Study Of Hard Magnetic Properties And Phase Structure On The Non-rare-earth Containing Co-Zr System Alloys

High coercivity Co-Zr-Mo-B melt-spun ribbons were produced by rapidly quenched technology. In this article, we studied the magnetic properties, the phase composition and the mechanism of the coercivity of the ribbons prepared. We used the Fe to substitute the Co to improve the magnetic properties and studied the Co-Zr-Mo-B-Fe melt-spun ribbons systematically. We got conclusions as follows:Co₈₀Zr_18-xMo_xB₂(1≤x≤4) melt-spun ribbons were made by rapidly quenched technology at a speed of 40m/s. The effects of Mo additive on the magnetic properties of Co-Zr-B alloys were studied systematically. The melt-spun ribbons were measured by VSM, when the content of the Mo reached 2%, we got the maximum coercivity value of Hc=6.3kOe. From x-ray diffraction analysis, we found that the XRD patterns of the Co₈₀Zr_18-xMo_xB₂(1≤x≤4)melt-spun ribbons were indexed to the Co₅Zr, Co23Zr6 and fcc-co phases, and the addition of Mo made the the Co₅Zr phase much stronger, But it was not the case that the more Mo the better. As the maximum coercivity value of Co₈₀Zr_18-xMo_xB₂(1≤x≤4)melt-spun ribbons existed in Co80Zr16Mo2B2. This might be due to the respective proportion of each phase. When the proportion of each phase reached a proper rate, the coercivity reached the maximum value.We all kown that, the quenching rate contribute much on the magnetic properties, if it is too slow, the grain size will be too large, and if it is too fast will make it amorphous.In this article ,we took the Co₈₀Zr₁₆Mo₂B₂ for example to study the effect of the quenching rate on the magnetic properties. We found that, when we made the quenching rate at 40m/s, the alloys performed the best magnetic properties. These ribbons were annealed at temperatures between 500℃to 700℃for 30 min. We also took the the Co80Zr16Mo2B2 for example to continue our study. After the annealed ribbons were measured by VSM, we found the coercivity decreased at the temperature 500℃. There is then an increase in the coercivity to a maximum value of Hc=6.8kOe for T=600℃, and it decreased again for T=650℃and 700℃. X-ray diffraction analysis was carried out. We found that Co11Zr2 phase, which was considered to be soft phase,appeared when the melt-spun ribbons were annealed at 650℃and 700℃, which was supposed to be the reason for the decrease of the coercivity. From the SEM analyses, we found that heat treatment brought an increase in the grain size. It was concluded that heat treatment could bring to fine microstructure that made a larger coercivity. And the best annealing temperature was 600℃. Meanwhile we studied the coercivity mechanism of the Co80Zr16Mo2B2 melt-spun ribbons, and the coercivity was governed by pinning model. Theδm was measured by VSM. The positiveδm reflect that strong exchange-couple existing in the ribbons, and after annealed at 600℃, the exchange-couple seemed to be even much stronger.Co_80+xZr_16-xMo₂B₂(x=1,2,3,4) melt-spun ribbons were made by rapidly quenched technology at a speed of 40m/s. We found that the value of the Ms was improved significantly, as the content of the Co increased, but compared with the Co₈₀Zr_18-xMo_xB₂(1≤x≤4)melt-spun ribbons, the value of Hc decreased a lot, the total magnetic properties were not so good. From the XRD, we saw the ribbons were indexed to the Co5Zr, and fcc-co phases, and the fcc-co phase was much stronger. The Co_80+xZr_16-xMo₂B₂(x=1,2,3,4) melt-spun ribbons were then annealed between 550℃-700℃for 30 min. From the VSM, we saw the coercivity increased little, while the (BH)max decreased a lot. It was concluded that the content of Co in the Co-Zr-Mo-B alloys could not be much high. Also strong exchange-couple existing in the ribbons of Co₈₁Zr₁₅Mo₂B₂, but the value ofδm was minus.Co_80-xZr₁₆Fe_xMo₂B₂ (x=1,2,3,4) ribbons were made by rapidly quenched technology at a speed of 40m/s. The melt-spun ribbons were studied by VSM, the Ms increased with the content of the Fe, because the Ms of Fe is larger than that of Co. The Mr/Ms of the ribbons was above 0.8, we supposed strong exchange-couple existed in the ribbons, but the coercivity of the melt-spun ribbons decreased significantly as the content of Fe increased, it made the value of the (BH)_max small. From the XRD, we found fcc-co phase and weak Co5Zr phase, this could explain the bad performance.We did not make further study of this system due to the poor magnetic properites.