses (250 MPa).