Liquidus projection of the cobalt-rich Co–Si–B system

Abstract

Cobalt-rich amorphous metallic alloys (AMAs) are highly valued for their superior magnetic properties and corrosion resistance in high-precision applications. However, the development of these metastable systems is often hindered by a lack of fundamental thermodynamic data, particularly regarding the crystalline phases that compete with glass formation. This study investigates the phase equilibria of the Co-rich region of the Co–Si–B ternary system to propose a comprehensive liquidus projection. A series of Co–Si–B alloys were synthesized via arc melting and characterized in the as-cast state using XRD, SEM-BSE, EDS, and EBSD. The experimental results enabled the identification of ten primary precipitation fields, including \(CoB, C{o}_{2}B, \alpha C{o}_{2}Si, CoSi\), and the ternary Co_4.75Si₂B phase and the determination of several monovariant lines and ternary invariant reactions. Key findings include the identification of three thermal maxima (m1, m2, m3) along monovariant lines and the characterization of the Co_4.75Si₂B ternary phase, which was found to form via an incongruent peritectic reaction (\(L + \alpha Co_{2} Si \Leftrightarrow Co_{{4.75}} Si_{2} B\)). Furthermore, the solidification paths of various alloys were traced to map the trajectories toward ternary eutectic points. The resulting liquidus projection provides a critical experimental framework for predicting solidification behavior and enhancing the manufacturing of Co-based metallic glasses.