Microstructures of Co–Zr–B alloys produced by melt-spinning technique

•High-coercivity Co–Zr–B alloys were produced by melt-spinning.•TEM studies revealed that the Co–Zr–B alloy had the very fine CoxZr (x ≈ 5) grains.•The origin of the high coercivity in this alloy was found to be the CoxZr (x ≈ 5) phase.

The microstructures of high-coercivity Co–Zr–B melt-spun ribbons were examined in order to determine the hard magnetic phase in the Co–Zr–B alloys. Throughout X-ray diffraction (XRD) and magnetic studies, as well as microstructural studies by scanning electron microscope (SEM), transmission electron microscope (TEM), and scanning transmission electron microscope (STEM), no Co5Zr phase was found in the Co–Zr–B melt-spun ribbons. Only the CoxZr (x ≈ 5) phase was detected, indicating that the hard magnetic phase in the Co–Zr–B alloys was the CoxZr phase. The TEM and STEM studies revealed that the Co–Zr–B alloys had very fine CoxZr grains of around 200 nm in diameter and that the hard magnetic CoxZr phase was surrounded by the soft magnetic Co grain boundary phase.