Effect Of Mo Additive On Structure And Magnetic Properties Of Co-Zr Alloys

The purpose of this paper is to search for a new non-rare-earth containing permanent magnetic alloy. High coercivity Co-Zr-Mo permanent magnetic ribbons were well prepared by rapidly quenched technology. In this paper, we had systematically studied the magnetic properties, the phase composition and the coercivity mechanism of the Co-Zr-Mo ribbons. The main experimental results and conclusions are as follows:Co₈₂Zr_18-xMox(0≤x≤5)melt-spun ribbons were successfully produced by rapidly quenched technology at the speed of 40m/s. We had systematically studied the effects of Mo additive on structure and magnetic properties of Co₈₂ Zr₁₈ alloy. From x-ray diffraction analysis, we found that substation of Mo for Co didn't change the crystal structure and the phase composition of the Co₈₂Zr_18-xMo_x(0≤x≤5) melt-spun ribbons. The ribbons were composed of Co₂₃Zr₆ phase, Co₅Zr phase and a little fcc Co phase. Substitution of the relatively larger atomic radius of Mo for Zr leads to a decrease of the Co₅Zr phase lattice. Substitution of Mo for Zr resulted in an increase of their coercivities. Meanwhile, it reduced the magnetization of the melt-spun ribbons. With increasing Mo content, the coercivity of Co₈₂Zr_18-xMo_x (0≤x≤5) melt-spun ribbons increased sharply at first, then decreased. The maximum value of the coercivity, H_c=3.6kOe, was obtained at x=4. The magnetization of the melt-spun ribbons was linearly decreased from 57 to 39 emu/g (under a magnetic field H = 10 kOe) with increasing Mo content from x=0 to x=5 in Co₈₂Zr_18-xMo_x (0≤x≤5) melt-spun ribbons. The hard magnetic phase of the ribbons was believed to be the metastable CosZr phase. From the thermomagnetic curves of Co₈₂ Zr₁₄₄ melt-spun ribbon we found it exhibits a single magnetic transition near 450℃, corresponding to the binary Co₅Zr phase. The Curie Temperature of the Co₈2Zr_18-xMo_x (0≤x≤5) melt-spun ribbons remained basically unchanged with increasing Mo content. Heat treatment of the Co₈₂Zr_18-xMo_x melt-spun ribbons resulted in the change of the structures and magnetic properties. Annealing of the Co₈₂Zr_18-xMo_x (x=0, 2, 4) melt-spun ribbons led to a decrease of the amount of Co₅Zr phase. The amount of Co₂₃Zr₆ phase was increased after annealing. The increase of the coercivity for annealing at relatively low temperatures (500-550℃) was suggested to the grow on the grain size of the Co₅Zr phase. Annealing at relatively high temperatures (600-700℃) resulted in the formation of the soft magnetic Co₁₁Zr₂ phase . In addition, the coercivity mechanism of Co₈₂Zr_18-xMo_x (0≤x≤5) melt-spun ribbons was found to be reverse domain nucleation type.Zr₁₈Co_82-xMo_x(0≤x≤5) melt-spun ribbons were successfully produced by rapidly quenched technology at the speed of 40m/s. We had systematically studied the effects of the substation of Mo for Co on structure and magnetic properties of Co₈₂ Zr₁₈ alloy. From x-ray diffraction analysis, we found that substation of Mo for Co didn't change the crystal structure and the phase composition of the Zr₁₈Co_82-xMo_x (0≤x≤5) melt-spun ribbons. The ribbons were composed of Co₅Zr phase and a little fcc Co phase. The Co₂₃Zr₆ phase wasn't found here. With increasing the Mo content more and more Co₅Zr phase was fount in the XRD. When the Mo concentration was near 5 at%, the Zr₁₈Co₇₇Mo₅ melt-spun ribbon consisted of a single phase of Co₅Zr-type with a maximum coercivity value, H_c=4.1kOe.It confirmed that the hard magnetic phase of the ribbons was the metastable Co₅Zr phase. Substitution of the relatively larger atomic radius of Mo for Co leads to a decrease of the Co₅Zr phase lattice. Substitution of Mo for Co resulted in an decrease in magnetization. Meanwhile, it improved the coercivity of the melt-spun ribbons. With increasing Mo content the coercivity of Co₈₂Zr_18-xMo_x (0≤x≤5) melt-spun ribbons increased sharply in the begin, and then decreased. The maximum coercivity value, H_ε=4.1kOe, was obtained at x=5. The magnetization of the melt-spun ribbons was linearly decreased from 57 to 19 emu/g (under a magnetic field H = 10 kOe) with increasing Mo content from x=0 to x=6 in Co₈₂Zr(18-x)Mo_x (O≤x≤6) melt-spun ribbons. From the thermomagnetic curves of Cos: Zr₁₄Mo₄ melt-spun ribbon we found it exhibits a single magnetic transition near 450℃, corresponding to the binary Co₅Zr phase. The Curie Temperature of the Co₈₂Zr_18-xMo_x (O≤x≤5) melt-spun ribbons decreased monotonously with increasing Mo content. Heat treatment of the Zr₁₈Co_82-xMo_x melt-spun ribbons resulted in the change in the structures and magnetic properties. The coercivity of the Zr₁₈Co_82-xMo_x (x=l, 2, 3) increased slightly with increasing the annealing temperature, then gradually decreased at a relative high temperature. The Zr₁₈Co₇₇Mo₅ melt-spun ribbon contains not only Co₅Zr phase but also some fcc Co phase after annealing. It resulted in a dramatically decrease of coercivity. In addition, the coercivity mechanism of Zr₁₈Co_82-xMo_x (0≤x≤5) melt-spun ribbons was found to be reverse domain nucleation type.