The characterization of structure, thermal stability and magnetic properties of Fe-Co-B-Si-Nb bulk amorphous and nanocrystalline alloys

Recently bulk amorphous alloys have attracted great attention due to their excellent magnetic properties. The glass-forming ability of bulk amorphous alloys depends on the temperature difference (Delta T-x) between glass transition temperature (T-g) and crystallization temperature (T-x). The increase of Delta T-x causes a decrease of the critical cooling rate (V-c) and growth of the maximum casting thickness of bulk amorphous alloys. The aim of the present paper is to characterize the structure, the thermal stability and magnetic properties of Fe36Co36B19Si5Nb4 bulk amorphous alloys using XRD, Mossbauer spectroscopy, DSC and VSM methods. Additionally the magnetic permeability mu(i) (at force H approximate to 0.5A/m and frequency f approximate to 1 kHz) and the intensity of disaccommodation of magnetic permeability Delta mu/mu(t(1)) (Delta mu=mu(t(1) = 30s)-mu(t(2) = 1800 s)), have been measured, where mu is the initial magnetic permeability measured at time t after demagnetisation, the Curie temperature T-C and coercive force H-c of rods are also determined with the use of a magnetic balance and coercivemeter, respectively. Fe-Co-B-Si-Nb bulk amorphous alloys were produced by pressure die casting with the maximum diameters of 1mm, 2mm and 3mm. The glass transition temperature (T-g) of studied amorphous alloys increases from 807K for a rod with a diameter of 1mm to 811K concerning a sample with a diameter of 3mm. The crystallization temperature (T-x) has the value of 838K and 839K for rods with the diameters of 1mm and 3mm, respectively. The supercooled liquid region (Delta T-x = T-x - T-g) has the value of about 30 K. These values are presumed to be the origin for the achievement of a good glass-forming ability of the Fe-Co-B-Si-Nb bulk amorphous alloy. The investigated amorphous alloys in the form of rods have good soft magnetic properties (e. g. M-s = 1.18-1.24 T). The changes of crystallization temperatures and magnetic properties as a function of the diameter of the rods (time of solidification) have been stated. (C) 2010 Elsevier B. V. All rights reserved.