呂 蒙, 孔 拓, 朱明原, 胡業(yè)旻, 金紅明, 李文獻(xiàn), 李 瑛

(上海大學(xué) 材料科學(xué)與工程學(xué)院 微結(jié)構(gòu)重點(diǎn)實(shí)驗(yàn)室,上海 200072)

非稀土金屬及合金化合物改性燒結(jié)NdFeB磁體的研究進(jìn)展

呂 蒙, 孔 拓, 朱明原, 胡業(yè)旻, 金紅明, 李文獻(xiàn)*, 李 瑛*

(上海大學(xué) 材料科學(xué)與工程學(xué)院 微結(jié)構(gòu)重點(diǎn)實(shí)驗(yàn)室,上海 200072)

研究發(fā)現(xiàn),燒結(jié)釹鐵硼(NdFeB)磁體的矯頑力(HC)、腐蝕性與晶界相成分、微觀結(jié)構(gòu)息息相關(guān).傳統(tǒng)熔煉添加重稀土元素雖可改善晶界相提高磁體的HC及抗蝕性,但同時(shí)也使添加物均勻地分布于主相,引起稀磁效應(yīng)并使成本增加.通過(guò)晶界添加非稀土物質(zhì)調(diào)控磁體晶界相,可優(yōu)化晶界相微觀結(jié)構(gòu),提高其電極電位及潤(rùn)濕性,從而在磁體HC和耐蝕性得以改善的同時(shí),降低磁體中重稀土元素的用量及成本.對(duì)近些年晶界添加非稀土金屬及合金化合物調(diào)控?zé)Y(jié)NdFeB晶界相成分、微觀結(jié)構(gòu)及其對(duì)磁體HC、抗蝕性影響的部分研究進(jìn)行了歸納.

燒結(jié)NdFeB; 晶界擴(kuò)散; 矯頑力; 抗蝕性; 微觀結(jié)構(gòu); 非稀土金屬及合金化合物

0 前 言

1983年日本住友特殊金屬公司首次制備出釹鐵硼(NdFeB)永磁體[1],由于其具有遠(yuǎn)高于其他磁體的磁性能且不含貴稀土元素Sm及戰(zhàn)略性元素Co[2],顯著降低了磁體成本,并逐步發(fā)展成為應(yīng)用最廣的稀土永磁材料,被廣泛應(yīng)用于電子通訊、電動(dòng)汽車、醫(yī)療設(shè)備、風(fēng)力發(fā)電等高新技術(shù)領(lǐng)域[3-4].進(jìn)入21世紀(jì),電動(dòng)/混動(dòng)汽車、風(fēng)力發(fā)電等低碳行業(yè)的迅速發(fā)展進(jìn)一步推動(dòng)了高性能永磁材料,特別是NdFeB永磁體的應(yīng)用[5-6].但同時(shí)也對(duì)NdFeB永磁材料的性能提出了更嚴(yán)格的要求,需要其具有更高的矯頑力(HC)和耐蝕性以滿足在復(fù)雜(高溫、高濕等)環(huán)境中的應(yīng)用[7-9].

HC是燒結(jié)NdFeB磁體最重要的磁性能參數(shù)之一.燒結(jié)磁體的HC主要由Nd2Fe14B主相及其晶粒邊界處的反磁化疇形核場(chǎng)所決定,形核場(chǎng)低,則磁體的HC就低.由于燒結(jié)NdFeB磁體主相晶界處的成分與晶粒內(nèi)部不一致以及晶界相分布不均等原因,引起磁體邊界層反磁疇形核場(chǎng)降低,導(dǎo)致磁體HC較低,溫度穩(wěn)定性較差,其磁性能會(huì)隨著溫度的升高急劇降低,影響其應(yīng)用[10].改善磁體溫度穩(wěn)定性的措施是提高其各向異性場(chǎng)(HA)及HC,通常是引入重稀土元素Dy[11].研究發(fā)現(xiàn),熔煉添加重稀土元素Dy,雖可在磁體主相晶粒外圍形成HA更高的(Nd,Dy)2Fe14B相,從而使磁體HC提高[12-13],但Dy同時(shí)也均勻地分布在主相Nd2Fe14B內(nèi)部.根據(jù)Durst等[14-17]提出的燒結(jié)NdFeB的HC機(jī)制可知,反磁化疇形核主要發(fā)生在主相Nd2Fe14B晶粒邊界的弱磁性區(qū),Dy的均勻分布導(dǎo)致重稀土元素添加量顯著增加(最高可達(dá)稀土總量的30%),不僅增加了生產(chǎn)成本且易引起磁稀釋效應(yīng)[18-19].

