各向异性HDDR NdFeB磁粉的制备与研究
|
摘要
热处理的六元合金Nd12.8Fe72Co7.8B7Zr0.1Ga0.3铸片制备各向异性磁粉的可能性,并以三元合金Nd13.5Fe79.5B7为例研究了HDDR磁粉各向异性的起源和形成机理。主要研究工作如下：
1.理论研究工作
1)从HDDR磁粉晶粒的特殊微结构出发,研究了HDDR NdFeB永磁合金的反磁化过程和矫顽力机理。结果表明：在lex确定的条件下,当2ro/lex＜1.67时(r0和lex分别为晶粒表面结构缺陷厚度和晶粒间交换耦合长度),决定矫顽力的主要机制是畴壁钉扎；当2ro/lex＞1.67时,决定矫顽力的主要机制是反磁化成核。当2ro/lex=1.67时,矫顽力出现最大值,并与相关的实验结果符合很好。
2)研究了晶粒间界相对磁体矫顽力的影响,改进了晶粒边界的各向异性理论模型。假定晶粒间界相是具有相同厚度的非磁性薄层,且在晶粒间均匀分布,给出了晶粒边界两种不同的各向异性表达式K1'(r)和K1''(r)。结果表明：非磁性晶粒间界相是晶粒之间畴壁位移的钉扎部位。当晶粒间界相厚度d为零时,根据两种表达式计算的矫顽力Hc均相等。d取非零值时,根据两种表达式计算的Hc均随d的增加而上升。其中根据K1''(r)计算的Hc随d的增加而上升的速率快。可是较厚的晶粒间界相又将会导致磁体的磁化强度及剩磁下降很多,限制了磁体磁能积的提高。厚度约为1nm的晶粒间界相可综合提高磁体磁性能。合理地调节合金成分配方及工艺条件,确保磁体中包含少量的富Nd相,不包含α-Fe,可以得到高性能的HDDR NdFeB磁体。当d为1nm, r0约为畴壁厚度(～4nm)时,根据两种表达式计算的矫顽力都与相关的实验结果符合较好。
2.实验研究工作
1)根据实验要求,对原有的实验设备进行了更新、升级和改造。调整并稳定了SC工艺的轮辊转速和石英喷嘴的压力,改造了扩散炉,增加了进气孔,配置了气体压力控制系统。
2)采用SC工艺制备NdFeB合金铸片,研究了SC工艺的辊轮转速对铸片微结构的影响。结果表明：当辊轮转速v=3m／s时制备的铸片呈现最好的微结构。铸片的2：14：1主相被0.05-0.1μm左右的富Nd薄层分割成大约0.5-2μm的片状薄层,主相片状晶组成取向平行的晶粒团簇,富Nd分布均匀,合金中无α-Fe。这样的SC合金铸片经HDDR工艺处理后得到的磁粉晶粒尺寸细小且分布均匀。当轮辊转速过低时,铸片容易出现软磁性相α-Fe,而轮辊转速过高时,贴辊面会出现弥散性分布的非晶,造成钕的偏析,富Nd相分布不再均匀,这都会导致磁粉性能降低。我们确定SC铸片的最佳冷凝速度为3m／s。
3)采用六元合金Nd12.8Fe72Co7.8B7Zr0.1Ga0.3铸片为原料,研究了HDDR工艺过程中的缓慢脱氢再结合氢气压强(简称氢压)对磁粉性能的影响,探讨了直接采用未经均匀化热处理的SC铸片制备各向异性磁粉的可能性。结果表明：磁粉的剩磁Br,矫顽力Hcj,磁能积(BH)max及各向异性取向程度DOA均随氢压的增大先增加后减小。当氢压为30kPa时,磁粉性能均出现极大值,具有明显的各向异性,Br=1.3T, Hcj=954.3kA/m, (BH)max=259 kJ/m3, DOA=0.87。Morimoto等人采用未经均匀化热处理的SC铸片制备的NdFeB磁粉是各向同性的。两者的HDDR工艺区别在于：本文的歧化产物先经缓慢脱氢再结合反应；随后又经过了快速脱氢再结合反应；而Morimoto等人仅将歧化产物经过了快速脱氢再结合反应。歧化产物经缓慢脱氢再结合处理有利于磁粉各向异性的形成。
4)采用三元Nd13.5Fe79.5B7铸片制备了各向异性磁粉,探讨了HDDR磁粉各向异性的产生机理。结果表明：当氢压为20kPa,歧化时间较短(10min)时,DOA=0.76,磁粉具有明显的各向异性。随着歧化时间的延长,DOA逐渐降低。说明磁粉的各向异性可能源于未分解Nd2Fe14B的各向异性,也可能与歧化产物的相成分或微结构相关。歧化产物的XRD谱线分析表明：不同的歧化时间所对应的歧化产物中均包含NdH2、a-Fe和Fe2B相,无任何其它相。说明HDDR磁粉的明显各向异性既不是源于未分解Nd2Fe14B的各向异性,也与歧化产物的相成分无关。歧化产物微结构的SEM分析表明：歧化时间小于10min时,歧化产物的微结构呈现片状晶。随着歧化时间的延长,片状晶逐渐粗化,歧化组织中开始有柱状晶出现。歧化时间进一步延长,歧化产物的微结构完全呈现柱状晶。说明歧化时间较短时,HDDR磁粉所呈现出来的明显各向异性与歧化产物的片状微结构密切相关。这可能是由于片状的歧化产物(中间相产物)保留或继承了原制备态SC合金的硬磁性母相的取向,又与再结合过程中新生成的Nd2Fe14B晶粒的取向有关,从而磁粉呈现各向异性取向。磁粉各向异性的产生机理符合“中间相模型”。
我们的理论研究从HDDR晶粒的特殊微结构出发,建立了晶粒边界的各向异性理论模型,搞清了磁体的反磁化过程和矫顽力机理,为制备高矫顽力磁体提供了重要的理论参考。
我们的实验研究表明：无论是否添加其他元素,直接采用未经热处理的SC合金铸片经优化的HDDR工艺处理都可以制备各向异性NdFeB磁粉。是否含有添加元素及SC铸片是否经均匀化热处理都不是制备各向异性磁粉的必要条件,其关键技术在于HDDR工艺的调节,即适当地加快歧化反应过程,减缓脱氢再结合过程以及控制缓慢脱氢再结合过程的合适氢气压强。我们的研究不仅节省了均匀化热处理的时间和能源,而且为降低成本,制备高性能的各向异性磁粉和磁体提供了参考。
The NdFeB permanent magnetic materials with the greatest properties and developmental future can be divided into the sintered and bonded NdFeB magnets, according to their different preparation processes. Compared with the sintered magnets, the preparation technology of bonded magnets is simple and has low cost, high toughness and performance of resisting the damage and crack. Thus, the bonded magnets can be prepared into products with different shapes. The anisotropic magnetic powders used for producing the bonded magnets are usually prepared by the HDDR(Hydrogenation, Decomposition, Desorption, Recombination)process. By using this process, the original large Nd2Fe14B grains in the cast ingots are transformed into fine grains with diameter of around 0.3μm, which is close to single domain size of Nd2Fe14B phase. The special grain microstructure of HDDR magnets is different from that of both sintered magnets and nanocomposite magnets. Due to the coercivity of magnets closely related to the grain microstructure, so, the coercivity mechanism of HDDR bonded magnets is different from not only that of sintered magnets, but also that of nanocomposite magnets. So far, the coercivity mechanism of HDDR bonded magnets has not been completely clear yet.
The HDDR magnetic powders are commonly prepared from the segregated master ingots, and their magnetic properties are low due to the existence of soft magnetic phaseα-Fe in the master ingots. The alloy flakes prepared by the SC (strip casting) process have a good columnar crystalline structure, the main phase Nd2Fe14B is uniformly separated by the symmetrical Nd-rich phase fine lamella and a-Fe is nonexistent, which is very suitable for preparing the HDDR magnetic powders. Morimoto et al. reported that the HDDR magnetic powders prepared directly from the SC alloy flakes without any heat treatment are isotropic. Subsequently, they prepared the anisotropic magnetic powers by homogenizing SC alloy flakes before the HDDR process. Up to date, the preparation of anisotropic magnetic powers directly from the SC alloy flakes without any heat treatment has still not been reported.
Early experiment results indicated that the addition of elements such as Co, Zr, Nb and Ga is prerequisite for the inducement of anisotropy in the NdFeB-type alloys treated by the HDDR process. The subsequent experiments showed that purely ternary NdFeB anisotropic magnetic powders can also be obtained by using a modified HDDR process treatment. Not only the addition elements, but also the HDDR process plays an important role in the inducement of anisotropy. Because the composition and HDDR process used for preparing anisotropic magnetic powders have not ripened completely, thus, the inducement mechanism of anisotropy of magnetic powders during HDDR process has not been clear completely.
Our research work includes the theoretical and experimental investigation. Theoretically, considering the special microstructure of HDDR magnetic powder grains, we established a theoretical model of anisotropy at the grain boundaries, and investigated the coercivity mechanism of HDDR NdFeB magnets and the effect of intergranular phase on the coercivity of magnets. Experimentally, we prepared the NdFeB magnetic powders by using the SC+HDDR process, probed the possibility of preparing anisotropic magnetic powders directly from hexahydric alloy Nd12.8Fe72Co7.8B7Zr0.1Ga0.3 flakes without any heat treatment, and further clarified the origin of anisotropy of HDDR magnetic powders taking Nd13.5Fe79.5B7 as example. The main contents and important results are following:
1. Theoretical research
1) Considering the special microstructure of HDDR magnetic powder grains, we investigated the demagnetization process and coercivity mechanism in the HDDR NdFeB permanent magnetic alloy. The results indicated that for a fixed lex, when 2ro/lex<1.67 (where r0 and lex are the defect thickness at the grain surface and the length of exchange coupling between grains, respectively), the coercivity is determined by the domain wall pinning mechanism; When 2ro/lex＞1.67, the coercivity is controlled by the demagnetization nucleation mechanism; When 2ro/lex=1.67, the coercivity reaches the maximum, which is consistent well with the correlative experiment results.
2) We investigated the effect of intergranular phase (IP) on the coercivity of magnets based on the optimized theory model of anisotropy at the grain boundaries. Assume that the IP is a nonmagnetic thin layer with the same thickness, and distributes homogeneously between grains. We gave the two different anisotropic expressions K1'(r) and K1"(r) at the grain boundaries. The calculated results indicated that the nonmagnetic intergranular phase is the pinning center of domain wall displacement. When the thickness of intergranular phase d is zero, the calculated coercivity Hc based on K1'(r) are equal to the corresponding ones based on K1'(r). While d takes nonzero values, the calculated Hc based on K1'(r) rises more rapidly as d increases. But the thick IP will markedly decrease the magnetization and remanence of magnets, thus, the enhancement of magnetic energy product will be restricted. The intergranular phase with the thickness of about 1nm can synthetically improve the magnetic performance. As long as one reasonably adjusts the alloy's composition and technical process, to ensure the HDDR magnets containing small amount of Nd-rich phase, and excluding a-Fe, the HDDR NdFeB magnets with high performance could be obtained. When d is 1nm and the structure defect thickness ro is close to the thickness of domain wall (-4 nm), the calculated coercivity based on the two different anisotropic expressions are both consistent well with the interrelated experiment results.
2. Experimental research
1) The experiment equipments were updated and transformed according to the experimental requirement. The wheel speeds and quartz nozzle pressure of SC process were steadied and controlled, respectively, the diffusion furnace was transformed, the air inlets were increased, and the aero-pressure control system was deployed.
