【作者】 张金宝；

【导师】 王文全；

【作者基本信息】 吉林大学 ， 凝聚态物理， 2010， 博士

【摘要】 本文在全面评述永磁材料的基础上,采取快淬工艺成功制备出了一系列高矫顽力的Co-Zr基永磁合金薄带,对其相组成、微结构、硬磁性质和矫顽力机制进行了详细研究。一方面,利用Mo元素添加,获得了具有单Co5Zr相的条带样品,进一步拓宽了合金的成分范围,得到了富Co区Co-Zr合金具有单Co5Zr相结构的成分组成,详细分析了其结构与磁性的关系,发现Co5Zr是合金的硬磁性相,该相的含量与平均晶粒尺寸是决定矫顽力大小的主要因素,证明了Co-Zr-Mo合金条带的矫顽力机理为反磁化核的形核机制。此外,还利用分裂能带模型分析了部分样品的低温磁矩。另一方面,利用B和Mo元素进行联合添加,获得了目前Co-Zr系统合金的最大矫顽力,通过对其微结构的分析,发现Co-Zr-B-Mo合金条带的高矫顽力与其独特的微结构有密切的关系,结合磁性测量的结果,证明了Co-Zr-B-Mo合金条带的矫顽力机理为面缺陷控制下的非均匀畴壁钉扎。更多还原