燒結(jié)NdFeB磁體主要由主相Nd2Fe14B、晶界富Nd相、少量富B相組成,其中,Nd是NdFeB磁體中最活潑的金屬元素,易與空氣中的氧和水發(fā)生反應(yīng),生成Nd2O3和H2[20].燒結(jié)NdFeB磁體抗蝕性較差的原因主要在于晶界富Nd相電極電位(約為-0.65 V)遠(yuǎn)低于主相Nd2Fe14B的電極電位(約為-0.515 V),易在磁體內(nèi)形成較大的電極電位差;且晶界富Nd相僅占磁體的10%～15%[21-23],含量遠(yuǎn)遠(yuǎn)低于主相,在高溫、高濕的腐蝕環(huán)境中,易形成具有小陽(yáng)極(富Nd相)大陰極(主相)特性的原電池[24-26],導(dǎo)致陽(yáng)極富Nd相的電流密度遠(yuǎn)大于陰極主相,加速了晶界富Nd相的腐蝕,致使主相Nd2Fe14B晶粒脫落,磁體磁性能急劇降低[27-28].

由此可見,NdFeB磁體的HC、耐蝕性與磁體晶界相成分及微觀結(jié)構(gòu)密切相關(guān).為提高磁體HC及耐蝕性,研究人員通過(guò)晶界添加非稀土金屬及合金化合物調(diào)控?zé)Y(jié)NdFeB磁體晶界相微觀結(jié)構(gòu),增強(qiáng)晶界富Nd相的穩(wěn)定性,提高晶界相電極電位、潤(rùn)濕性,促進(jìn)其均勻分布,加強(qiáng)晶界對(duì)主相的隔離能力.本文作者總結(jié)了近些年國(guó)內(nèi)外晶界添加非稀土金屬及合金化合物調(diào)控?zé)Y(jié)NdFeB磁體晶界相微觀結(jié)構(gòu)及其與磁體HC、抗蝕性等方面的部分研究成果,為制備高HC、高耐蝕性燒結(jié)NdFeB磁體提供參考.

1 非稀土金屬及合金化合物改善燒結(jié)磁體矯頑力

Knoch等[29]和Yan等[30]研究結(jié)果表明低熔點(diǎn)元素Al的晶界添加,使磁體HC由8.9 kOe提高到10.7 kOe,剩磁僅輕微降低.因?yàn)锳l元素易與磁體晶界富稀土相反應(yīng)生成Fe-Nd-O-Al新相,且新相中的Fe濃度小于初始磁體富稀土相(Fe-Nd-O)中的Fe濃度,具有較低的磁導(dǎo)率,減小了主相Nd2Fe14B間的磁交換耦合[31].此外,低熔點(diǎn)元素Al呈液相擴(kuò)散進(jìn)入晶界提高了主相-晶界相間的潤(rùn)濕性,促進(jìn)了晶界相的均勻分布[32].

