Characterization, thermodynamic analysis and magnetic investigation of new soft magnetic amorphous/nanocrystalline Co50Fe21Ti19Ta5B5 powders produced by mechanical alloying

In this work, the microstructure, thermal stability and magnetic properties of a new Co50Fe21Ti19Ta5B5 alloy prepared by mechanical alloying (MA) were investigated. Quantitative X-ray diffraction (XRD) analysis performed via Rietveld refinement demonstrated a high glass-forming ability (GFA) of this alloy through a fast amorphization with a glass fraction of about 98 wt% after 20 h milling. In addition, a large driving force for amorphization in Co50Fe21Ti19Ta5B5 alloy was indicated via a great difference between the Gibbs free energy changes for amorphization (-68 kJ/mol) and solid-solution formation (-6 kJ/mol), calculated based on the extended Miedema's semi-empirical model. Thermal analysis confirmed a higher crystallization temperature of new alloy compared to some of mechanically alloyed Co-based glassy powders, recently produced. The presence of few remained nanocrystals with an average size of 5 nm and little un-dissolved boron nanoparticles inside the amorphous matrix were confirmed by high-resolution transmission electron microscopy (HRTEM) measurements. The magnetic measurements revealed that the powders after an optimized milling time and annealing condition show a promising magnetic softness. The new powders exhibited a larger saturation magnetization (78 Am2/kg) and significantly a lower coercivity (0.2 kA/m) with respect to the most of the Co-based amorphous powders prepared by MA. (c) 2018 Elsevier B.V. All rights reserved.