混合稀土的含量对烧结R-Fe-B材料磁性能的影响

发布时间：2018-03-08 01:08

  本文选题：混合稀土　切入点：双合金　出处：《中国科学院大学(中国科学院物理研究所)》2017年博士论文　论文类型：学位论文

【摘要】：由于Nd相对低的丰度和高的价格,使用高丰度和低价格的La、Ce取代Nd-Fe-B中的部分Nd已经成为近几年稀土永磁材料研究的热点之一。混合稀土MM(Mischmetal)是由La、Ce、Pr和Nd按一定比例组成的混合物,是稀土分离过程的中间产物。使用混合稀土取代Nd-Fe-B中的部分Nd,既有利于稀土的平衡和综合利用又可以降低磁体的成本。本文制备并研究了混合稀土铁硼、混合稀土铁硼与钕铁硼的多主相磁体,并对磁体的基本磁性能和显微结构等进行了分析,主要得到以下结论:用电弧熔炼方法制备了MM_(14)Fe_(79.9)B_(6.1)(MM=La_(28.0)Ce_(52.0)Pr_(5.1)Nd_(14.7Sm0.20)合金,XRD精修得到样品的主相为MM_2Fe_(14)B,其晶格常数a=8.780?,c=12.185?,计算出理论密度为ρ=7.589 g/cm3,均小于Nd-Fe-B的值。用传统烧结方法制备了MM_(14)Fe_(79.9)B_(6.1)磁体,得到磁体的居里温度约为210 oC,远小于Nd-Fe-B磁体的居里温度。当烧结温度为1030 oC时,磁体的密度为7.52 g/cm3。经过900oC一级回火后,磁体的矫顽力Hcj和最大磁能积(BH)max都有了一定程度的提升。经过1010 oC烧结和900 oC一级回火后,磁体的性能为Hcj=1.08 kOe和(BH)max=7.72 MGOe。当烧结温度达到1050 oC时,磁体的晶粒显著长大,磁性能急剧降低。通过EDS分析结果表明,La进入了主相晶粒中,但进入主相的La比混合稀土中La的比例少约7.5 at.%,这可能是由于La不容易形成2:14:1相的原因。用双合金法制备了不同成分比例的MM_(14)Fe_(79.9)B_(6.1)/Nd_(13.5)Fe_(80.5)B_6多主相磁体。当烧结温度为1030 oC时,磁体的密度为7.55 g/cm3。当混合稀土MM含量占稀土R总量的值(MM/R)大于30.3 at.%时,磁体具有两个居里温度Tc1和Tc2,其中Tc1对应的是富LaCe主相的居里温度,Tc2对应的是富Nd主相的居里温度。当MM/R从30.3 at.%增加到50.6 at.%,Tc1则由276.5 oC下降到256.6 oC。磁体的Hcj和(BH)max随混合稀土MM的增加而下降,当MM/R=30.3 at.%,磁体的Hcj=7.11 kOe、(BH)max=41.0 MGOe。当MM/R=50.6 at.%时,磁体的Hcj=4.84kOe、(BH)max=34.0 MGOe。随着混合稀土含量的增加,磁体主相晶粒中La、Ce、Pr和Nd分布的不均匀性增加,这种不均匀性使得晶粒内部交换耦合作用增强,有利于提高磁体的剩磁。对于多主相磁体,矫顽力机制为畴壁钉扎机制。通过微磁学模拟Ce2Fe14B/Nd_2Fe_(14)B磁体发现,具有“核壳结构”的磁体具有更高的矫顽力,但并不是“壳”的厚度越厚越好,因为“壳”厚度的增加,会使磁体的不均匀性变差,降低磁体晶粒之间的长程静磁相互作用,进而导致矫顽力的下降。同样用双合金法制备了不同成分比例的MM_(14)Fe_(79.9)B_(6.1)/N45N45的成分大约为(Pr,Nd,Dy)30.5Febal(Al,Cu)0.7B1)多主相磁体。在直接二级回火处理时,磁体的矫顽力随着回火温度的升高而有略微的下降。经过一级回火和二级回火后的磁体的磁性能与直接进行二级回火处理的磁体的性能基本相当。因此,制备混合稀土铁硼与钕铁硼多主相磁体的过程中,可以不用一级回火处理,直接二级回火处理即可。MM/R约为30 at.%磁体的最佳磁性能为Br=13.22 kGs、Hcj=9.55 kOe、(BH)max=40.39 MGOe。
[Abstract]:Because of the abundance of Nd is relatively low and high prices, high abundance and low price La, Ce replace Nd in Nd-Fe-B has become one of the hot spots in recent years, rare earth permanent magnet materials research. Mixed rare earth MM (Mischmetal) is composed of La, Ce, Pr and Nd mixture according to a certain proportion, is the intermediate product of rare earth separation process. The use of mixed rare earth to replace part of the Nd Nd-Fe-B, is conducive to the balanced and comprehensive utilization of rare earth magnet and can reduce the cost. This paper prepared and studied the mixed rare earth iron boron, iron and boron mixed rare earth NdFeB magnets and the main magnetic properties of the magnet, the basic and microstructure were analyzed. The main conclusions are as follows: using arc melting method to prepare MM_ (14) Fe_ (79.9) B_ (6.1) (MM=La_ (28) Ce_ (52) Pr_ (5.1) Nd_ (14.7Sm0.20) alloy, XRD refinement to obtain the sample the main phase is MM_2Fe_ (14) B, the lattice constant of a= 8.780?, c=12.185?, to calculate the density of P =7.589 g/cm3, were less than the value of Nd-Fe-B. With the traditional sintering preparation method of MM_ (14) Fe_ (79.9) B_ (6.1) magnet, magnet can get the Curie temperature is about 210 oC, far less than the Curie temperature of Nd-Fe-B magnet. When the sintering temperature for 1030 oC, the magnet density is 7.52 g/cm3. after 900oC level after tempering, the coercivity of Hcj magnets and the maximum energy product (BH) of Max have a certain degree of improvement. After 1010 oC and 900 oC sintering level after tempering, the magnet performance for Hcj=1.08 kOe and max=7.72 MGOe. (BH) when the sintering temperature reaches 1050 oC, the magnet grains grow up, the magnetic properties decreased sharply. Through the analysis of EDS showed that La entered the main phase grain, but to enter the main phase of La is about 7.5 at.% less than La in rare earth mixture proportion, this may be because the La is not easy to cause the:1 2:14 using the double alloy method. 澶囦簡涓嶅悓鎴愬垎姣斾緥鐨凪M_(14)Fe_(79.9)B_(6.1)/Nd_(13.5)Fe_(80.5)B_6澶氫富鐩哥�佷剑�

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