Hu等[33-34]利用低壓等離子噴涂技術(shù)(LPPS)使Zn沿NdFeB晶界擴(kuò)散,通過(guò)透射電子顯微鏡(TEM)分析發(fā)現(xiàn)(圖1),Zn沿晶界擴(kuò)散使富稀土相中的Fe向外運(yùn)動(dòng)與Zn反應(yīng)生成Zn-Fe化合物.由于Fe向外擴(kuò)散的速率大于Zn向晶界相內(nèi)擴(kuò)散的速率,使富釹相中的釹濃度增高,提高了晶界相的去磁交換耦合作用[35-36].Zn在擴(kuò)散過(guò)程中輕微溶于主相Nd2Fe14B,可替代主相中Fe形成Nd-Fe-Zn化合物,被替代的Fe向晶界移動(dòng)繼續(xù)與Zn反應(yīng)形成Zn-Fe化合物,使晶界厚度增加(圖2).

圖1 Zn擴(kuò)散后樣品的TEM圖.N:晶界富Nd相;Φ:主相Nd2Fe14B;B1:Nd-Fe-Zn化合物;B2:Zn-Fe化合物[33]

圖2 Zn沿晶界擴(kuò)散示意圖.(a) 初始磁體;(b) Nd-Fe-Zn化合物形成;(c) Zn-Fe化合物形成[33]

Lin等[37]和Kianvas等[38]研究發(fā)現(xiàn),晶界添加Cu使燒結(jié)態(tài)NdFeB磁體HC下降,主要?dú)w因于游離態(tài)α-Fe和Nd2Fe17軟磁相的形成.但經(jīng)回火后,磁體中游離態(tài)α-Fe和Nd2Fe17軟磁相消失,晶界相分布均勻,表明合適的熱處理溫度可有效提高磁體晶界相的潤(rùn)濕性[39].根據(jù)Miedema公式[40]計(jì)算可知,Cu與Nd、Fe、B三種元素的混合焓(△Hmix)分別為-31 kJ/mol、+18 kJ/mol、+2 kJ/mol(+原子間相排斥、-原子間相結(jié)合).其中Cu與Nd的△Hmix最小,易與晶界富Nd相作用形成NdCu、NdCu2等新相,新相的形成有利于增強(qiáng)晶界相的釘扎能力,抑制主相晶粒長(zhǎng)大[41-42].

Kim等[43]和Fukagawa等[44]探究了不同Cu濃度對(duì)燒結(jié)磁體晶界相轉(zhuǎn)變溫度和微觀結(jié)構(gòu)的影響,發(fā)現(xiàn)隨著Cu濃度(原子百分?jǐn)?shù)為0.2%～0.5%)的增加磁體晶界相轉(zhuǎn)變溫度和HC降低.但經(jīng)790～850 ℃熱處理后,HC由28.7 kOe提高至29.4 kOe(原子百分?jǐn)?shù)為0.5% Cu),適宜的熱處理溫度使磁體主相間三叉交匯區(qū)的富稀土相由密排六方(hcp-Nd2O3)結(jié)構(gòu)轉(zhuǎn)變?yōu)镮a3空間群結(jié)構(gòu)(Ia-Nd2O3)(圖3),降低了主相-晶界相間的晶格畸變.

Cui等[45]探究了Ni對(duì)燒結(jié)NdFeB磁體晶界相結(jié)構(gòu)和成分的影響,發(fā)現(xiàn)晶界添加質(zhì)量百分?jǐn)?shù)為0.3%的Ni粉,磁體HC增加了12.3%.因?yàn)镹i的熔點(diǎn)(1 445 ℃)較高,Ni顆粒在主相表面富集并阻礙了主相晶粒的生長(zhǎng),使晶粒表面缺陷減少,降低了局部退磁場(chǎng),抑制了反磁化疇形核,磁體HC增加.通過(guò)掃描電子顯微鏡(SEM)進(jìn)一步分析發(fā)現(xiàn)(圖4),Ni的添加使晶界相分布更加均勻,晶界更加平直、光滑,減少了反磁化疇形核場(chǎng)所[46].