2) The NdFeB alloy flakes were prepared by using the SC process, and the effects of wheel speeds of SC process on the microstructure of alloy flakes were investigated. The results indicated that the alloy flakes prepared with wheel speed of 3m/s display the optimal microstructure. The flakes contain the main phase Nd2Fe14B phase lamellae with a width ranging from 0.5 to 2μm separated by about 0.05 to 0.1μm wide Nd-rich phases. The main phase lamella crystals show parallel orientation. The Nd-rich phase is distributed uniformly and a-Fe isn't present. Such SC alloy flake subjected to the HDDR process can obtain the fine powder grains with a uniform dimension distribution. If the wheel speeds are slower than 3m/s, the free surface of SC alloy flake displays a-Fe dendrites. However, if the wheel speeds are higher than 3m/s, there is a pool region of Nd-rich phases near the cooling surface, which leads to the segregation of the Nd-rich phase. Both higher and lower cooling speeds will all lead to the reduction of magnetic performance of powders. Thus, the wheel speed of 3m/s is considered the optimized cooling speed.
3) Using the hexahydric alloy flakes with the composition of Nd12.8Fe72Co7.8gB7Zr0.1Ga0.3, we investigated the effect of hydrogen pressure of slow recombination treatment (HPSR) on the magnetic performances of powders, and probed the possibility of preparing anisotropic magnetic powders directly from the SC alloy flakes without any heat treatment. The results indicated that the remanence Br, coercivity Hcj, magnetic energy product (BH)max and degree of orientation of anisotropy (DOA) all increase firstly, and then decrease with increasing HPSR. While the HPSR is 30kPa, the magnetic powders are obviously anisotropic, and the magnetic performances achieve the maximum values of Br=1.3T, Hcj=954.3kA/m, (BH)max=259 kJ/m3 and DOA=0.87, respectively. Morimoto et al. reported that the HDDR magnetic powders prepared directly from the SC alloy flakes without any heat treatment are isotropic. The difference between two processes is that in the recombination stage during the HDDR process, the disproportionated products are firstly carried out a slow desorption-recombination reaction in low hydrogen pressure before they are carried out a fast desorption-recombination reaction in high vacuum in our paper, however, the disproportionated products are directly subjected to a fast desorption-recombination reaction in high vacuum in Morimoto's paper. That the disproportionated products subjected to a slow desorption-recombination reaction in the low hydrogen pressure is favorable to the inducement of anisotropy of magnetic powders.
4) The inducement mechanism of anisotropy of HDDR magnetic powders prepared by using the ternary Nd13.5Fe79.5B7 alloy flakes were probed. The results indicated that for the HPSR of 20kPa, when the disproportionation time is 10min, DOA=0.76, the magnetic powders are evidently anisotropic. With prolonging disproportionation time, DOA gradually decreases. It is indicated that the anisotropy of magnetic powders may be derive from the anisotropy of undecomposed Nd2Fe14B phase, and may also be related to the phase composition and microstructure of disproportionated products. The XRD patterns of disproportionated products indicated that no other phases except NdH2、α-Fe and Fe2B are found in the disproportionation products corresponding to different disproportionation time. Thus, the evident anisotropy of magnetic powders corresponding to a short disproportionation time does not derive from the anisotropy of undecomposed Nd2Fe14B phase, and is also unrelated to the phase composition of disproportionated products. SEM observation of microstructures of disproportionation products showed that when the disproportionation time is short (10min), the microstructure of disproportionated products is characteristic of the lamella crystal. With longer disproportionation time, some of the initial lamella crystal gradually coarsens, and the columnar crystal begins to appear. When the disproportionation time further increases, the lamella crystal completely disappears, and transforms into the columnar crystal. This illustrates that the obvious anisotropy of the magnetic powders corresponding to a short disproportionation time originates from the lamella disproportionated mixture. This may be attributed to that the lamella disproportionated mixture (intermediate phase) remains or inherits the alignment of hard magnetic phase of original SC alloys, and may also be related to the alignment of the newly formed Nd2Fe14B grain, which results in the magnetic powders displaying the evidently anisotropic alignment. The generating mechanism of anisotropy is in accordance with "anisotropy-mediating phase" model.
Theoretically, the model of anisotropy at the grain boundaries of HDDR NdFeB magnets was established based on the special microstructure of HDDR grains, and the demagnetization process and coercivity mechanism of magnets were understood, which will provide an importantly theoretical reference for preparing the magnets with high coercivity.
Our experimental investigation indicated that whether or not adds the element, the anisotropic NdFeB magnetic powders can be obtained by using the SC alloy flake without any heat treatment subjected to an modified HDDR process treatment. Whether the element added and SC flakes subjected to the homogenization heat treatment or not are not necessary for obtaining the anisotropic magnetic powders. The key to the adjustment of HDDR process, i.e., appropriately speed disproportionation reaction course, slow desorption-recombination reaction course, and control the appropriate hydrogen pressure during the slow recombination stage. Our research avoids the homogenizing heat treatment which expends long time and huge amounts of energy, so, it will provide an important reference for reducing cost and preparing highly anisotropic magnetic powders and bonded magnets.
1.理论研究工作
1)从HDDR磁粉晶粒的特殊微结构出发,研究了HDDR NdFeB永磁合金的反磁化过程和矫顽力机理。结果表明：在lex确定的条件下,当2ro/lex＜1.67时(r0和lex分别为晶粒表面结构缺陷厚度和晶粒间交换耦合长度),决定矫顽力的主要机制是畴壁钉扎；当2ro/lex＞1.67时,决定矫顽力的主要机制是反磁化成核。当2ro/lex=1.67时,矫顽力出现最大值,并与相关的实验结果符合很好。
2)研究了晶粒间界相对磁体矫顽力的影响,改进了晶粒边界的各向异性理论模型。假定晶粒间界相是具有相同厚度的非磁性薄层,且在晶粒间均匀分布,给出了晶粒边界两种不同的各向异性表达式K1'(r)和K1''(r)。结果表明：非磁性晶粒间界相是晶粒之间畴壁位移的钉扎部位。当晶粒间界相厚度d为零时,根据两种表达式计算的矫顽力Hc均相等。d取非零值时,根据两种表达式计算的Hc均随d的增加而上升。其中根据K1''(r)计算的Hc随d的增加而上升的速率快。可是较厚的晶粒间界相又将会导致磁体的磁化强度及剩磁下降很多,限制了磁体磁能积的提高。厚度约为1nm的晶粒间界相可综合提高磁体磁性能。合理地调节合金成分配方及工艺条件,确保磁体中包含少量的富Nd相,不包含α-Fe,可以得到高性能的HDDR NdFeB磁体。当d为1nm, r0约为畴壁厚度(～4nm)时,根据两种表达式计算的矫顽力都与相关的实验结果符合较好。
2.实验研究工作
1)根据实验要求,对原有的实验设备进行了更新、升级和改造。调整并稳定了SC工艺的轮辊转速和石英喷嘴的压力,改造了扩散炉,增加了进气孔,配置了气体压力控制系统。
2)采用SC工艺制备NdFeB合金铸片,研究了SC工艺的辊轮转速对铸片微结构的影响。结果表明：当辊轮转速v=3m／s时制备的铸片呈现最好的微结构。铸片的2：14：1主相被0.05-0.1μm左右的富Nd薄层分割成大约0.5-2μm的片状薄层,主相片状晶组成取向平行的晶粒团簇,富Nd分布均匀,合金中无α-Fe。这样的SC合金铸片经HDDR工艺处理后得到的磁粉晶粒尺寸细小且分布均匀。当轮辊转速过低时,铸片容易出现软磁性相α-Fe,而轮辊转速过高时,贴辊面会出现弥散性分布的非晶,造成钕的偏析,富Nd相分布不再均匀,这都会导致磁粉性能降低。我们确定SC铸片的最佳冷凝速度为3m／s。
3)采用六元合金Nd12.8Fe72Co7.8B7Zr0.1Ga0.3铸片为原料,研究了HDDR工艺过程中的缓慢脱氢再结合氢气压强(简称氢压)对磁粉性能的影响,探讨了直接采用未经均匀化热处理的SC铸片制备各向异性磁粉的可能性。结果表明：磁粉的剩磁Br,矫顽力Hcj,磁能积(BH)max及各向异性取向程度DOA均随氢压的增大先增加后减小。当氢压为30kPa时,磁粉性能均出现极大值,具有明显的各向异性,Br=1.3T, Hcj=954.3kA/m, (BH)max=259 kJ/m3, DOA=0.87。Morimoto等人采用未经均匀化热处理的SC铸片制备的NdFeB磁粉是各向同性的。两者的HDDR工艺区别在于：本文的歧化产物先经缓慢脱氢再结合反应；随后又经过了快速脱氢再结合反应；而Morimoto等人仅将歧化产物经过了快速脱氢再结合反应。歧化产物经缓慢脱氢再结合处理有利于磁粉各向异性的形成。
4)采用三元Nd13.5Fe79.5B7铸片制备了各向异性磁粉,探讨了HDDR磁粉各向异性的产生机理。结果表明：当氢压为20kPa,歧化时间较短(10min)时,DOA=0.76,磁粉具有明显的各向异性。随着歧化时间的延长,DOA逐渐降低。说明磁粉的各向异性可能源于未分解Nd2Fe14B的各向异性,也可能与歧化产物的相成分或微结构相关。歧化产物的XRD谱线分析表明：不同的歧化时间所对应的歧化产物中均包含NdH2、a-Fe和Fe2B相,无任何其它相。说明HDDR磁粉的明显各向异性既不是源于未分解Nd2Fe14B的各向异性,也与歧化产物的相成分无关。歧化产物微结构的SEM分析表明：歧化时间小于10min时,歧化产物的微结构呈现片状晶。随着歧化时间的延长,片状晶逐渐粗化,歧化组织中开始有柱状晶出现。歧化时间进一步延长,歧化产物的微结构完全呈现柱状晶。说明歧化时间较短时,HDDR磁粉所呈现出来的明显各向异性与歧化产物的片状微结构密切相关。这可能是由于片状的歧化产物(中间相产物)保留或继承了原制备态SC合金的硬磁性母相的取向,又与再结合过程中新生成的Nd2Fe14B晶粒的取向有关,从而磁粉呈现各向异性取向。磁粉各向异性的产生机理符合“中间相模型”。
我们的理论研究从HDDR晶粒的特殊微结构出发,建立了晶粒边界的各向异性理论模型,搞清了磁体的反磁化过程和矫顽力机理,为制备高矫顽力磁体提供了重要的理论参考。
我们的实验研究表明：无论是否添加其他元素,直接采用未经热处理的SC合金铸片经优化的HDDR工艺处理都可以制备各向异性NdFeB磁粉。是否含有添加元素及SC铸片是否经均匀化热处理都不是制备各向异性磁粉的必要条件,其关键技术在于HDDR工艺的调节,即适当地加快歧化反应过程,减缓脱氢再结合过程以及控制缓慢脱氢再结合过程的合适氢气压强。我们的研究不仅节省了均匀化热处理的时间和能源,而且为降低成本,制备高性能的各向异性磁粉和磁体提供了参考。
The NdFeB permanent magnetic materials with the greatest properties and developmental future can be divided into the sintered and bonded NdFeB magnets, according to their different preparation processes. Compared with the sintered magnets, the preparation technology of bonded magnets is simple and has low cost, high toughness and performance of resisting the damage and crack. Thus, the bonded magnets can be prepared into products with different shapes. The anisotropic magnetic powders used for producing the bonded magnets are usually prepared by the HDDR(Hydrogenation, Decomposition, Desorption, Recombination)process. By using this process, the original large Nd2Fe14B grains in the cast ingots are transformed into fine grains with diameter of around 0.3μm, which is close to single domain size of Nd2Fe14B phase. The special grain microstructure of HDDR magnets is different from that of both sintered magnets and nanocomposite magnets. Due to the coercivity of magnets closely related to the grain microstructure, so, the coercivity mechanism of HDDR bonded magnets is different from not only that of sintered magnets, but also that of nanocomposite magnets. So far, the coercivity mechanism of HDDR bonded magnets has not been completely clear yet.
