本文關(guān)鍵詞：資源節(jié)約型稀土永磁材料的高性能化研究　出處：《浙江大學(xué)》2017年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 燒結(jié)Nd-Fe-B 多主相磁體 晶界相 晶界重構(gòu) 矯頑力

【摘要】：釹鐵硼是目前磁性最強(qiáng)、應(yīng)用最廣、消耗稀土最多的永磁材料。釹鐵硼的多年快速增長(zhǎng),導(dǎo)致我國(guó)稀土資源利用極不平衡,其高度依賴的Nd、Pr、Dy、Tb等昂貴稀土資源日益緊缺,而Ce、La等廉價(jià)的高豐度稀土則大量積壓。減少昂貴的重稀土 Tb、Dy和擴(kuò)大高豐度的Ce、La在釹鐵硼中的應(yīng)用,發(fā)展低成本高性能磁體,已成為稀土永磁材料基礎(chǔ)研究的重要方向。釹鐵硼的強(qiáng)磁性源于2:14:1四方相的內(nèi)稟硬磁性。為滿足高溫應(yīng)用,通常在Nd-Fe-B中添加大量的重稀土 Tb/Dy提高2:14:1相的各向異性場(chǎng)以提高矯頑力,但它導(dǎo)致磁能積降低,且顯著增加成本;另一方面,Ce/La_2Fe_(14)B相的內(nèi)稟磁性遠(yuǎn)弱于Nd/Pr2Fe14B,過(guò)去在釹鐵硼中極少使用。因此,如何在不用或者盡可能少用Dy/Tb的情況下獲得高矯頑力和抑制添加Ce/La導(dǎo)致的磁稀釋效應(yīng)是研制低成本高性能磁體的重要挑戰(zhàn)。針對(duì)上述問(wèn)題,本文從“減法”和“加法”兩方面著手,開(kāi)展了資源節(jié)約型稀土永磁材料的高性能化研究:一是通過(guò)設(shè)計(jì)含Dy的新晶界相,實(shí)現(xiàn)Dy在液相燒結(jié)過(guò)程中向主相晶粒邊界層擴(kuò)散,增強(qiáng)局域各向異性,極大降低了高矯頑力磁體中重稀土用量;二是構(gòu)筑多主相結(jié)構(gòu),即Ce在2:14:1相中非均勻取代Nd,利用不同內(nèi)稟磁性主相間的磁耦合作用增強(qiáng)磁性能,成功研制出高Ce取代量的高性能磁體。主要?jiǎng)?chuàng)新點(diǎn)如下:設(shè)計(jì)了(Pr,Dy,Cu)-H_x氫化物,重構(gòu)Nd-Fe-B磁體晶界相,基于脫氫后元素的商活性實(shí)現(xiàn)Dy向主相邊界層的商效擴(kuò)散,增強(qiáng)局域磁晶各向異性,顯著提商了重稀土在高矯頑力磁體中的利用效率。傳統(tǒng)的直接重稀土合金化方法制備高矯頑力磁體(～20 kOe),需要添加2.0 at.%左右的Dy。晶界添加純金屬元素Dy或者含Dy合金粉末,在燒結(jié)和熱處理過(guò)程中,Dy除了部分的向2:14:1主相晶粒擴(kuò)散,依舊有大量的Dy元素在晶界上富集,導(dǎo)致了重稀土元素的利用效率低。本文設(shè)計(jì)了 Dy濃度較低的晶界相氫化物(Pr,Dy,Cu)-H_x,在高溫?zé)Y(jié)和熱處理擴(kuò)散過(guò)程中,利用氫化物脫氫后的高活性,使重稀土元素Dy向主相邊界層高效擴(kuò)散,并降低Dy元素在晶界相中的濃度,在僅添加0.32 at.%的Dy時(shí),矯頑力力從15.0 kOe提升到18.2 kOe,提升幅度為21.3%,單位原子百分比的Dy對(duì)矯頑力的貢獻(xiàn)高達(dá)10.9 kOe,有效提高了重稀土元素Dy的利用效率。在掌握多主相Nd-Ce-Fe-B磁體的磁性能變化規(guī)律的基礎(chǔ)上,成功制備出高Ce取代量的商性能燒結(jié)磁體。采用雙主相工藝,Ce和Nd在主相中高度非均勻分布,主相間的長(zhǎng)程磁相互作用使磁體磁性能尤其是矯頑力遠(yuǎn)高于相同平均成分、Ce在主相中均勻分布的單主相磁體。發(fā)現(xiàn)少量的Ce取代,多主相磁體退磁曲線的方形度Kk/Hcj下降較多。隨Ce取代量提高,磁體在反磁化過(guò)程中表現(xiàn)出類似“單相”的行為,方形度得以回復(fù)到94%以上。此外,多主相磁體的熱處理工藝對(duì)磁性能的影響更為復(fù)雜:一方面,熱處理改善晶界相分布狀態(tài),有利于抑制主相晶粒間的短程磁相互作用(提高矯頑力);另一方面,熱處理進(jìn)一步促進(jìn)稀土元素在主相晶粒間的互擴(kuò)散,趨向形成與單主相磁體類似的Ce均分分布,弱化主相間的長(zhǎng)程磁相互作用(降低矯頑力)。基于兩種作用的競(jìng)爭(zhēng)關(guān)系,通過(guò)改善和優(yōu)化燒結(jié)和熱處理工藝,在保持Ce非均勻分布的多主相結(jié)構(gòu)的同時(shí)形成連續(xù)均勻分布的晶界相,成功制備出高Ce取代量、高性能的RE-Fe-B多主相燒結(jié)磁體,當(dāng)45wt.%Ce取代Nd時(shí),磁體的綜合磁性能依舊保持在Hcj=9.0kOe,Br=12.4kG,(BH)max=36.7MGOe。掌握了高Ce取代量RE-Fe-B磁體的晶界相組織演變規(guī)律,并揭示了其對(duì)磁性能作用機(jī)理。除了多主相磁體中晶粒間的長(zhǎng)程磁相互作用外,晶界相顯微組織對(duì)磁性能尤其是矯頑力也有重要影響。本文發(fā)現(xiàn)在高Ce取代量的Nd-Ce-Fe-B磁粉中出現(xiàn)少量的REFe_2相,遺傳到最后的多主相磁體中,以連續(xù)的晶界相組織分布在2:14:1相晶粒間,對(duì)磁體的矯頑力起正面作用。由于REFe_2相熔點(diǎn)(978℃)低于2:14:1相,在高溫(1030℃)燒結(jié)過(guò)程中熔化,增加了液相體積分?jǐn)?shù),改善了晶界相與主相之間的潤(rùn)濕性,形成了連續(xù)分布晶界相,弱化主相晶粒之間的短程磁相互作用。洛倫茲透射電鏡(L-TEM)證明了晶界組織的優(yōu)化可以有效抑制晶粒之間短程交換作用;不同主相晶粒之間長(zhǎng)程的靜磁相互作用依舊存在,從而在反磁化過(guò)程中,有效各向異性強(qiáng)的主相晶粒抑制各向異性弱的晶粒磁化翻轉(zhuǎn)。上述兩個(gè)因素對(duì)保持多主相燒結(jié)磁體的矯頑力都具有重要作用。
[Abstract]:NdFeB magnetic current is the strongest, the most widely used, the consumption of rare-earth permanent magnet material. Most of the years of NdFeB rapid growth, resulting in rare earth resource utilization in China is extremely uneven, which is highly dependent on the Nd, Pr, Dy, Tb and other expensive rare earth resources become increasingly scarce, while Ce, La and other cheap high the abundance of rare earth overstock. Less expensive heavy rare earth Tb, Dy and the expansion of high abundance of Ce, the application of La in the development