【Abstract】 In this thesis, formation, structural and magnetic properties of the non-rare-earth containing Co-Zr system alloys have been investigated, based on the review of the research and development of permanent magnetic materials, using melt-spun technology and element additive method. The purpose of this paper is to search for new permanent magnetic materials without rare earth. Furthermore, the coercivity mechanism of such permanent magnets is studied also.1. Co-Zr alloy ingots were prepared by arc melting and the melt-spun ribbons were successfully produced by rapidly quenched technology. We had systematically studied the structure and magnetic properties of those alloys.From x-ray diffraction analysis of Co_100-xZr_x（x=16～20）alloy ingots and those melt-spun ribbons, we find that alloy ingots are composed of face-centered cubic Co, Co₂₃Zr₆,Co₅Zr and Co11Zr2 phase, while the melt-spun ribbons are composed of face-centered cubic Co, Co₂₃Zr₆ and Co₅Zr phase. Further analysis show that the more Co₅Zr phase the ribbon contains, the larger the coercivity it has. This indicates that the hard magnetic phase in Co-Zr alloy is Co₅Zr phase. This result has clarified the controversy for the hard magnetic phase in Co-Zr alloys and provided a basic research for further study of Co-Zr alloys. By the analysis of magnetic properties on the binary Co-Zr alloy samples with different components and quenching rates, we have obtained the optimized coercivity values of the component and quenching rate. The purpose of this work is to further study of Co-Zr alloys by additive. We had attempted to study magnetic properties of Co-Zr alloys by transition metal additive. It has been first found that the coercivity of Co-Zr alloy could be significantly enhanced by a small amount of Mo additive. From x-ray diffraction analysis of Co_82-xZr₁₈Mo_x（x=1～5） alloy ribbons, we find that the melt-spun ribbons were composed of face-centered cubic Co and Co₅Zr phase. With the increasing of Mo content, the mount of Co₅Zr phase in those ribbons increases also. When the Mo content is up to 5%, the ribbons with nearly single Co₅Zr phase structure had been first found.2. We had systematically studied the effects of Mo additive on structure and magnetic properties of Co-Zr alloy.From thermo magnetic analysis of Co-Zr-Mo system alloy ribbons, we find that the Curie temperature of Mo doped Co₅Zr phase is about 450°C. The high Curie temperature suggests that Co-Zr permanent materials have potential applications for high temperature. The x-ray diffraction analysis and magnetic measurement of those ribbons show that Mo additive leads to a decrease of the magnetization measured in the field of 10kOe. While Mo additive plays an important role in increasing the mount of Co₅Zr phase, refining the grain size and enhancing coercivity. Those results confirm that the hard magnetic phase in the Co–Zr-Mo alloys is of Co₅Zr phase. The influence of quenching rate on the magnetic properties of Co-Zr-Mo melt-spun ribbons had been investigated. It is found that with the increasing of quenching rate, the coercivity increases linearly. The reason for this case is that with the increasing of quenching rate, the mount of minor phase (Co₂₃Zr₆) and the grain size of major phase （Co₅Zr） will decrease sharply. The influence of annealing on the magnetic properties of Co-Zr-Mo melt-spun ribbons had been investigated. It is found that annealing will lead to coercivity change by the change of the mount of Co₅Zr phase and the grain size of this phase. According to magnetizing field dependence of coercivity, the coercivity mechanism is controlled by the nucleation of the reversed domain.We had broadened and refined the range of compositions studies to systematically study the structure and magnetic properties of Co-Zr-Mo melt-spun ribbons. From x-ray diffraction analysis of Co_100-x-yZr_xMo_y （x=15.5～18.5,y=4.0～6.5） melt-spun ribbons, we find that the major phase is Co₅Zr and minor phase is Co together with Co₂₃Zr₆. The composition range of the ribbons with nearly single Co₅Zr phase structure is x=18.0 y=5.0～6.0, x=16.5～18.0 y=5.5 and x=18.5 y=5.0. Coercivity, magnetization measured in the field of 10kOe and mean grain size of Co₅Zr phase as a function of composition of Cobalt-rich Co-Zr-Mo melt-spun ribbons were investigated. We can see that when the atomic proportion of Co Mo and Zr is near at 5:1, the ribbons will have the maximum coercivity value （4.7kOe）. In comparison with the maximum coercivity value （3.6kOe） of the binary Co-Zr alloy, the maximum coercivity value increases near 30%. We had systematically analyzed the factors which affected the coercivity. We find that the effect of the mount of Co₅Zr phases is much less important than that of grain size. The meaning of this result is the confirmation that decrease of grain size is a effective method to increase coercivity. This study provides a method to further improve their magnetic properties.We had investigated the low temperature magnetic properties of some Co-Zr-Mo melt-spun ribbons. We find that the coercivity of the ribbons at low temperature are significantly higher than that of the ribbons at room temperature, that is to say, temperature dependence of coercivity is abnormal. According to magnetization measured in the field of 10kOe at low temperature （-196℃） dependence of composition, we find that experimental results can be in good agreement with the virtual bound state model.3. According to the theory of amorphous, the larger the difference in the size of constituent atoms, the easier the amorphous formed. So, small B atom is introduced into the Co-Zr-Mo alloys in an attempt to reduce the grain size and increase consequently the coercivity. The structure and magnetic properties of Co-Zr-B-Mo melt-spun ribbons had been studied.The largest coercivity of 7.0kOe ever for Co-Zr based alloys is observed on Co₇₇Zr₁₆B₂Mo₅ ribbons by the melt spinning. In addition, magnetization measured in the field of 10kOe increases with the increasing of the B content. From x-ray diffraction analysis of Co₇₇Zr_18-xB_xMo₅（x=0.5～4.0）melt-spun ribbons, we find that the ribbon of x=4.0 is amorphous. In the other ribbons major phase Co₅Zr and minor phase Co of face-centered cubic structure are coexist. According to thermo magnetic analysis and AC magnetic susceptibility measurements of Co-Zr-B-Mo melt-spun ribbons, we find that the Curie temperature of major phase is about 450°C, which is nearly unchanged with the increasing of the B content. The influence of annealing on the magnetic properties of Co-Zr-B-Mo melt-spun ribbons had been investigated. It can be seen that annealing at low temperature will lead to coercivity increase insignificantly while annealing at high temperature will lead to coercivity decrease significantly.The microstructure of Co₇₇Zr₁₆B₂Mo₅ melt-spun ribbons had been investigated by the transmission electron microscopy. The ribbons are of multi-crystalline structure. There are many blocky grains in the ribbons. Length and width of the grains are about a few hundred nanometers and the thickness of the grains is about several tens of nanometers. Each grain has the alternating light and dark lamellar structure, which suggests that the grains have high density of planar defects. The thickness of the planar defects is 2～5 nm. The spots in the Selected area electron diffraction（SAD）pattern demonstrate the characteristics of single crystal diffraction, but there is a broadened ring, suggesting that the ribbons is a partial crystal structure. The high coercivity may be related to the unique micro-structure of Co₇₇Zr₁₆B₂Mo₅ melt-spun ribbons.The coercivity indicates the ability of resisting the reversal field for a permanent magnets and the coercivity mechanism is key problem in permanent magnets. According to magnetizing field dependence of reduced remanence and coercivity and Henkel Plot, the coercivity mechanism is controlled by inhomogeneous domain pinning with planar defects. Unfortunately, it is impossible to calculate the theoretical coercivity according to the planar defects model because many parameters, especially in the planar defects, are unknown.更多还原