The HDDR magnetic powders are commonly prepared from the segregated master ingots, and their magnetic properties are low due to the existence of soft magnetic phaseα-Fe in the master ingots. The alloy flakes prepared by the SC (strip casting) process have a good columnar crystalline structure, the main phase Nd2Fe14B is uniformly separated by the symmetrical Nd-rich phase fine lamella and a-Fe is nonexistent, which is very suitable for preparing the HDDR magnetic powders. Morimoto et al. reported that the HDDR magnetic powders prepared directly from the SC alloy flakes without any heat treatment are isotropic. Subsequently, they prepared the anisotropic magnetic powers by homogenizing SC alloy flakes before the HDDR process. Up to date, the preparation of anisotropic magnetic powers directly from the SC alloy flakes without any heat treatment has still not been reported.
Early experiment results indicated that the addition of elements such as Co, Zr, Nb and Ga is prerequisite for the inducement of anisotropy in the NdFeB-type alloys treated by the HDDR process. The subsequent experiments showed that purely ternary NdFeB anisotropic magnetic powders can also be obtained by using a modified HDDR process treatment. Not only the addition elements, but also the HDDR process plays an important role in the inducement of anisotropy. Because the composition and HDDR process used for preparing anisotropic magnetic powders have not ripened completely, thus, the inducement mechanism of anisotropy of magnetic powders during HDDR process has not been clear completely.
Our research work includes the theoretical and experimental investigation. Theoretically, considering the special microstructure of HDDR magnetic powder grains, we established a theoretical model of anisotropy at the grain boundaries, and investigated the coercivity mechanism of HDDR NdFeB magnets and the effect of intergranular phase on the coercivity of magnets. Experimentally, we prepared the NdFeB magnetic powders by using the SC+HDDR process, probed the possibility of preparing anisotropic magnetic powders directly from hexahydric alloy Nd12.8Fe72Co7.8B7Zr0.1Ga0.3 flakes without any heat treatment, and further clarified the origin of anisotropy of HDDR magnetic powders taking Nd13.5Fe79.5B7 as example. The main contents and important results are following:
1. Theoretical research
1) Considering the special microstructure of HDDR magnetic powder grains, we investigated the demagnetization process and coercivity mechanism in the HDDR NdFeB permanent magnetic alloy. The results indicated that for a fixed lex, when 2ro/lex<1.67 (where r0 and lex are the defect thickness at the grain surface and the length of exchange coupling between grains, respectively), the coercivity is determined by the domain wall pinning mechanism; When 2ro/lex＞1.67, the coercivity is controlled by the demagnetization nucleation mechanism; When 2ro/lex=1.67, the coercivity reaches the maximum, which is consistent well with the correlative experiment results.
2) We investigated the effect of intergranular phase (IP) on the coercivity of magnets based on the optimized theory model of anisotropy at the grain boundaries. Assume that the IP is a nonmagnetic thin layer with the same thickness, and distributes homogeneously between grains. We gave the two different anisotropic expressions K1'(r) and K1"(r) at the grain boundaries. The calculated results indicated that the nonmagnetic intergranular phase is the pinning center of domain wall displacement. When the thickness of intergranular phase d is zero, the calculated coercivity Hc based on K1'(r) are equal to the corresponding ones based on K1'(r). While d takes nonzero values, the calculated Hc based on K1'(r) rises more rapidly as d increases. But the thick IP will markedly decrease the magnetization and remanence of magnets, thus, the enhancement of magnetic energy product will be restricted. The intergranular phase with the thickness of about 1nm can synthetically improve the magnetic performance. As long as one reasonably adjusts the alloy's composition and technical process, to ensure the HDDR magnets containing small amount of Nd-rich phase, and excluding a-Fe, the HDDR NdFeB magnets with high performance could be obtained. When d is 1nm and the structure defect thickness ro is close to the thickness of domain wall (-4 nm), the calculated coercivity based on the two different anisotropic expressions are both consistent well with the interrelated experiment results.
2. Experimental research
1) The experiment equipments were updated and transformed according to the experimental requirement. The wheel speeds and quartz nozzle pressure of SC process were steadied and controlled, respectively, the diffusion furnace was transformed, the air inlets were increased, and the aero-pressure control system was deployed.
2) The NdFeB alloy flakes were prepared by using the SC process, and the effects of wheel speeds of SC process on the microstructure of alloy flakes were investigated. The results indicated that the alloy flakes prepared with wheel speed of 3m/s display the optimal microstructure. The flakes contain the main phase Nd2Fe14B phase lamellae with a width ranging from 0.5 to 2μm separated by about 0.05 to 0.1μm wide Nd-rich phases. The main phase lamella crystals show parallel orientation. The Nd-rich phase is distributed uniformly and a-Fe isn't present. Such SC alloy flake subjected to the HDDR process can obtain the fine powder grains with a uniform dimension distribution. If the wheel speeds are slower than 3m/s, the free surface of SC alloy flake displays a-Fe dendrites. However, if the wheel speeds are higher than 3m/s, there is a pool region of Nd-rich phases near the cooling surface, which leads to the segregation of the Nd-rich phase. Both higher and lower cooling speeds will all lead to the reduction of magnetic performance of powders. Thus, the wheel speed of 3m/s is considered the optimized cooling speed.
3) Using the hexahydric alloy flakes with the composition of Nd12.8Fe72Co7.8gB7Zr0.1Ga0.3, we investigated the effect of hydrogen pressure of slow recombination treatment (HPSR) on the magnetic performances of powders, and probed the possibility of preparing anisotropic magnetic powders directly from the SC alloy flakes without any heat treatment. The results indicated that the remanence Br, coercivity Hcj, magnetic energy product (BH)max and degree of orientation of anisotropy (DOA) all increase firstly, and then decrease with increasing HPSR. While the HPSR is 30kPa, the magnetic powders are obviously anisotropic, and the magnetic performances achieve the maximum values of Br=1.3T, Hcj=954.3kA/m, (BH)max=259 kJ/m3 and DOA=0.87, respectively. Morimoto et al. reported that the HDDR magnetic powders prepared directly from the SC alloy flakes without any heat treatment are isotropic. The difference between two processes is that in the recombination stage during the HDDR process, the disproportionated products are firstly carried out a slow desorption-recombination reaction in low hydrogen pressure before they are carried out a fast desorption-recombination reaction in high vacuum in our paper, however, the disproportionated products are directly subjected to a fast desorption-recombination reaction in high vacuum in Morimoto's paper. That the disproportionated products subjected to a slow desorption-recombination reaction in the low hydrogen pressure is favorable to the inducement of anisotropy of magnetic powders.
4) The inducement mechanism of anisotropy of HDDR magnetic powders prepared by using the ternary Nd13.5Fe79.5B7 alloy flakes were probed. The results indicated that for the HPSR of 20kPa, when the disproportionation time is 10min, DOA=0.76, the magnetic powders are evidently anisotropic. With prolonging disproportionation time, DOA gradually decreases. It is indicated that the anisotropy of magnetic powders may be derive from the anisotropy of undecomposed Nd2Fe14B phase, and may also be related to the phase composition and microstructure of disproportionated products. The XRD patterns of disproportionated products indicated that no other phases except NdH2、α-Fe and Fe2B are found in the disproportionation products corresponding to different disproportionation time. Thus, the evident anisotropy of magnetic powders corresponding to a short disproportionation time does not derive from the anisotropy of undecomposed Nd2Fe14B phase, and is also unrelated to the phase composition of disproportionated products. SEM observation of microstructures of disproportionation products showed that when the disproportionation time is short (10min), the microstructure of disproportionated products is characteristic of the lamella crystal. With longer disproportionation time, some of the initial lamella crystal gradually coarsens, and the columnar crystal begins to appear. When the disproportionation time further increases, the lamella crystal completely disappears, and transforms into the columnar crystal. This illustrates that the obvious anisotropy of the magnetic powders corresponding to a short disproportionation time originates from the lamella disproportionated mixture. This may be attributed to that the lamella disproportionated mixture (intermediate phase) remains or inherits the alignment of hard magnetic phase of original SC alloys, and may also be related to the alignment of the newly formed Nd2Fe14B grain, which results in the magnetic powders displaying the evidently anisotropic alignment. The generating mechanism of anisotropy is in accordance with "anisotropy-mediating phase" model.
Theoretically, the model of anisotropy at the grain boundaries of HDDR NdFeB magnets was established based on the special microstructure of HDDR grains, and the demagnetization process and coercivity mechanism of magnets were understood, which will provide an importantly theoretical reference for preparing the magnets with high coercivity.
Our experimental investigation indicated that whether or not adds the element, the anisotropic NdFeB magnetic powders can be obtained by using the SC alloy flake without any heat treatment subjected to an modified HDDR process treatment. Whether the element added and SC flakes subjected to the homogenization heat treatment or not are not necessary for obtaining the anisotropic magnetic powders. The key to the adjustment of HDDR process, i.e., appropriately speed disproportionation reaction course, slow desorption-recombination reaction course, and control the appropriate hydrogen pressure during the slow recombination stage. Our research avoids the homogenizing heat treatment which expends long time and huge amounts of energy, so, it will provide an important reference for reducing cost and preparing highly anisotropic magnetic powders and bonded magnets.
引文
[1]R. Coehoorn, D. B. De. Mooij, C. De. Waard. Meltspun permanent magnet materials containing Fe3B as the main phase [J]. J. Magn. Magn. Mater.,1989, 80:101-104.
[2]周寿增,董清飞.超强永磁体[M].北京：冶金工艺出版社,1999.p321.
[3]李强,周邦新.快淬NdFeB粉末的TEM样品制备[J].稀有金属材料与工程.,2004,29(4)：283-284.
[4]R. K. Mishra. Microstructure of melt-spun Nd-Fe-B m agneqench magnets [J]. J. Magn. Magn. Mater.,1986,450:54-57.
[5]M. K. Veistinen, E. J. Lavemia, J. C. Baram, N. J. Grant. Flow mechanisms affecting rapid solidification in high pressure gas atomization [J]. Int. J. Powder Metall.,1989,25:89-92.
[6]丘光汉.气体喷雾-水淬工艺制造Al-Si合金粉末[J].中南工业大学学报.,1995,26：484-487.
[7]L. Schultz, J. Wecker, E. Hellstern. Formation and properties of NdFeB prepared by mechanical alloying and solid-state reaction [J]. J. Appl. Phys.,1987, 61:3583-3585.
[8]T. Takeshita. R. Nakayama. Magnetic properties and microstructure of the NdFeB magnet powder produced by hydrogen treatment, in Proc.10th Int. Workshop on Rare-Earth Magnets and Their Applications. Kyoto, Japan,1989, 551-557.
[9]P. J. McGuiness, X. J. Zhang, H. Forsyth, I. R. Harris. Disproportionation in Nd16Fe76B8-type hydrides [J]. J. Less-Comm. Metals.,1990,162:379-387.
[10]高建荣,宋晓平,王笑天.NdFeB合金HDDR工艺的回顾与展望[J].功能材料.,1995,26(5)：395-397.
[11]Y. Kawashita, N. Waki, T. Tayu, T. Sugiyama, H. Ono, H. Koyama, H. Kanno, T. Uchida. Microstructures and magnetic properties of hydrogenation disproportionation desorption recombination-processed Nd-Fe-B materials with different Nd content of 11.0 and 12.6 at.%[J]. J. Alloys. Compd.,2003,
360:322-329.
[12]D. Book, I. R. Harris.The disproportionation of Nd2Fe14B under hydrogen in Nd-Fe-B alloys [J]. IEEE. Trans. Magn.,1992,28:2145-2147.
[13]M. Matsuura, A. Ashfaq, M. Sakurai, T. Tomida, N. Sano, S. Hirosawa. Ga site occupancy in HDDR-treated Nd2Fe14B based alloy by XAFS [J]. J. Alloys. Compd.,1999,293-295:872-876.
[14]R. Nakayama, T. Takeshita, M. Itakura, N. Kuwano, K. Oki. Magnetic properties and microstructures of the Nd-Fe-B magnet powder produced by hydrogen treatment [J]. J. Appl. Phys.,1991,70:3770-3774.
