Transmission electron microscopy study on Nd-rich phase and grain boundary structure of Nd–Fe–B sintered magnets
Transmission electron microscopy study on Nd-rich phase and grain boundary structure of Nd–Fe–B sintered magnets
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DOI：
10.1063/1.1851017
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发表时间：
2005-02
影响因子：
3.2
通讯作者：
Y. Shinba;T. Konno;K. Ishikawa;K. Hiraga;M. Sagawa
中科院分区：
文献类型：
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作者：
Y. Shinba;T. Konno;K. Ishikawa;K. Hiraga;M. Sagawa
用透射电子显微镜（TEM）研究了退火后烧结Nd-Fe-B永磁体中富Nd相的晶体结构和形貌。发现在晶界处厚度小于2nm的富Nd相为非晶态;随着晶界区域的加宽，富Nd相呈现面心立方（fcc）结构，其衍射峰宽为λ 0.54nm;最终，选区衍射图显示出系统允许的超晶格斑点，表明富Nd相属于空间群Ia 3 <$，衍射峰宽为λ 1.1nm。富钕相的元素分析表明，它含有相当数量的氧。这些结果表明，富Nd相（直径约1.1nm）实际上是立方Nd_2O_3（Mn_2O_3结构）的同构相。在Nd_2Fe_（14）B晶粒内部还发现了直径为几十到几百nm的富Nd面心立方相（a = 0.54nm）。晶间和晶内富Nd相与基体Nd 2Fe 14 B相具有简单的取向关系，如（111）Nd 2Fe 14 B →（111）Nd-rich [2 <$].
The crystal structure and morphology of the Nd-rich phase in postannealed sintered Nd–Fe–B hard magnets were investigated by transmission electron microscopy (TEM). The Nd-rich phase at grain boundaries thinner than about 2nm was found to be amorphous; as the boundary region broadened, it assumed a face-centered cubic (fcc) structure with a≈0.54nm; eventually, the selected area diffraction pattern exhibited systematically allowed superlattice spots, revealing that the Nd-rich phase belongs to the space group Ia3¯ with a≈1.1nm. The elemental analysis of the Nd-rich phase showed that it contains a considerable amount of oxygen. These findings indicate that the Nd-rich phase with a≈1.1nm is in fact isostructural to cubic Nd2O3 (Mn2O3 structure). We also found Nd-rich fcc precipitates (a≈0.54nm) of several ten to hundred nm inside the Nd2Fe14B grains. Both intergranular and intragrain Nd-rich phases possess simple orientation relationships with the matrix Nd2Fe14B phase, such as (111)Nd2Fe14B‖(111)Nd‐rich [2¯...