Effects of Nb substitution for Zr on the phases, microstructure and magnetic properties of Co80Zr18−xNbxB2 melt-spun ribbons

► Effects of Nb substitution for Zr in Co80Zr18-xNbxB2 were investigated. ► The added Nb resulted in the decrease of grain size. ► The coercivity depended on the annealing temperature. ► The suitable grain size of Co11Zr2 phase is the reason for increase in coercivity.