[15]H. Nakamura, S. Sugimoto, T. Tanaka, M. Okada. M. Homma. Effects of additional elements on hydrogen absorption and desorption characteristics of Sm2Fe17 compounds [J]. J Alloys. Compd.,1995, 222:13-17.
[16]H. Nakamura, S. Sugimoto, M. Okada, M. Homma. High-coercivity Sm2Fe17Nx powders produced by HDDR and nitriding processes [J]. Mater. Chem. Phys., 1992,32:280-285.
[17]O. Gutfleisch, B. Gebel, N. Mattern. Texture in a ternary Nd16.2Fe78.2B5.6 powder using a modified hydrogenation-disproportionation-desorption-recombination process [J]. J. Magn. Magn. Mater.,2000,210:5-9.
[18]H. Nakamura, K. Kato, D. Book. S. Sugimoto, M. Homma. Enhancement of coercivity in high remanence HDDR Nd-Fe-B powders [J]. IEEE. Trans. Magn., 1999,35:3274-3276.
[19]S. Sugimoto, N. Koike, D. Book, T. Kagotani, M. Okada, K. Inomata, M. Homma. An improved HDDR treatment for the production of anisotropic Nd-Fe-B ternary powders [J]. J. Alloys. Compd.,2002,330-332:892-896.
[20]刘旭波.博士论文.北京科技大学,2000,p58-59.
[21]K. Morimoto, E. Niizuma, R. Nakayama, K. Igarashi. Influence of original alloy microstructure on magnetic properties of isotropic HDDR-treated Nd-Fe-B powder [J]. J. Magn. Magn. Mater.,2003,263:201-207.
[22]K. Morimoto, K. Kato, K. Igarashi, R. Nakayama. Magnetic properties of anisotropic Nd-Fe-B HDDR powders prepared from strip cast alloys [J]. J Alloys. Compd.,2004,366:274-278.
[23]G. Shi, L. X. Hu, E. D. Wang. Preparation, microstructure and magnetic properties of a nanocrystalline Nd12Fe82B6 alloy by HDDR combined with mechanical milling [J]. J. Magn. Magn. Mater.,2006,301:319-324.
[24]P. J. McGuiness, X. J. Zhang, X. J. Yin, I. R. Harris. Hydrogenation, disproportionation and desorption (HDD):An effective processing route for Nd-Fe-B-type magnets [J]. J. Less. Common. Metals.,1990,158:359-364.
[25]韩景智,孙爱芝,刘涛,肖耀福,王润.HDDR三元NdFeB各向异性材料的制备[J].北京科技大学学报.,2002,24(2)：137-140.
[26]Y. Kawashita, N. Waki, T. Tayu, T. Sugiyama, H. Ono, H. Koyama, H. Kanno, T. Uchida. Magnetic properties of Nd-Fe-B system anisotropic HDDR powder made from segregated master ingots [J]. J. Magn. Magn. Mater.,2004,269: 293-301.
[27]廖达前,连发增,王继杰,付猛,陈玉兰.HDDR工艺条件及均匀化处理对Nd12.6Fe69.3CO11.6B6.0Al0.5合金磁性能的影响[J].功能材料.,2005,36：190-192.
[28]J. R. Gao, X. P. Song, X. T. Wang. Effects of reduced hydrogen pressure on magnetic properties of HDDR-treated NdFeGaB alloy powders [J]. J Alloys. Compd.,1998,267:270-273.
[29]O. Gutfleisch, G. Drazic, C. Mishima, Y. Honkura Texture inducement during HDDR processing of NdFeB [J]. IEEE.Trans. Magn.,2002,38:2958-2960.
[30]O. Gutfleisch, M. Matzinger, J. Fidler, I. R. Harris. Characterisation of solid-HDDR processed Nd16Fe76B8 alloys by means of electron microscopy [J]. J. Magn. Magn. Mater.,1995,147:320-330.
[31]T. Takashita, K. Morimoto. Anisotropic Nd-Fe-B bonded magnets made from HDDR powders [J]. J. Appl. Phys.,1996,79:5040-5044.
[32]T. Takeshita, R. Nakayama. Magnetic properties and microstructures of the Nd-Fe-B magnet powders produced by the hydrogen treatment-(Ⅲ), in Proc.
11th Int. Workshop on Rare-Earth Magnets and Their Applications. Pittsburgh, America,1990,49-71.
[33]R. Nakayama, T. Takeshita. Nd-Fe-B anisotropic magnet powders produced by the HDDR process [J]. J. Alloys Compd.,1993,193:259-261.
[34]R. Nakayama, T. Takeshita, M. Itakura, N. Kuwano, K. Oki. Microstructures and crystallographic orientation of crystalline grains in anisotropic Nd-Fe-Co-B-(Ga or Zr) magnet powders produced by the hydrogenation-decomposition-desorption-recombination process [J]. J. Appl. Phys.,1994,76(1):412-417.
[35]S. Hirosawa, M. Uehara, S. Mino, N. Ishigaki, T. Tomida. New aspects of Nd-Fe-B-based hydrogenation-disproportionationdesorption-recombination powders and anisotropic bonded magnets made from them:Microstructure and magnetic properties [J]. J. Appl. Phys.,1997,81(8):4821-4826.
[36]S. Sugimoto, H. Nakamura, K. Kato, D. Book, T. Kagotani, M. Okada, M. Homma. Effect of the disproportionation and recombination stages of the HDDR process on the inducement of anisotropy in Nd-Fe-B magnets [J]. J. Alloys Compd.,1999,293-295:862-867.
[37]O. Gutfleisch, B. Gebel, M. Kubis, K. H. Muller, L. Schultz. Modified HDDR procedures applied to NdFeB alloys [J]. IEEE. Trans. Magn.,1999,35:3250-3252.
[38]K. Morimoto, R. Nakayama, K. Mori, K. Igarashi, Y. Ishii, M. Itakura, N. Kuwano, K. Oki. Anisotropic NdFeB-based magnet powder with high remanence produced by modified HDDR process [J]. IEEE. Trans. Magn.1999, 35:3253-3255.
[39]C. Mishima, N. Hamada, H. Mitarai, Y. Honkura. Development of a Co-free NdFeB anisotropic bonded magnet produced from the d-HDDR processed powder [J]. IEEE. Trans. Magn.2001,37:2467-2470.
[40]O. Gutfleisch, K. Khlopkov, A. Teresiak, K. H. Muller, G. Drazic, C. Mishima, Y. Honkura. Memory of Texture During HDDR Processing of NdFeB [J]. IEEE. Trans. Magn.2003,39:2926-2931.
[41]C. Mishima, N. Hamada, H. Mitarai, Y. Honkura. Magnetic properties of NdFeB anisotropic magnet powder produced by the d-HDDR method, in Proc. 16th Int. Workshop on Rare-Earth Magnets and Their Applications. Sendai, Japan,2000,873-880.
[42]T. Tomida, N. Sano, M. Uehara. Orientational memory site in hydrogenation disproportionation desorptionrecombination process of anisotropic Nd2Fe14B-based magnets [J]. J. Appl. Phys.,1997,81(11):7170-7174
[43]I. R. Harris. The use of hydrogen in the production of Nd-Fe-B-type magnets and in the assessment of Nd-Fe-B-type alloys and permanent magnets-An update, in Proc.12th Int. Workshop on Rare-Earth Magnets and Their Applications. Canberra, Australia,1992,347-371.
[44]K. H. J. Bushow. Trends in rare earth permanent magnets [J]. IEEE.Tran. Magn., 1994,30:565-568.
[45]H. Nakamura, R. Suefuji, S. Sugimoto, M. Okada, M. Homma. Effects of HDDR treatment conditions on magnetic properties of Nd-Fe-B anisotropic powders [J]. J. Appl. Phys.,1994,76 (10):6828-6830.
[46]G. Yi, J. N. Chapman, D. N. Brown, I. R. Harris. Intermediate phasesin the hydrogen disproportionated state of NdFeB-type powders [J]. J. Appl. Phys., 2001,90:1924-1930.
[47]T. Tomida, N. Sano, K. Hanafusa, H.Tomizawa, S. Hirosawa. Intermediate hydrogenation phase in the hydrogenation-disproportionation-recombination process of Nd2Fe14B-based anisotropic magnets [J]. Acta. Mater.,1999, 47(3):875-885.
[48]O. Gutfleisch, A. Teresiak, B. Gebel, K. H. Muller, N. B. Cannesan, D. Brown, I. R. Harris. Metastable borides and the inducement of texture in Pr2Fe14B-type magnets produced by HDDR [J]. IEEE. Trans. Magn.,2001,37(4):2471-2473.
[49]J. Z. Han, C. L. Tong, A. Z. Sun, Y. F. Xiao, R. Wang. Microstructural changes during the disproportionation of Nd13Fe80B7 alloys [J]. J. Magn. Magn. Mater., 2004,270:136-141.
[50]R. Nakayama, T. Mugginess. Grain-size dependence of remanence and coercive field of isotropic nanocrystalline composite permanent magnets [J]. J. Magn. Magn. Mater.,1996,153:35-49.
[51]岳明,刘旭波,肖耀福,张久兴.HDDR各向异性NdFeB矫顽力机理的研究[J].稀有金属材料与工程.,2003,32(7)：490-493.
[52]R. W. Gao, J. C. Zhang, D. H. Zhang, Y. Y. Dai, X. H. Meng, Z. M. Wang, Y. J. Zhang, H. Q. Liu. Dependence of the magnetic properties on the alignment magnetic field for NdFeB bonded magnets made from anisotropic HDDR powders [J]. J. Magn. Magn. Mater.,1999,191:97-100.
[1]O. Gutfleisch, G. Drazic, C. Mishima, Y. Honkura. Texture inducement during HDDR processing of NdFeB [J]. IEEE. Trans. Magn.,2002,38:2958-2960.
[2]T. Takeshita, R. Nakayama. Nd-Fe-B anisotropic magnet powders by the HDDR process, in Proc.12th Int. Workshop on Rare-Earth Magnets and Their Applications. Canberra, Australia,1992,259-261.
[3]R. Nakayama, T. Takeshita. M. Itakura, N. Kuwano, K. Oki. Magnetic properties and microstructures of the Nd-Fe-B magnet powder produced by hydrogen treatment [J]. J. Appl. Phys.,1990,67(9):4665-4665.
[4]S. Sugimoto, O. Gutfleisch, I. R. Harris. Resistivity measurements on hydrogenation disproportionation desorption recombination phenomena in Nd-Fe-B alloys with Co, Ga and Zr additions [J]. J. Alloys. Compd.,1997, 260:284-291.
[5]S. B. Rybalka, E.V. Dodonova, V. A. Didus. Some kinetic and microstructural aspects during FeB alloys hydrogen-induced phase transformations in Nd2Fe14B alloys [J]. J. Alloys. Compd.,2005,404-406:588-594.
[6]K. Morimoto, K. Igarashi, K. Kato, R. Nakayama, M.Yagi. Anisotropic HDDR-treated Nd-Fe-B alloy flakes for mechanically oriented composite magnets [J]. J. Alloys. Compd.,2005,393:311-315.
[7]W. Chen, R. W. Gao, M.G. Zhu, W. Pan, W. Li, X. M. Li, G. B. Han, W.C. Feng, B. Wang. Magnetic properties and coercivity mechanism of isotropic HDDR NdFeB bonded magnets with Co and Dy addition [J]. J. Magn. Magn. Mater., 2003,261:222-227.
[8]R. Nakayama, T. Takeshita, M. Itakura, N. Kuwano, K. Oki. Magnetic properties and microstructures of the Nd-Fe-B magnet powder produced by hydrogen treatment [J]. J. Appl. Phys.,1991,70:3770-3774.
[9]M. Yue, X. B. Liu, Y. F. Xiao, J. X. Zhang. Magnetization reversal mechanism of anisotropic HDDR Nd2Fe14B-based magnet powder [J]. J. Magn. Magn. Mater., 2004,269:227-230.
