【作者】 查五生；

【导师】 涂铭旌；

【作者基本信息】 四川大学 ， 材料学， 2004， 博士

【摘要】 在总结和分析纳米晶双相复合永磁材料交换耦合作用机理及其磁性能影响因素的基础上,采用熔体快淬加后续晶化退火的方法制备了多个系列的稀土铁系永磁粘结磁体,并用XRD、AFM、DTA及TEM等手段,比较系统地研究了制备工艺参数、合金稀土含量及掺杂元素的添加对合金显微组织结构、磁性相的本征磁学性质及合金磁性能的影响规律和影响机理。合金快淬态结晶度显著影响其晶化后的晶粒大小和均匀性。以24,26,28和30m/s快淬的(Nd0.8Pr0.2)10.5Fe77.5Co5Zr1B6合金,快淬态薄带由非晶和部分微晶组成。快淬速度越高,快淬态薄带结晶度越低。含有微晶的快淬态薄带,退火时新相非均匀形核析出。以26m/s快淬的、结晶度约为30%的薄带,新相析出的形核率较高,可获得细小、均匀的显微组织结构,合金具有较佳的综合磁性能。结晶度过高,形核率降低,且微晶的长大使显微组织结构不均匀;结晶度过低,新相析出形核以均匀形核为主,形核率较低,显微组织结构较均匀,但平均晶粒尺寸较大。晶化退火温度和时间也直接决定磁体的磁性能。在700℃下退火10min,磁性相析出充分,晶粒均匀细小,磁体综合磁性能较佳。温度低于700℃,或时间少于10min,磁性相析出不完全;温度高于700℃,或时间多于10min,磁性相析出充分,但晶粒会进一步长大。随稀土含量的降低,(Nd0.8Pr0.2)xFe88-xCo5Zr1B6合金的软磁相含量增加,合金的剩磁Br增加,而内禀矫顽力Hci和最大磁能积(BH)m下降。10%是合金磁性能发生较大变化的临界稀土含量。低于这一含量,合金的内禀矫顽力非常低。这一实验结果与完全耦合软磁相体积分数计算示意模型的计算结果吻合较好。依据完全耦合软磁相体积分数计算示意模型,计算出软磁相的临界体积分数<WP=5>为～20%。若软磁相的体积分数超过这一理论值,则会存在部分软磁相不被硬磁相完全耦合,成为整个磁体反向磁畴的核心。随(NdxPr1-x)10.5Fe77.5Co5Zr1B6合金中Pr含量x的增加,磁体的Hci单调上升,Br单调下降,(BH)m在x=0.8处达到最大值70.6kJ/m3。该系列合金Pr替代Nd的最佳分数为0.8。Pr基合金较高的内禀矫顽力,来源于Pr2Fe14B磁晶各向异性常数比Nd2Fe14B高约30%。加入Pr元素会使合金非晶态的晶化转变温度和转化能降低,热力学稳定性变差,退火时晶粒易于长大,从而使合金的显微组织结构较粗大和较不均匀,降低合金的剩磁。本论文制备了不同Co含量和不同Zr含量的(Nd0.2Pr0.8)10.5Fe82.5-xCoxZr1B6和(Nd0.2Pr0.8)10.5Fe81.5-xCo2ZrxB6系列粘结磁体。添加的Co原子进入硬磁相和软磁相,取代Fe原子位置,使合金的饱和磁化强度提高,内禀矫顽力降低。Co元素添加量为2%的合金,(BH)m和退磁曲线方形度达到最佳。Zr元素通过两个“钉扎”作用来影响合金磁性能。富Zr粒子和晶界处的富Zr相“钉扎”磁性相晶界移动,能非常有效地阻止磁性相的晶粒长大,从而提高合金的Br、Hci和(BH)m。富集于晶界的富Zr相在合金退磁时“钉扎”畴壁,阻碍其移动,从而提高合金的Hci。但是,Zr元素添加过多,富集于晶界的富Zr相体积增加,厚度增大,隔离磁性相晶粒,减弱交换耦合,使合金剩磁下降。1%是合金具有较佳的综合磁性能的最佳Zr元素添加量。本论文通过纳米晶复合永磁合金相组成、各相磁性能及显微组织结构对合金磁性能影响规律的研究,获得了低稀土含量、低Nd元素比例、低Co含量、低Zr含量的(Nd0.2Pr0.8)10.5Fe80.5Co2Zr1B6六元合金。合金的相组成大部分为2:14:1硬磁相,小部分为软磁相α-Fe。合金的平均晶粒尺寸为25nm,且晶粒大小均匀、形状规整。粘结磁体具有良好的综合磁性能:Br=0.662T,Hci=616kA/m,Hcb=410kA/m,(BH)m=74kJ/m3,Hk/Hci=39.9%。合金制备的原材料成本也大幅度降低。这对于更好地综合平衡利用稀土资源,降低永磁材料制备的原材料成本,具有重要的工程意义。更多还原

