Sintering behaviour of magnetic bulk glassy cores obtained from Fe71Nb3.7Cu1Al3Mn0.8Si13.5B7 alloy powder

Abstract

The sintering behaviour of magnetic bulk glassy compact has been addressed. Rapidly quenched ribbons of Fe71Nb3.7Cu1Al3Mn0.8Si13.5B7 alloy were ball milled to powder and consolidated using binder to get bulk glassy compacts. Structural and crystallization behaviour of glassy and heat-treated powders was evaluated. Differential scanning calorimetry (DSC) of the powders showed transition from amorphous to nanocrystalline phase at 800 K. Magnetic evaluation of the bulk glassy cores revealed best soft magnetic property at a sintering temperature of 775 K which was due to the formation of α-Fe(Si,Al) and Fe3(Si,Al) nanoparticles evidenced by transmission electron microscopy (TEM) and X-ray analysis. However, at this temperature the glassy compact exhibited low value of remanence, which was attributed to the demagnetization field due to porosity in the material that developed from the escaped mineral binder. At subsequent higher sintering temperature of 785 K the glassy core exhibited inferior soft magnetic properties with a low coercivity due to the formation of strongly anisotropic boride phases. Remanence value increased due to reduced demagnetization effect arising from a more compact morphology. Such reduced porosity was due to the coalescence of powder particle as observed from scanning electron microscopy (SEM).