of NdFeB magnets, high performance and low cost, has become an important direction of rare earth permanent magnet materials research. The ferromagnetic source of NdFeB in tetragonal 2:14:1 intrinsic hard magnetic. To meet the high temperature application, usually with heavy rare earth Tb/Dy in a lot of Nd-Fe-B to improve the anisotropy field of 2:14:1 phase to improve the coercivity, but it leads to lower energy product, and significantly increase the cost; on the other hand, Ce/La_2Fe_ (14) B is the intrinsic magnetic properties is much weaker than in the past Nd/Pr2Fe14B, nd iron Boron rarely used. Therefore, how to use or as little as possible with Dy/Tb under the condition of high coercive force and magnetic inhibition caused by Ce/La dilution effect is an important challenge for development of low cost high performance magnets. Aiming at the above problems, this article from the "subtraction" and "addition" two aspects to carry out. Study on high performance resource conservation of rare earth permanent magnet materials: one is through the new grain boundary design phase containing Dy, Dy in the liquid phase sintering process to the main phase grain boundary layer diffusion, enhanced local anisotropy, which greatly reduces the amount of heavy rare earth magnets with high coercivity; two is to build a multi main phase the structure of Ce in 2:14:1 phase, non uniform to replace Nd, using magnetic coupling different intrinsic magnetic properties and magnetic properties of main reinforced, successfully developed a high amount of Ce to replace the high performance magnets. The main innovations are as follows: Design (Pr, Dy, Cu) -H_x hydride, Nd- reconstruction Fe-B grain boundary phase, the dehydrogenation of elements taking the activities of Dy to the main phase boundary layer diffusion based on business efficiency, enhance the local magnetic anisotropy, improve business efficiency in high coercivity magnets. The heavy rare earth direct heavy rare earth alloying the traditional method of preparing high coercivity magnets (20 ~ kOe), need to add the Dy. grain boundaries around 2 at.% with pure metal Dy or Dy containing alloy powder during sintering and heat treatment process, in addition to the part of the Dy diffusion to the 2:14:1 main phase grain, there is still a large number of Dy elements enriched in grain boundaries, resulting in a heavy rare earth element utilization efficiency is low grain boundary. This paper designed the lower concentration of Dy phase (Pr, Dy, Cu by -H_x), in high temperature sintering and thermal diffusion process, high activity after using hydride dehydrogenation, the heavy rare earth element Dy to the main phase boundary layer, diffusion, and reduce the Dy element in the grain boundary phase concentration Only in degree, adding 0.32 at.