[10]R. W. Gao, J. C. Zhang, D. H. Zhang, Y. Y. Dai, X. H. Meng, Z. M. Wang, Y. J. Zhang, H. Q. Liu. Dependence of the magnetic properties on the alignment magnetic field for NdFeB bonded magnets made from anisotropic HDDR powders [J]. J. Magn. Magn. Mater.,1999,191:97-100.
[11]H. Kronmuller, K. D. Durst, M. sagawa. Analysis of the magnetic hardening mechanism in RE-Fe-B permanent magnets [J]. J. Magn. Magn. Mater.,1988, 74:291-302.
[12]R. W. Gao, H. Li, S. T. Jiang. L. M. Mei, M. Y. Qiu. Investigations on magnetization reversal processes in oriented sintered Nd-Fe-B alloys [J]. J. Magn. Magn. Mater.,1991,95:205-212.
[13]A. Sakuma, S. Takeda. Calculation of demagnetization curves of NdFeB magnets based on inhomogeneous nucleation [J]. IEEE. Trans. Mag.,1990, 26(50):1745-1747.
[14]B. Edwards, D. I. Paul. Magnetic-field orientation and coercivity [J]. J. Appl. Phys.,1994,76:6271-6273.
[15]R. W. Gao, D. H. Zhang, S. T. Jiang. Coercivity and its dependence on the strength of alignment magnetic field in NdFeB sintered magnets [J]. J. Appl. Phys.,1995,78(2):1156-1159.
[16]D. Li, K. J. Strnat. Domain behavior in sintered NdFeB magnets during field-induced and thermal magnetization change [J]. J. Appl. Phys.,1985, 57:4143-4145.
[17]G. B. Han, R. W. Gao, S. Fu, W. C. Feng, H. Q. Liu, W. Chen, W. Li, Y. Q. Guo. Effective anisotropy between magnetically soft and hard grains in nanocomposite magnets [J]. Appl. Phys. A.,2005,81:579-582.
[18]S. T. Chui, Y. Yu. Domain wall depinning in hard-soft composites [J]. Phys. Review. B.,2001,63:140419(1)-140419 (4).
[19]H. W. Zhang, Z. G. Sun, S. Y. Zhang, B. S. Han, B.G. Shen. Intergrain exchange coupling and coercivity mechanism of nanocrystalline SmFeCuSiC ribbons prepared by melt spinning [J]. Phys. Review. B.,1998,60:64-67.
[20]F. Hirotoshi, I. Hiroshi. Effect of intergranular exchange interaction on
magnetic properties in isotropic Nd-Fe-B magnets [J]. J. Appl. Phys.,1992, 31:1347-1352.
[21]Y. Sun, G. B. Han, B. P. Han, M. Liu, R. W. Gao. Anisotropy of grain in nanoscaled magnetic materials [J]. J. Appl. Phys.,2007,101:063908(1)-063908 (4)
[22]D. S. Xue, G. Z. Chai, X. L. Li, X. L. Fan. Effects of grain size distribution on coercivity and permeability ferromagnets [J]. J. Magn. Magn. Mater.,2008, 320:1541-1543.
[23]T. Takashita, K. Morimoto. Anisotropic Nd-Fe-B bonded magnets made from HDDR powders [J]. J. Appl. Phys.,1996,79:5040-5044.
[24]R. Nakayama, T. Takeshita, M. Itakura, N. Kuwano, K. Oki. Microstructures and crystallographic orientation of crystalline grains in anisotropic Nd-Fe-Co-B-(Ga or Zr) magnet powders produced by the hydrogenation-decomposition-desorption-recombination process [J]. J. Appl. Phys.,1994,76(1):412-417.
[25]R. Nakayama, T. Takeshita. Magnetic properties and microstructures of the Nd-Fe-B system during the hydrogenation-decomposition-desorption-recombination process [J]. J. Appl. Phys.,1993,74:2719-2724.
[26]G B. Han, R. W. Gao, S. S. Yan, H. Q. Liu, S. Fu, W. C. Feng, W. Li, X. M. Li. Effect of exchange-coupling interaction on the effective anisotropy in nanocrystalline Nd2Fe14B material [J]. J. Magn. Magn. Mater.,2004,281:6-10.
[27]K. D. Durst, H. Kronmuller. The coercive field of sintered and melt-spun NdFeB magnets [J]. J. Magn. Magn. Mater.,1987,68:63-75.
[28]R. W. Gao, W. C. Feng, H. Q. Liu, X. M. Li, M. G. Zhu. Exchange-coupling interaction, effective anisotropy and coercivity in nanocomposite permanent materials [J]. J. Appl. Phys.,2003,94(1):664-668.
[29]H. Kronmuller, M. Fischer, R. Seeger, A. Zern. Micromagnetism and microstructure of hard magnetic materials [J]. J. Phys. D.,1996, 29:2274-2283.
[30]M. Gronefeid, H. Kronmuller. Calculation of strayfields near grain edges in permanent magnet material [J]. J. Magn. Magn. Mater.,1989,80:223-228.
[31]钟文定.铁磁学中册[M].北京：科学出版社,1992.p355.
[32]K. Moritmoto, K. Kato, K. Igarashi, R. Nakayama. Magnetic properties of anisotropic Nd-Fe-B HDDR powders prepared from strip cast alloys [J]. J. Alloys. Compd.,2004,366:274-278.
[33]T. Takeshita, R. Nakayama. Magnetic properties and microstructures of the NdFeB magnet powder produced by hydrogen treatment, in Proc.10th Int. Workshop on Rare-Earth Magnets and Their Applications. Kyoto, Japan.1989, 551-557.
[34]P. J. McGuiness, X. J. Zhang, X. J. Yin, I. R. Harris. Hydrogenation, disproportionation and desorption (HDD):An effective processing route for Nd-Fe-B-type magnets [J]. J. Less. Common. Metals.,1990,158:359-364.
[35]M. Liu, Y. Sun, G. B. Han, W. Yang, R. W. Gao. Effect of microstructure on the coercivity of HDDR Nd-Fe-B permanent magnetic alloy [J]. Science. China. G.,2008,51:1557-1564.
[1]Y. Kaneko. Highest performanence of Nd-Fe-B magnet over 55MGOe [J]. IEEE. Trans. Magn.,2000,36:3275-3278.
[2]D. W. Scott, B. M. Ma, Y. L. Liang, C. O. Bounds. Microstructural control of NdFeB cast ingots for achieving 50MGOe sintered magnets [J]. J. Appl. Phys., 1996,79(8):4830-4832.
[3]B. M. Ma, C. O. Bounds. The impact of the directional solidification on the magnetic properties of NdFeB magnets [J]. J. Appl. Phys.,1991,70:6471-6473.
[4]R. Nakayama, T. Takeshita, M. Itakura, N. Kuwano, K. Oki. Microstructures and crystallographic orientation of crystalline grains in anisotropic Nd-Fe-Co-B-(Ga or Zr) magnet powders produced by the hydrogenation- decompositio-desorption- recombination process [J]. J. Appl. Phys.,1994,76(1):412-417.
[5]H. Nakamura, R. Suefuji, S. Sugimoto, M. Okada, M. Homma. Effects of HDDR treatment conditions on magnetic properties of Nd-Fe-B anisotropic powders [J]. J. Appl. Phys.,1994,76(10):6828-6830.
[6]S. Sugimoto, H. Nakamura, K. Kato, D. Book, T. Kagotani, M. Okada, M. Homma. Effect of the disproportionation and recombination stages of the HDDR process on the inducement of anisotropy in Nd-Fe-B magnets [J]. J. Alloys. Compd.,1999,293-295:862-867.
[7]M. Liu, G. B. Han, R.W. Gao. Anisotropic HDDR Nd-Fe-B magnetic powders prepared directly from strip casting alloy flakes [J]. J. Alloys. Compd.,2010, 488:310-313
[8]W. Rodewald, R. Blank, B. Ball, G. W. Reppel, H. D. Zilg. Production of sintered NdFeB magnets with a maximum energy density of 53 MGOe, in Proc.16th Int. Workshop on Rare-Earth Magnets and Their Applications. Sendai, Japan,2000, 119-126.
[9]J. Bernardi, J. Fidler, M. Sagawa, Y. Hirose. Microstructure analysis of strip cast Nd-Fe-B alloys for high (BH)m magnets [J]. J. Appl. Phys.,1998, 83(11):6396-6398.
[10]S. Sasaki, J. Fidler, M. Sagawa. High performance sintered Nd-Fe-B magnets made by new RIP from SC alloys, in Proc.16th Int. Workshop on Rare-Earth Magnets and Their Applications. Sendai, Japan,2000,109-118.
[11]Y. Hirose, H. Hasegawa, S. Sasaki, M. Sagawa. Microstructure of strip cast alloys for high performance NdFeB magnets, in Proc.15th Int. Workshop on Rare-Earth Magnets and Their Applications. Dresden, Germany,1998,77-87.
[12]C. E. Rodriguez Torres, M. B. Fernandez van Raap, F.HSchez, A. F. Pasquevich. EXAFS determination of Hf localization in HDDR-Nd-Fe-B-Hf alloys [J]. Physica B.,2005,362:145-152.
[13]P. de Rango, S. Rivoirard, A. Traverse, D. Fruchart, F.N. Genin. Role of Zr and Ga additions on the hydrogen process of Nd-Fe-B magnets [J]. J. Alloys. Compd.,2003,356-357:579-583.
[14]J. R. Gao, X. P. Song, X. T. Wang. Effects of reduced hydrogen pressure on magnetic properties of HDDR-treated NdFeGaB alloy powders [J]. J. Alloys. Compd.,1998,267:270-273
[15]J. Z. Han, C. L. Tong, A. Z. Sun, Y. F. Xiao. R. Wang. Microstructural changes during the disproportionation of NdFe B alloys [J]. J. Magn. Magn. Mater., 2004,270:136-141.
[1]T. Takeshita, R. Nakayama. Magnetic properties and microstructures of the NdFeB magnet powder produced by the HDDR process-(IV), in Proc.12th Int. Workshop on Rare-Earth Magnets and Their Applications. Canberra, Australia, 1992,670-675.
[2]I. R. Harris. The use of hydrogen in the production of Nd-Fe-B-type magnets and in the assessment of Nd-Fe-B-type alloys and permanent magnets-An update, in Proc.12th Int. Workshop on Rare-Earth Magnets and Their Applications. Canberra, Australia,1992,347-371.
[3]R. N. Faria, B. E. Davies, D. N. Brown, I. R. Harris. Microstructural and magnetic studies of cast and annealed Nd and PrFeCoBZr alloys and HDDR materials [J]. J. Alloys. Compd.,2000,296:223-228.
[4]N. Cannesan, D. N. Brown, A. J. Williams, I. R. Harris. The production and characterisation of highly anisotropic PrFeCoB-type HDDR powders [J]. J. Magn. Magn. Mater.,2001,233,209-218.
[5]K. Morimoto, K. Kato, K. Igarashi, R. Nakayama. Magnetic properties of anisotropic Nd-Fe-B HDDR powders prepared from strip cast alloys [J]. J. Alloys. Compd.,2004,366:274-278.
[6]K. Morimoto, E. Niizuma, R. Nakayama, K. Igarashi. Influences of original alloy microstructure on magnetic properties of isotropic HDDR-treated Nd-Fe-B powder [J]. J. Magn. Magn. Mater.,2003,263:201-207.
[7]M. Uehara, H. Tomizawa, S. Hirosawa, T. Tomida, Y. Maehara. Origin of anisotropy in the HDDR process of Nd2Fe14 B-based alloys [J]. IEEE. Trans. Magn.,1993,29:2770-2772.
[8]K. H. J. Bushow. Trends in rare earth permanent magnets [J]. IEEE. Trans. Magn., 1994,30:565-568.