【Abstract】 According to the summarization and analysis of the exchange coupling principle for nanocrystalline composite permanent magnets and the influence factors of their magnetic properties, several series of iron-based bonded magnets have been prepared by using melt spinning and post annealing method. By means of XRD, AFM, DTA, and TEM, the dependence and mechanism of the preparing process parameters, the rare earths content, the substitution of Nd by Pr, and the addition of Co and Zr on the microstructure of alloy, the intrinsic magnetic feature of magnetic phases, and the magnetic properties of bonded magnets have been systematically investigated.The crystallinity of as-spun alloy significantly influences the microstructure of crystallized ribbons. For the (Nd0.8Pr0.2)10.5Fe77.5Co5Zr1B6, the as-spun alloy ribbons rapidly quenched at 24, 26, 28, and 30 m/s consist of amorphous phases and fine crystallites. The higher the quenching speed is, the lower the alloy crystallinity is, For the as-spun ribbons with the crystallinity of about 30%, which were quenched at 26 m/s, the heterogeneous nucleation of new grains occurs. The nucleation of a <WP=7>solid precipitate from the matrix occurs most easily on boundary already present in the structure and the amount of nuclei is largest. Then a fine and homogenous microstructure and an excellent combination of magnetic properties are obtained. Beyond the 30% of crystallinity, the amount of nuclei decreases and the crystallites present grow easily, which results in an inhomogeneous microstructure. Below 30%, the homogeneous nucleation occurs in the ribbons and the amount of nuclei reduces, which results in an uniform but a coarse grain structure. The annealing temperature and annealing time directly determine the properties of bonded magnets,too. Crystallized at 700℃ for 10 minutes, the magnetic phases precipitate completely and their grains are fine and uniform. The significant interaction among the magnetic grains makes the combination of properties excellent. If annealing temperature<700℃, or time<10min, the magnetic phases precipitate incompletely. If annealing temperature>700℃, or time>10min, the magnetic phases precipitate completely, but the grains grow furthermore. Both of them make the exchange couplings weakened and the magnetic properties degraded.With the decrease of rare earths content for the (Nd0.8Pr0.2)xFe88-xCo5Zr1B6 alloy, the volume fraction of soft magnetic phase and the remanence Br of bonded magnets increase., but both the intrinsic coercivity Hci and the maximum energy product (BH)m decrease. Atom fraction of 10% is the critical rare earths content for the magnetic properties change. Below this value, the magnetic properties, especially Hci, are very low. This experimental result is generally consistent with the calculated result using the model of volume fraction of soft magnetic phase coupled completely. According to this model suggested by us 20% is the maximum volume fraction of soft magnetic phase completely coupled with the hard magnetic phase. Beyond this theoretical value, there may exist some extra soft magnetic phases which are not coupled with the hard magnetic phase. These soft magnetic phases become the nuclei of the reverse magnetic domain and consequently initiate a cascade-type demagnetization process of the assembly.With the increase of Pr content of the (NdxPr1-x)10.5Fe77.5Co5Zr1B6 series alloy, <WP=8>the Hci of bonded magnets increases, but the Br decreases. The (BH)m reaches the maximum value of 70.6 kJ/m3 at x=0.8. For these alloys, the optimum substituted fraction of Nd by Pr is 0.8, in which the best combination of properties is obtained. The higher intrinsic coercivity of Pr-based magnets is derived from the 30% higher anisotropy field of Pr2Fe14B than that of Nd2Fe14B. With the substitution of Nd by Pr the alloy has a lower crystallization temperature and a lower crystallization energy of amorphous, which means that Pr makes the alloy instabler in crystallization kinetics. So the crystallization transition and the grain g更多还原