Magnetic field intensity dependent microstructure evolution and recrystallization behavior in a Co–B eutectic alloy

Systematic understanding on the magnetic field intensity dependent microstructure evolution and recrystallization behavior in a Co–B eutectic alloy under a constant undercooling (∆T≈100 K) were carried out. Absent of the magnetic field, the comparable size of divorced FCC–Co and Co₃B eutectic ellipsoidal grains coexist with a few regular lamellas. When the magnetic field is less than 15 T, the elongated primary FCC–Co dendrites parallel to the magnetic field with the dispersed FCC–Co nano–particles embedded within the Co₃B matrix occupy the inter–dendrite regions. Once the magnetic field increases to 20 T, the FCC–Co/Co₂B anomalous eutectic colonies dominate. The formation mechanism of Co₂B phase is discussed from several aspects of the competitive nucleation, the chemical redistribution induced by the thermomagnetic–induced convection and magnetic dipole interaction, and the strain–induced transformation. Furthermore, the application of magnetic field is found to promote recrystallization, proved by the lower density of misorientation, the appearance of FCC–Co annealed twins and more Co₃B sub–grains. This work could further enrich our knowledge about the magnetic–dependent microstructure evolution and recrystallization process in the undercooled Co–B system and provide guidance for controlling the microstructures and properties under extreme conditions.