[9]T. Takashita, K. Morimoto. Anisotropic Nd-Fe-B bonded magnets made from HDDR powders [J]. J. Appl. Phys.,1996,79:5040-5044.
[10]C. E. R.Torres, M. B. F. Raap, F. H. Sanchez, A. F. Pasquevich. EXAFS
determination of Hf localization in HDDR-Nd-Fe-B-Hf alloys [J]. Physica B., 2005,362:145-152.
[11]O. Gutfleisch, A. Teresiak, B. Gebel, K.H. Muller, N. B. Cannesan, D. Brown, I. R. Harris. Metastable borides and the inducement of texture in Pr2Fe14B-type magnets produced by HDDR [J]. IEEE. Trans. Magn.,2001,37:2471-2473.
[12]O. Gutfleisch, G. Drazic. C. Mishima, Y. Honkura. Texture inducement during HDDR processing of NdFeB [J]. IEEE Trans Magn.,2002,38:2958-2960.
[13]G. Yi, J. N. Chapman, D. N. Brown, I. R. Harris. Intermediate phases in the hydrogen disproportionated state of NdFeB-type powders [J]. J. Appl. Phys., 2001,90:1924-1930.
[14]J. Z.Han, C. L. Tong, A. Z. Sun, Y. F. Xiao, R. Wang. Microstructural changes during the disproportionation of Nd13Fe80B7 alloys[J]. J. Magn. Magn. Mater., 2004,270:136-141.
[15]R. Kopp, F. Hagemann, L. Hentschel, J. W. Schmitz, D. Senk. Thin-strip casting-modelling of the combined casting/metal-forming process [J]. J. Mater. Proce. Tech.,1998,80-81:458-462.
[16]W. L. Pei, C. S. He, F. Z. Lian. Structure and magnetic properties of sintered Nd-Fe-B magnets produced by strip casting technique [J]. J. Magn. Magn. Mater.,2002,239:475-478.
[17]Y. Kaneko. Highest performanence of Nd-Fe-B magnet over 55MGOe [J]. IEEE. Trans. Magn.,2000,36:3275-3278.
[18]J. Bernardi, J. Fidler, M. Sagawa, Y. Hirose. Microstructural analysis of strip cast Nd-Fe-B alloys for high (BH)max magnets [J]. J. Appl. Phys.,1998,83: 6396-6398.
[19]F. Vial, F. Joly, E. Nevalainen, M. Sagawa, K. Hiraga, K. T. Park. Improvement of coercivity of sintered NdFeB permanent magnets by heat treatment [J]. J. Magn. Magn. Mater.,2002,242-245:1329-1334.
[20]仝成利,孙爱芝,贾成厂,韩景智,肖耀福,王润.吸氢对HDDR各向异性NdFeB材料的影响[J].稀有金属.,2004,28：971-974.
[21]H. W. Kwon, J. H. Kim. Effect of hydrogen pressure on anisotropy of HDDR-treated Nd-Fe-B-type powder [J]. J. Magn. Magn. Mater.,2006, 304:e222-e224.
[22]Y. Honkura, C. Mishima, N. Hamada, G. Drazic, O. Gutfleisch. Texture memory effect of Nd-Fe-B during hydrogen treatment. [J]. J. Magn. Magn. Mater.,2005, 290-291:1282-1285.
[23]J. R. Gao, X. P. Song, X. T. Wang. Effects of reduced hydrogen pressure on magnetic properties of HDDR-treated NdFeGaB alloy powders [J]. J Alloys. Compd.,1998,267:270-273.
[24]O. Gutfleisch, B. Gebel, N. Mattern. Texture in a ternary Nd16.2Fe78.2B5.6 powder using a modified hydrogenation-disproportionation-desorption-recombination process [J]. J. Magn. Magn. Mater.,2000,210:5-9.
[25]廖达前,连发增,王继杰,付猛,陈玉兰.HDDR工艺条件及均匀化处理对Nd12.6Fe69.3Co11.6B6.0Al0.5合金磁性能的影响[J].功能材料.,2005,36：190-192.
[26]韩景智,孙爱芝,刘涛,肖耀福,王润.HDDR三元NdFeB各向异性材料的制备[J].北京科技大学学报.,2002,24(2)：137-140.
[27]S. Sugimoto, H. Nakamura, K. Kato, D. Book, T. Kagotani, M. Okada, M. Homma. Effect of the disproportionation and recombination stages of the HDDR process on the inducement of anisotropy in Nd-Fe-B magnets [J]. J. Alloys. Compd.,1999,293-295:862-867.
[28]J. R. Gao, X. P. Song, X. T. Wang. Effects of reduced hydrogen pressure on magnetic properties of HDDR-treated NdFeGaB alloy powders [J]. J Alloys. Compd.,1998,267:270-273.
[2]周寿增,董清飞.超强永磁体[M].北京：冶金工艺出版社,1999.p321.
[3]李强,周邦新.快淬NdFeB粉末的TEM样品制备[J].稀有金属材料与工程.,2004,29(4)：283-284.
[4]R. K. Mishra. Microstructure of melt-spun Nd-Fe-B m agneqench magnets [J]. J. Magn. Magn. Mater.,1986,450:54-57.
[5]M. K. Veistinen, E. J. Lavemia, J. C. Baram, N. J. Grant. Flow mechanisms affecting rapid solidification in high pressure gas atomization [J]. Int. J. Powder Metall.,1989,25:89-92.
[6]丘光汉.气体喷雾-水淬工艺制造Al-Si合金粉末[J].中南工业大学学报.,1995,26：484-487.
[7]L. Schultz, J. Wecker, E. Hellstern. Formation and properties of NdFeB prepared by mechanical alloying and solid-state reaction [J]. J. Appl. Phys.,1987, 61:3583-3585.
[8]T. Takeshita. R. Nakayama. Magnetic properties and microstructure of the NdFeB magnet powder produced by hydrogen treatment, in Proc.10th Int. Workshop on Rare-Earth Magnets and Their Applications. Kyoto, Japan,1989, 551-557.
[9]P. J. McGuiness, X. J. Zhang, H. Forsyth, I. R. Harris. Disproportionation in Nd16Fe76B8-type hydrides [J]. J. Less-Comm. Metals.,1990,162:379-387.
[10]高建荣,宋晓平,王笑天.NdFeB合金HDDR工艺的回顾与展望[J].功能材料.,1995,26(5)：395-397.
[11]Y. Kawashita, N. Waki, T. Tayu, T. Sugiyama, H. Ono, H. Koyama, H. Kanno, T. Uchida. Microstructures and magnetic properties of hydrogenation disproportionation desorption recombination-processed Nd-Fe-B materials with different Nd content of 11.0 and 12.6 at.%[J]. J. Alloys. Compd.,2003,
360:322-329.
[12]D. Book, I. R. Harris.The disproportionation of Nd2Fe14B under hydrogen in Nd-Fe-B alloys [J]. IEEE. Trans. Magn.,1992,28:2145-2147.
[13]M. Matsuura, A. Ashfaq, M. Sakurai, T. Tomida, N. Sano, S. Hirosawa. Ga site occupancy in HDDR-treated Nd2Fe14B based alloy by XAFS [J]. J. Alloys. Compd.,1999,293-295:872-876.
[14]R. Nakayama, T. Takeshita, M. Itakura, N. Kuwano, K. Oki. Magnetic properties and microstructures of the Nd-Fe-B magnet powder produced by hydrogen treatment [J]. J. Appl. Phys.,1991,70:3770-3774.
[15]H. Nakamura, S. Sugimoto, T. Tanaka, M. Okada. M. Homma. Effects of additional elements on hydrogen absorption and desorption characteristics of Sm2Fe17 compounds [J]. J Alloys. Compd.,1995, 222:13-17.
[16]H. Nakamura, S. Sugimoto, M. Okada, M. Homma. High-coercivity Sm2Fe17Nx powders produced by HDDR and nitriding processes [J]. Mater. Chem. Phys., 1992,32:280-285.
[17]O. Gutfleisch, B. Gebel, N. Mattern. Texture in a ternary Nd16.2Fe78.2B5.6 powder using a modified hydrogenation-disproportionation-desorption-recombination process [J]. J. Magn. Magn. Mater.,2000,210:5-9.
[18]H. Nakamura, K. Kato, D. Book. S. Sugimoto, M. Homma. Enhancement of coercivity in high remanence HDDR Nd-Fe-B powders [J]. IEEE. Trans. Magn., 1999,35:3274-3276.
[19]S. Sugimoto, N. Koike, D. Book, T. Kagotani, M. Okada, K. Inomata, M. Homma. An improved HDDR treatment for the production of anisotropic Nd-Fe-B ternary powders [J]. J. Alloys. Compd.,2002,330-332:892-896.
[20]刘旭波.博士论文.北京科技大学,2000,p58-59.
[21]K. Morimoto, E. Niizuma, R. Nakayama, K. Igarashi. Influence of original alloy microstructure on magnetic properties of isotropic HDDR-treated Nd-Fe-B powder [J]. J. Magn. Magn. Mater.,2003,263:201-207.
[22]K. Morimoto, K. Kato, K. Igarashi, R. Nakayama. Magnetic properties of anisotropic Nd-Fe-B HDDR powders prepared from strip cast alloys [J]. J Alloys. Compd.,2004,366:274-278.
[23]G. Shi, L. X. Hu, E. D. Wang. Preparation, microstructure and magnetic properties of a nanocrystalline Nd12Fe82B6 alloy by HDDR combined with mechanical milling [J]. J. Magn. Magn. Mater.,2006,301:319-324.
[24]P. J. McGuiness, X. J. Zhang, X. J. Yin, I. R. Harris. Hydrogenation, disproportionation and desorption (HDD):An effective processing route for Nd-Fe-B-type magnets [J]. J. Less. Common. Metals.,1990,158:359-364.
[25]韩景智,孙爱芝,刘涛,肖耀福,王润.HDDR三元NdFeB各向异性材料的制备[J].北京科技大学学报.,2002,24(2)：137-140.
[26]Y. Kawashita, N. Waki, T. Tayu, T. Sugiyama, H. Ono, H. Koyama, H. Kanno, T. Uchida. Magnetic properties of Nd-Fe-B system anisotropic HDDR powder made from segregated master ingots [J]. J. Magn. Magn. Mater.,2004,269: 293-301.
[27]廖达前,连发增,王继杰,付猛,陈玉兰.HDDR工艺条件及均匀化处理对Nd12.6Fe69.3CO11.6B6.0Al0.5合金磁性能的影响[J].功能材料.,2005,36：190-192.
[28]J. R. Gao, X. P. Song, X. T. Wang. Effects of reduced hydrogen pressure on magnetic properties of HDDR-treated NdFeGaB alloy powders [J]. J Alloys. Compd.,1998,267:270-273.
[29]O. Gutfleisch, G. Drazic, C. Mishima, Y. Honkura Texture inducement during HDDR processing of NdFeB [J]. IEEE.Trans. Magn.,2002,38:2958-2960.
[30]O. Gutfleisch, M. Matzinger, J. Fidler, I. R. Harris. Characterisation of solid-HDDR processed Nd16Fe76B8 alloys by means of electron microscopy [J]. J. Magn. Magn. Mater.,1995,147:320-330.
[31]T. Takashita, K. Morimoto. Anisotropic Nd-Fe-B bonded magnets made from HDDR powders [J]. J. Appl. Phys.,1996,79:5040-5044.
[32]T. Takeshita, R. Nakayama. Magnetic properties and microstructures of the Nd-Fe-B magnet powders produced by the hydrogen treatment-(Ⅲ), in Proc.
11th Int. Workshop on Rare-Earth Magnets and Their Applications. Pittsburgh, America,1990,49-71.
[33]R. Nakayama, T. Takeshita. Nd-Fe-B anisotropic magnet powders produced by the HDDR process [J]. J. Alloys Compd.,1993,193:259-261.
