Phase transformation, thermal behavior and magnetic study of new Co80-xTaxSi5C15 (x = 0, 5) glassy/nanocrystalline alloys prepared by mechanical alloying

In the current work, new Co80-xTaxSi5C15 (x = 0, 5) alloys were prepared by mechanical alloying (MA) and the influence of milling period on their microstructure, thermal behavior, and soft magnetic properties were examined. The quantitative X-ray diffraction (XRD) analysis, revealed that while the fraction of hexagonal-close packed (hcp) Co-based solid-solution continuously declines by milling time, the content of face-centered cubic (fcc) one initially levels up and subsequently decreases. Furthermore, the microalloying with Ta markedly enhances the amorphization rate, as well as the fraction of amorphous phase from 60 wt% for Co80Si5C15 alloy to near 100% for Co75Ta5Si5C15 alloy after 120 h milling. Thermal analysis reflected the absence of supercooled liquid region (SLR) in Co80Si5C15 alloy, while Co75Ta5Si5C15 alloy shows a relatively wide SLR, with an extension of 41 K, demonstrating its high thermal stability. Magnetic measurements showed that the soft magnetic behavior of both alloys notably improves upon a certain stage of milling. It was shown that the new Co75Ta5Si5C15 glassy alloy represents a promising soft magnetic behavior, i.e., a minimum coercivity (H-c) of 1.2 kA/m, which is notably lower than a minimum value obtained for Co80Si5C15 (3.3 kA/m), as well as those reported for most other Co-based amorphous/nanocrystalline alloys prepared by MA. (C) 2020 Elsevier B.V. All rights reserved.