% of Dy, the coercivity force increased from 15 kOe to 18.2 kOe, to enhance the rate of 21.3% units, atomic percentage of Dy contribution to the coercive force of up to 10.9 kOe, effectively improve the utilization efficiency of heavy rare earth elements Dy. Based the variation in magnetic multi master master Nd-Ce-Fe-B magnet on the successful preparation of high performance sintered magnets Ce to replace the taking amount. By double main phase process, Ce and Nd in the primary phase of highly inhomogeneous distribution, long-range magnetic interaction and main magnetic properties especially the coercivity is much higher than that of the same average composition, in uniform distribution of Ce the main phase of the single phase magnet. Found a small amount of Ce substitution, multiple main magnets of the demagnetization curve rectangularity of Kk/Hcj decreased more. With the Ce content increased, the magnet in the reversal process showed a similar "phase" behavior, to return to more than 94% square degrees. In addition, many Effect of heat treatment on the magnetic properties of the magnet main phase is more complex: on the one hand, the heat treatment improved the grain boundary phase distribution, is conducive to inhibit the interaction between the main phase grain short-range (magnetic coercivity improving); on the other hand, to further promote the heat treatment of rare earth elements in the main phase grain diffusion, tend to form with the single main magnets of Ce were similar distribution, interaction and weak main Cheng Ci (lower coercivity). Competition between the two effects on, by improving and optimizing the sintering and heat treatment process, while maintaining the Ce non uniformly distributed multi main phase structure at the same time the formation of grain boundary continuous uniform distribution the phase was successfully prepared by high Ce content, high performance RE-Fe-B main phase sintered magnets, when 45wt.%Ce replaced Nd, integrated magnets can remain in the Hcj=9.0kOe, Br=12.4kG, max=36.7MGOe. (BH) have high Ce content RE-Fe-B magnet The grain boundary phase microstructure evolution, and reveal the mechanism of magnetic properties. In addition to the main phase in the magnet long-range magnetic interaction between grain and grain boundary phase microstructure on magnetic properties especially the coercivity have an important influence. The paper found that instead of a small amount of REFe_2 phase Nd-Ce-Fe-B magnetic powder in Ce, to the end of the main phase of genetic multi magnet, with continuous grain boundary phase tissue distribution in 2:14:1 grains, the coercive force plays a positive role. Due to the REFe_2 phase (978 DEG C) below the melting point of 2:14:1 phase at high temperature (1030 DEG C) melting and sintering process, adding liquid volume fraction, grain boundary phase and improve the wettability between the main phase, forming a continuous distribution of grain boundary phase, weakening the interaction between the main phase grains. Lorenz short-range magnetic transmission electron microscopy (L-TEM) proved that the optimal organization can restrain the grain boundary between the short-range exchange Effect; magnetostatic interaction still exists in long range between different main phase grain, resulting in the magnetization reversal process, effective strong anisotropy of main phase grain inhibiting grain magnetization reversal. Weak anisotropy plays an important role in the above two factors to keep the main phase of sintered magnet coercivity.

【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TM273

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本文編號(hào)：1388511