[34]R. Nakayama, T. Takeshita, M. Itakura, N. Kuwano, K. Oki. Microstructures and crystallographic orientation of crystalline grains in anisotropic Nd-Fe-Co-B-(Ga or Zr) magnet powders produced by the hydrogenation-decomposition-desorption-recombination process [J]. J. Appl. Phys.,1994,76(1):412-417.
[35]S. Hirosawa, M. Uehara, S. Mino, N. Ishigaki, T. Tomida. New aspects of Nd-Fe-B-based hydrogenation-disproportionationdesorption-recombination powders and anisotropic bonded magnets made from them:Microstructure and magnetic properties [J]. J. Appl. Phys.,1997,81(8):4821-4826.
[36]S. Sugimoto, H. Nakamura, K. Kato, D. Book, T. Kagotani, M. Okada, M. Homma. Effect of the disproportionation and recombination stages of the HDDR process on the inducement of anisotropy in Nd-Fe-B magnets [J]. J. Alloys Compd.,1999,293-295:862-867.
[37]O. Gutfleisch, B. Gebel, M. Kubis, K. H. Muller, L. Schultz. Modified HDDR procedures applied to NdFeB alloys [J]. IEEE. Trans. Magn.,1999,35:3250-3252.
[38]K. Morimoto, R. Nakayama, K. Mori, K. Igarashi, Y. Ishii, M. Itakura, N. Kuwano, K. Oki. Anisotropic NdFeB-based magnet powder with high remanence produced by modified HDDR process [J]. IEEE. Trans. Magn.1999, 35:3253-3255.
[39]C. Mishima, N. Hamada, H. Mitarai, Y. Honkura. Development of a Co-free NdFeB anisotropic bonded magnet produced from the d-HDDR processed powder [J]. IEEE. Trans. Magn.2001,37:2467-2470.
[40]O. Gutfleisch, K. Khlopkov, A. Teresiak, K. H. Muller, G. Drazic, C. Mishima, Y. Honkura. Memory of Texture During HDDR Processing of NdFeB [J]. IEEE. Trans. Magn.2003,39:2926-2931.
[41]C. Mishima, N. Hamada, H. Mitarai, Y. Honkura. Magnetic properties of NdFeB anisotropic magnet powder produced by the d-HDDR method, in Proc. 16th Int. Workshop on Rare-Earth Magnets and Their Applications. Sendai, Japan,2000,873-880.
[42]T. Tomida, N. Sano, M. Uehara. Orientational memory site in hydrogenation disproportionation desorptionrecombination process of anisotropic Nd2Fe14B-based magnets [J]. J. Appl. Phys.,1997,81(11):7170-7174
[43]I. R. Harris. The use of hydrogen in the production of Nd-Fe-B-type magnets and in the assessment of Nd-Fe-B-type alloys and permanent magnets-An update, in Proc.12th Int. Workshop on Rare-Earth Magnets and Their Applications. Canberra, Australia,1992,347-371.
[44]K. H. J. Bushow. Trends in rare earth permanent magnets [J]. IEEE.Tran. Magn., 1994,30:565-568.
[45]H. Nakamura, R. Suefuji, S. Sugimoto, M. Okada, M. Homma. Effects of HDDR treatment conditions on magnetic properties of Nd-Fe-B anisotropic powders [J]. J. Appl. Phys.,1994,76 (10):6828-6830.
[46]G. Yi, J. N. Chapman, D. N. Brown, I. R. Harris. Intermediate phasesin the hydrogen disproportionated state of NdFeB-type powders [J]. J. Appl. Phys., 2001,90:1924-1930.
[47]T. Tomida, N. Sano, K. Hanafusa, H.Tomizawa, S. Hirosawa. Intermediate hydrogenation phase in the hydrogenation-disproportionation-recombination process of Nd2Fe14B-based anisotropic magnets [J]. Acta. Mater.,1999, 47(3):875-885.
[48]O. Gutfleisch, A. Teresiak, B. Gebel, K. H. Muller, N. B. Cannesan, D. Brown, I. R. Harris. Metastable borides and the inducement of texture in Pr2Fe14B-type magnets produced by HDDR [J]. IEEE. Trans. Magn.,2001,37(4):2471-2473.
[49]J. Z. Han, C. L. Tong, A. Z. Sun, Y. F. Xiao, R. Wang. Microstructural changes during the disproportionation of Nd13Fe80B7 alloys [J]. J. Magn. Magn. Mater., 2004,270:136-141.
[50]R. Nakayama, T. Mugginess. Grain-size dependence of remanence and coercive field of isotropic nanocrystalline composite permanent magnets [J]. J. Magn. Magn. Mater.,1996,153:35-49.
[51]岳明,刘旭波,肖耀福,张久兴.HDDR各向异性NdFeB矫顽力机理的研究[J].稀有金属材料与工程.,2003,32(7)：490-493.
[52]R. W. Gao, J. C. Zhang, D. H. Zhang, Y. Y. Dai, X. H. Meng, Z. M. Wang, Y. J. Zhang, H. Q. Liu. Dependence of the magnetic properties on the alignment magnetic field for NdFeB bonded magnets made from anisotropic HDDR powders [J]. J. Magn. Magn. Mater.,1999,191:97-100.
[1]O. Gutfleisch, G. Drazic, C. Mishima, Y. Honkura. Texture inducement during HDDR processing of NdFeB [J]. IEEE. Trans. Magn.,2002,38:2958-2960.
[2]T. Takeshita, R. Nakayama. Nd-Fe-B anisotropic magnet powders by the HDDR process, in Proc.12th Int. Workshop on Rare-Earth Magnets and Their Applications. Canberra, Australia,1992,259-261.
[3]R. Nakayama, T. Takeshita. M. Itakura, N. Kuwano, K. Oki. Magnetic properties and microstructures of the Nd-Fe-B magnet powder produced by hydrogen treatment [J]. J. Appl. Phys.,1990,67(9):4665-4665.
[4]S. Sugimoto, O. Gutfleisch, I. R. Harris. Resistivity measurements on hydrogenation disproportionation desorption recombination phenomena in Nd-Fe-B alloys with Co, Ga and Zr additions [J]. J. Alloys. Compd.,1997, 260:284-291.
[5]S. B. Rybalka, E.V. Dodonova, V. A. Didus. Some kinetic and microstructural aspects during FeB alloys hydrogen-induced phase transformations in Nd2Fe14B alloys [J]. J. Alloys. Compd.,2005,404-406:588-594.
[6]K. Morimoto, K. Igarashi, K. Kato, R. Nakayama, M.Yagi. Anisotropic HDDR-treated Nd-Fe-B alloy flakes for mechanically oriented composite magnets [J]. J. Alloys. Compd.,2005,393:311-315.
[7]W. Chen, R. W. Gao, M.G. Zhu, W. Pan, W. Li, X. M. Li, G. B. Han, W.C. Feng, B. Wang. Magnetic properties and coercivity mechanism of isotropic HDDR NdFeB bonded magnets with Co and Dy addition [J]. J. Magn. Magn. Mater., 2003,261:222-227.
[8]R. Nakayama, T. Takeshita, M. Itakura, N. Kuwano, K. Oki. Magnetic properties and microstructures of the Nd-Fe-B magnet powder produced by hydrogen treatment [J]. J. Appl. Phys.,1991,70:3770-3774.
[9]M. Yue, X. B. Liu, Y. F. Xiao, J. X. Zhang. Magnetization reversal mechanism of anisotropic HDDR Nd2Fe14B-based magnet powder [J]. J. Magn. Magn. Mater., 2004,269:227-230.
[10]R. W. Gao, J. C. Zhang, D. H. Zhang, Y. Y. Dai, X. H. Meng, Z. M. Wang, Y. J. Zhang, H. Q. Liu. Dependence of the magnetic properties on the alignment magnetic field for NdFeB bonded magnets made from anisotropic HDDR powders [J]. J. Magn. Magn. Mater.,1999,191:97-100.
[11]H. Kronmuller, K. D. Durst, M. sagawa. Analysis of the magnetic hardening mechanism in RE-Fe-B permanent magnets [J]. J. Magn. Magn. Mater.,1988, 74:291-302.
[12]R. W. Gao, H. Li, S. T. Jiang. L. M. Mei, M. Y. Qiu. Investigations on magnetization reversal processes in oriented sintered Nd-Fe-B alloys [J]. J. Magn. Magn. Mater.,1991,95:205-212.
[13]A. Sakuma, S. Takeda. Calculation of demagnetization curves of NdFeB magnets based on inhomogeneous nucleation [J]. IEEE. Trans. Mag.,1990, 26(50):1745-1747.
[14]B. Edwards, D. I. Paul. Magnetic-field orientation and coercivity [J]. J. Appl. Phys.,1994,76:6271-6273.
[15]R. W. Gao, D. H. Zhang, S. T. Jiang. Coercivity and its dependence on the strength of alignment magnetic field in NdFeB sintered magnets [J]. J. Appl. Phys.,1995,78(2):1156-1159.
[16]D. Li, K. J. Strnat. Domain behavior in sintered NdFeB magnets during field-induced and thermal magnetization change [J]. J. Appl. Phys.,1985, 57:4143-4145.
[17]G. B. Han, R. W. Gao, S. Fu, W. C. Feng, H. Q. Liu, W. Chen, W. Li, Y. Q. Guo. Effective anisotropy between magnetically soft and hard grains in nanocomposite magnets [J]. Appl. Phys. A.,2005,81:579-582.
[18]S. T. Chui, Y. Yu. Domain wall depinning in hard-soft composites [J]. Phys. Review. B.,2001,63:140419(1)-140419 (4).
[19]H. W. Zhang, Z. G. Sun, S. Y. Zhang, B. S. Han, B.G. Shen. Intergrain exchange coupling and coercivity mechanism of nanocrystalline SmFeCuSiC ribbons prepared by melt spinning [J]. Phys. Review. B.,1998,60:64-67.
[20]F. Hirotoshi, I. Hiroshi. Effect of intergranular exchange interaction on
magnetic properties in isotropic Nd-Fe-B magnets [J]. J. Appl. Phys.,1992, 31:1347-1352.
[21]Y. Sun, G. B. Han, B. P. Han, M. Liu, R. W. Gao. Anisotropy of grain in nanoscaled magnetic materials [J]. J. Appl. Phys.,2007,101:063908(1)-063908 (4)
[22]D. S. Xue, G. Z. Chai, X. L. Li, X. L. Fan. Effects of grain size distribution on coercivity and permeability ferromagnets [J]. J. Magn. Magn. Mater.,2008, 320:1541-1543.
[23]T. Takashita, K. Morimoto. Anisotropic Nd-Fe-B bonded magnets made from HDDR powders [J]. J. Appl. Phys.,1996,79:5040-5044.
[24]R. Nakayama, T. Takeshita, M. Itakura, N. Kuwano, K. Oki. Microstructures and crystallographic orientation of crystalline grains in anisotropic Nd-Fe-Co-B-(Ga or Zr) magnet powders produced by the hydrogenation-decomposition-desorption-recombination process [J]. J. Appl. Phys.,1994,76(1):412-417.
[25]R. Nakayama, T. Takeshita. Magnetic properties and microstructures of the Nd-Fe-B system during the hydrogenation-decomposition-desorption-recombination process [J]. J. Appl. Phys.,1993,74:2719-2724.
[26]G B. Han, R. W. Gao, S. S. Yan, H. Q. Liu, S. Fu, W. C. Feng, W. Li, X. M. Li. Effect of exchange-coupling interaction on the effective anisotropy in nanocrystalline Nd2Fe14B material [J]. J. Magn. Magn. Mater.,2004,281:6-10.
[27]K. D. Durst, H. Kronmuller. The coercive field of sintered and melt-spun NdFeB magnets [J]. J. Magn. Magn. Mater.,1987,68:63-75.
[28]R. W. Gao, W. C. Feng, H. Q. Liu, X. M. Li, M. G. Zhu. Exchange-coupling interaction, effective anisotropy and coercivity in nanocomposite permanent materials [J]. J. Appl. Phys.,2003,94(1):664-668.
