Composition dependence of the microstructure and soft magnetic properties of Fe-based amorphous/nanocrystalline alloys: A review study

The intention of the present study is to review and compare the effect of various well-studied alloying elements on the microstructure and soft magnetic properties of the Fe-based amorphous/nanocrystalline system. The state-of-the-art Fe-based amorphous/nanocrystalline alloys have been developed because of their unique soft magnetic properties such as low core loss, high permeability(104-105 at 1 kHz) and low magnetostriction (< 10 ppm) as compared to conventional silicon steels which are also called electrical steels. In Fe-based amorphous/nanocrystalline system, the chemical composition and microstructural features particularly grain size play an indispensable role on the saturated magnetization (Bs) and coercivity (Hc) values. An ideal Fe-based soft magnetic material is defined as a material possessing higher Bs and lower Hc. The problem of the new material is its low Bs value (for commercial material is 1.4 T) than silicon steels (≈ 2 T). In addition to Bs content of new material, many attempts have been made to reduce the Hc value which could be achieved via a decrease of grain size (< 50 nm). To reach this goal (Bs↑ and Hc↓), the effect of a variety of elements on the microstructure, crystallization process and soft magnetic properties of the Fe-based amorphous/nanocrystalline alloys has been investigated so far. The aim of all these studies is to find an appropriate replacement for conventional silicon steels because of their high core loss and low permeability. Effect of alloying elements including Si, B, Cu, Nb, Zr, N-doping, P, Ni, Co, H-doping, Ge and W on the microstructure and magnetic properties is the main subject of this study in order to shed light on the dependence of magnetic properties with composition and grain size. © 2014 Elsevier B.V

Stress-relaxation heat treatment in FeSiBNb amorphous alloy: Thermal, microstructure, nanomechanical and magnetic texture measurements

Abstract In the present study, the effect of stress-relaxation treatment (Tstress-relaxation &lt; Tglass transition) on the magnetic texture, nanomechanical properties, and variation of free-volume in FeSiBNb amorphous alloy was investigated using Mössbauer spectroscopy, nanoindentation, dynamic mechanical analysis (DMA), and positron annihilation lifetime spectroscopy (PALS) techniques. It was shown that stress-relaxation treatment slightly improved the magnetic texture by 6% at T ≪ T g due to small-scale displacement of atoms whereas the magnetic texture was deteriorated due to thermal treatment at temperatures around the glass transition point (large-scale displacement of atoms). According to nanoindentation results, the hardness (H) and reduced modulus (Er) of the amorphous ribbon increased by 15% and 13%, respectively, after stress-relaxation treatment at 716 K for 5 min. Increasing the stress-relaxation time from 5 min to 60 min at 716 K resulted in decreases in the hardness and reduced modulus which are attributed to the increase of free-volume defects (increase of τ2 lifetime measured by PALS). Transmission electron microscopy (TEM) showed the formation of extremely fine embryos of α-Fe (3–5 nm in size) after stress-relaxation treatment