圖3 添加原子百分?jǐn)?shù)為0.5% Cu樣品的TEM圖.(a) 三叉區(qū)富Cu相;(b) 三叉區(qū)富Cu相高分辨透射電子顯微鏡(HRTEM)和電子衍射花樣(SADP)圖;(c) 晶界富Nd相HRTEM圖;(d)晶界富Nd相SADP圖[43]

圖4 含Ni質(zhì)量百分?jǐn)?shù)不同的樣品SEM圖.(a) 0% Ni;(b) 3% Ni;(c)是(b)中標(biāo)記線上Nd、Fe、Ni和O的分布圖[45]

Mural等[47]研究了高熔點(diǎn)化合物碳化鈦(TiC)對(duì)燒結(jié)磁體晶界相微觀結(jié)構(gòu)和HC的影響,TiC化學(xué)性質(zhì)穩(wěn)定,在燒結(jié)和熱處理過(guò)程中既不與富稀土相發(fā)生反應(yīng)也不溶于主相,而是以?shī)A雜物的形式存在于主相-晶界相間隙,起到細(xì)化主相晶粒、釘扎疇壁的作用[48-49].

Chen等[50]將質(zhì)量分?jǐn)?shù)為2%的氧化鎂(MgO)粉末與NdFeB磁粉球磨混合,經(jīng)擴(kuò)散處理后磁體HC由17.0 kOe增加到22.1 kOe.研究發(fā)現(xiàn),晶界添加的MgO與晶界富稀土相反應(yīng)生成Fe-Nd-O-Mg新相,新相的產(chǎn)生加強(qiáng)了晶界相對(duì)疇壁的釘扎效果,更有效地抑制磁疇反轉(zhuǎn).

Zhou等[51]利用磁控濺射工藝研究了MgO的擴(kuò)散對(duì)燒結(jié)NdFeB微觀結(jié)構(gòu)的影響,發(fā)現(xiàn)MgO的晶界擴(kuò)散使主相Nd2Fe14B晶粒邊緣突出的尖銳部分明顯減少,晶界相分布更加均勻,主相晶粒間普遍存在連續(xù)的薄帶狀晶界富稀土相(圖5),有效降低了磁體的退磁因子和主相間的磁交換耦合,并限制了主相晶粒的異常長(zhǎng)大,使磁體HC增加[52-53].

圖5 初始磁體表層SEM圖.(a) 磁體表層(b) 低倍SEM;(e) 表層背散射(BSE),MgO擴(kuò)散后磁體表層SEM圖:(c) 低倍SEM;(f) 高倍SEM;(d) 心部BSE圖[51]

2 非稀土金屬及合金化合物改善燒結(jié)磁體抗蝕性

Li等[54]研究了納米Mg粉的晶界添加對(duì)燒結(jié)磁體耐蝕性能的影響.發(fā)現(xiàn)隨著Mg含量的增加,磁體在質(zhì)量分?jǐn)?shù)為0.005% H2SO4(或3.5% NaCl)電解質(zhì)溶液中的腐蝕電位(Ecorr)由-0.652 V(-1.077 V)增加到-0.475 V(-0.847 V),腐蝕電流密度(icorr)由193.1 μA/cm2(54.03 μA/cm2)減小到46.5 μA/cm2(9.36 μA/cm2)(圖6),更高的Ecorr和更低的icorr表明磁體電化學(xué)穩(wěn)定性提高.利用SEM分析發(fā)現(xiàn),Mg與晶界富Nd相反應(yīng)生成化學(xué)性質(zhì)更穩(wěn)定的Mg-Nd新相,提高了晶間的電化學(xué)勢(shì)[55].

圖6 磁體的極化曲線.(a) 質(zhì)量分?jǐn)?shù)0.005% H2SO4溶液中;(b) 質(zhì)量分?jǐn)?shù)3.5% NaCl溶液中;(c) 磁體在H2SO4溶液中的腐蝕電位和腐蝕電流密度;(d) 磁體在NaCl溶液的腐蝕電位和腐蝕電流密度[54]

圖7 磁體磁性能與CuZn5粉末含量的關(guān)系[56]

Wang等[56]研究了晶界添加不同含量的CuZn5粉末對(duì)NdFeB燒結(jié)永磁體耐蝕性和HC的影響.發(fā)現(xiàn)隨著CuZn5含量的增加,磁體的剩磁(Br)、HC和最大磁能積(BH)max逐漸減少(圖7).