[29]H. Kronmuller, M. Fischer, R. Seeger, A. Zern. Micromagnetism and microstructure of hard magnetic materials [J]. J. Phys. D.,1996, 29:2274-2283.
[30]M. Gronefeid, H. Kronmuller. Calculation of strayfields near grain edges in permanent magnet material [J]. J. Magn. Magn. Mater.,1989,80:223-228.
[31]钟文定.铁磁学中册[M].北京：科学出版社,1992.p355.
[32]K. Moritmoto, K. Kato, K. Igarashi, R. Nakayama. Magnetic properties of anisotropic Nd-Fe-B HDDR powders prepared from strip cast alloys [J]. J. Alloys. Compd.,2004,366:274-278.
[33]T. Takeshita, R. Nakayama. Magnetic properties and microstructures of the NdFeB magnet powder produced by hydrogen treatment, in Proc.10th Int. Workshop on Rare-Earth Magnets and Their Applications. Kyoto, Japan.1989, 551-557.
[34]P. J. McGuiness, X. J. Zhang, X. J. Yin, I. R. Harris. Hydrogenation, disproportionation and desorption (HDD):An effective processing route for Nd-Fe-B-type magnets [J]. J. Less. Common. Metals.,1990,158:359-364.
[35]M. Liu, Y. Sun, G. B. Han, W. Yang, R. W. Gao. Effect of microstructure on the coercivity of HDDR Nd-Fe-B permanent magnetic alloy [J]. Science. China. G.,2008,51:1557-1564.
[1]Y. Kaneko. Highest performanence of Nd-Fe-B magnet over 55MGOe [J]. IEEE. Trans. Magn.,2000,36:3275-3278.
[2]D. W. Scott, B. M. Ma, Y. L. Liang, C. O. Bounds. Microstructural control of NdFeB cast ingots for achieving 50MGOe sintered magnets [J]. J. Appl. Phys., 1996,79(8):4830-4832.
[3]B. M. Ma, C. O. Bounds. The impact of the directional solidification on the magnetic properties of NdFeB magnets [J]. J. Appl. Phys.,1991,70:6471-6473.
[4]R. Nakayama, T. Takeshita, M. Itakura, N. Kuwano, K. Oki. Microstructures and crystallographic orientation of crystalline grains in anisotropic Nd-Fe-Co-B-(Ga or Zr) magnet powders produced by the hydrogenation- decompositio-desorption- recombination process [J]. J. Appl. Phys.,1994,76(1):412-417.
[5]H. Nakamura, R. Suefuji, S. Sugimoto, M. Okada, M. Homma. Effects of HDDR treatment conditions on magnetic properties of Nd-Fe-B anisotropic powders [J]. J. Appl. Phys.,1994,76(10):6828-6830.
[6]S. Sugimoto, H. Nakamura, K. Kato, D. Book, T. Kagotani, M. Okada, M. Homma. Effect of the disproportionation and recombination stages of the HDDR process on the inducement of anisotropy in Nd-Fe-B magnets [J]. J. Alloys. Compd.,1999,293-295:862-867.
[7]M. Liu, G. B. Han, R.W. Gao. Anisotropic HDDR Nd-Fe-B magnetic powders prepared directly from strip casting alloy flakes [J]. J. Alloys. Compd.,2010, 488:310-313
[8]W. Rodewald, R. Blank, B. Ball, G. W. Reppel, H. D. Zilg. Production of sintered NdFeB magnets with a maximum energy density of 53 MGOe, in Proc.16th Int. Workshop on Rare-Earth Magnets and Their Applications. Sendai, Japan,2000, 119-126.
[9]J. Bernardi, J. Fidler, M. Sagawa, Y. Hirose. Microstructure analysis of strip cast Nd-Fe-B alloys for high (BH)m magnets [J]. J. Appl. Phys.,1998, 83(11):6396-6398.
[10]S. Sasaki, J. Fidler, M. Sagawa. High performance sintered Nd-Fe-B magnets made by new RIP from SC alloys, in Proc.16th Int. Workshop on Rare-Earth Magnets and Their Applications. Sendai, Japan,2000,109-118.
[11]Y. Hirose, H. Hasegawa, S. Sasaki, M. Sagawa. Microstructure of strip cast alloys for high performance NdFeB magnets, in Proc.15th Int. Workshop on Rare-Earth Magnets and Their Applications. Dresden, Germany,1998,77-87.
[12]C. E. Rodriguez Torres, M. B. Fernandez van Raap, F.HSchez, A. F. Pasquevich. EXAFS determination of Hf localization in HDDR-Nd-Fe-B-Hf alloys [J]. Physica B.,2005,362:145-152.
[13]P. de Rango, S. Rivoirard, A. Traverse, D. Fruchart, F.N. Genin. Role of Zr and Ga additions on the hydrogen process of Nd-Fe-B magnets [J]. J. Alloys. Compd.,2003,356-357:579-583.
[14]J. R. Gao, X. P. Song, X. T. Wang. Effects of reduced hydrogen pressure on magnetic properties of HDDR-treated NdFeGaB alloy powders [J]. J. Alloys. Compd.,1998,267:270-273
[15]J. Z. Han, C. L. Tong, A. Z. Sun, Y. F. Xiao. R. Wang. Microstructural changes during the disproportionation of NdFe B alloys [J]. J. Magn. Magn. Mater., 2004,270:136-141.
[1]T. Takeshita, R. Nakayama. Magnetic properties and microstructures of the NdFeB magnet powder produced by the HDDR process-(IV), in Proc.12th Int. Workshop on Rare-Earth Magnets and Their Applications. Canberra, Australia, 1992,670-675.
[2]I. R. Harris. The use of hydrogen in the production of Nd-Fe-B-type magnets and in the assessment of Nd-Fe-B-type alloys and permanent magnets-An update, in Proc.12th Int. Workshop on Rare-Earth Magnets and Their Applications. Canberra, Australia,1992,347-371.
[3]R. N. Faria, B. E. Davies, D. N. Brown, I. R. Harris. Microstructural and magnetic studies of cast and annealed Nd and PrFeCoBZr alloys and HDDR materials [J]. J. Alloys. Compd.,2000,296:223-228.
[4]N. Cannesan, D. N. Brown, A. J. Williams, I. R. Harris. The production and characterisation of highly anisotropic PrFeCoB-type HDDR powders [J]. J. Magn. Magn. Mater.,2001,233,209-218.
[5]K. Morimoto, K. Kato, K. Igarashi, R. Nakayama. Magnetic properties of anisotropic Nd-Fe-B HDDR powders prepared from strip cast alloys [J]. J. Alloys. Compd.,2004,366:274-278.
[6]K. Morimoto, E. Niizuma, R. Nakayama, K. Igarashi. Influences of original alloy microstructure on magnetic properties of isotropic HDDR-treated Nd-Fe-B powder [J]. J. Magn. Magn. Mater.,2003,263:201-207.
[7]M. Uehara, H. Tomizawa, S. Hirosawa, T. Tomida, Y. Maehara. Origin of anisotropy in the HDDR process of Nd2Fe14 B-based alloys [J]. IEEE. Trans. Magn.,1993,29:2770-2772.
[8]K. H. J. Bushow. Trends in rare earth permanent magnets [J]. IEEE. Trans. Magn., 1994,30:565-568.
[9]T. Takashita, K. Morimoto. Anisotropic Nd-Fe-B bonded magnets made from HDDR powders [J]. J. Appl. Phys.,1996,79:5040-5044.
[10]C. E. R.Torres, M. B. F. Raap, F. H. Sanchez, A. F. Pasquevich. EXAFS
determination of Hf localization in HDDR-Nd-Fe-B-Hf alloys [J]. Physica B., 2005,362:145-152.
[11]O. Gutfleisch, A. Teresiak, B. Gebel, K.H. Muller, N. B. Cannesan, D. Brown, I. R. Harris. Metastable borides and the inducement of texture in Pr2Fe14B-type magnets produced by HDDR [J]. IEEE. Trans. Magn.,2001,37:2471-2473.
[12]O. Gutfleisch, G. Drazic. C. Mishima, Y. Honkura. Texture inducement during HDDR processing of NdFeB [J]. IEEE Trans Magn.,2002,38:2958-2960.
[13]G. Yi, J. N. Chapman, D. N. Brown, I. R. Harris. Intermediate phases in the hydrogen disproportionated state of NdFeB-type powders [J]. J. Appl. Phys., 2001,90:1924-1930.
[14]J. Z.Han, C. L. Tong, A. Z. Sun, Y. F. Xiao, R. Wang. Microstructural changes during the disproportionation of Nd13Fe80B7 alloys[J]. J. Magn. Magn. Mater., 2004,270:136-141.
[15]R. Kopp, F. Hagemann, L. Hentschel, J. W. Schmitz, D. Senk. Thin-strip casting-modelling of the combined casting/metal-forming process [J]. J. Mater. Proce. Tech.,1998,80-81:458-462.
[16]W. L. Pei, C. S. He, F. Z. Lian. Structure and magnetic properties of sintered Nd-Fe-B magnets produced by strip casting technique [J]. J. Magn. Magn. Mater.,2002,239:475-478.
[17]Y. Kaneko. Highest performanence of Nd-Fe-B magnet over 55MGOe [J]. IEEE. Trans. Magn.,2000,36:3275-3278.
[18]J. Bernardi, J. Fidler, M. Sagawa, Y. Hirose. Microstructural analysis of strip cast Nd-Fe-B alloys for high (BH)max magnets [J]. J. Appl. Phys.,1998,83: 6396-6398.
[19]F. Vial, F. Joly, E. Nevalainen, M. Sagawa, K. Hiraga, K. T. Park. Improvement of coercivity of sintered NdFeB permanent magnets by heat treatment [J]. J. Magn. Magn. Mater.,2002,242-245:1329-1334.
[20]仝成利,孙爱芝,贾成厂,韩景智,肖耀福,王润.吸氢对HDDR各向异性NdFeB材料的影响[J].稀有金属.,2004,28：971-974.
[21]H. W. Kwon, J. H. Kim. Effect of hydrogen pressure on anisotropy of HDDR-treated Nd-Fe-B-type powder [J]. J. Magn. Magn. Mater.,2006, 304:e222-e224.
[22]Y. Honkura, C. Mishima, N. Hamada, G. Drazic, O. Gutfleisch. Texture memory effect of Nd-Fe-B during hydrogen treatment. [J]. J. Magn. Magn. Mater.,2005, 290-291:1282-1285.
[23]J. R. Gao, X. P. Song, X. T. Wang. Effects of reduced hydrogen pressure on magnetic properties of HDDR-treated NdFeGaB alloy powders [J]. J Alloys. Compd.,1998,267:270-273.
[24]O. Gutfleisch, B. Gebel, N. Mattern. Texture in a ternary Nd16.2Fe78.2B5.6 powder using a modified hydrogenation-disproportionation-desorption-recombination process [J]. J. Magn. Magn. Mater.,2000,210:5-9.
[25]廖达前,连发增,王继杰,付猛,陈玉兰.HDDR工艺条件及均匀化处理对Nd12.6Fe69.3Co11.6B6.0Al0.5合金磁性能的影响[J].功能材料.,2005,36：190-192.
[26]韩景智,孙爱芝,刘涛,肖耀福,王润.HDDR三元NdFeB各向异性材料的制备[J].北京科技大学学报.,2002,24(2)：137-140.
[27]S. Sugimoto, H. Nakamura, K. Kato, D. Book, T. Kagotani, M. Okada, M. Homma. Effect of the disproportionation and recombination stages of the HDDR process on the inducement of anisotropy in Nd-Fe-B magnets [J]. J. Alloys. Compd.,1999,293-295:862-867.
[28]J. R. Gao, X. P. Song, X. T. Wang. Effects of reduced hydrogen pressure on magnetic properties of HDDR-treated NdFeGaB alloy powders [J]. J Alloys. Compd.,1998,267:270-273.