作者進(jìn)一步探究了不同添加量(質(zhì)量分?jǐn)?shù)為0%、3.5%、6%)的CuZn5合金對(duì)磁體抗蝕性的影響,發(fā)現(xiàn)隨著CuZn5合金含量的增加,磁體在體積分?jǐn)?shù)為0.1% H2SO4(或蒸餾水)電解質(zhì)溶液中的Ecorr由-722.43 V(-632.08 V)增加到-700.00 V(-594.92 V),icorr由457.09 μA/cm2(4.27 μA/cm2)減小到419.66 μA/cm2(3.63 μA/cm2)(圖8).晶界添加CuZn5合金使磁體具有更高的Ecorr和更低的icorr,是因?yàn)镃u、Zn均為低熔點(diǎn)元素在燒結(jié)和熱處理過(guò)程中沿晶界擴(kuò)散并與晶界富Nd相反應(yīng)形成Nd-M(M為Cu、Zn)相,降低了晶界相活性,提高了其電化學(xué)勢(shì),有效抑制了磁體的晶間腐蝕[57].

圖8 添加質(zhì)量分?jǐn)?shù)為0%、3.5%和6.0% CuZn5的燒結(jié)Nd-Fe-B磁體的極化曲線.(a) 蒸餾水;(b) 體積分?jǐn)?shù)為0.1% H2SO4溶液[56]

Pan等[58]研究了Cu/Zr共同添加對(duì)燒結(jié)磁體耐蝕性及HC的影響.發(fā)現(xiàn)添加質(zhì)量分?jǐn)?shù)為0.15% Cu和0.85% Zr使磁體HC由25.14 kOe提高到27.41 kOe(圖9),Ecorr由-0.799 V急劇增加到-0.697 V(圖10),磁體HC和耐蝕性能明顯提高.這可能是添加的低熔點(diǎn)金屬Cu與晶界富Nd相反應(yīng)生成含Cu富Nd相,減小了晶界相與主相間的極化電位差,抑制了磁體的晶界腐蝕.同時(shí)Cu/Zr的共添加也提高了主相-晶界相間的潤(rùn)濕性,使晶界變的更加平滑,加強(qiáng)了對(duì)主相的包裹能力,使磁體HC提高[59-60].

圖9 磁體的退磁曲線.(a) 初始磁體;(b) 添加質(zhì)量分?jǐn)?shù)為0.15% Cu和0.85% Zr的磁體;(c) 質(zhì)量分?jǐn)?shù)為1.0% Zr的磁體[58]

Zhang等[61]研究了Cu/Nb共同添加對(duì)燒結(jié)磁體耐蝕性的影響.發(fā)現(xiàn)添加質(zhì)量分?jǐn)?shù)為0.2% Cu和0.8% Nb的磁體,其Ecorr在質(zhì)量分?jǐn)?shù)為3.5% NaCl電解質(zhì)溶液中由-1.115 V增加到-0.799 V,icorr由62.33 μA/cm2減少到12.28 μA/cm2(圖11),抗腐蝕能力明顯提高.因?yàn)镹b的標(biāo)準(zhǔn)電極電位(-1.100 V)和Cu的標(biāo)準(zhǔn)電極電位(+0.337 V)均大于Nd的-2.431 V,減小了晶界富Nd相與主相間的電極電位差.

圖10 磁體在質(zhì)量分?jǐn)?shù)為2.5% NaCl水溶液中的極化曲線[58]

圖11 樣品在質(zhì)量分?jǐn)?shù)為3.5% NaCl溶液中的極化曲線[61]

進(jìn)一步通過(guò)SEM分析可知(圖12,13),Cu在晶界處富集并與晶界富Nd相反應(yīng)形成Nd-Cu新相,降低了晶界富Nd相的熔點(diǎn),促進(jìn)其沿晶界擴(kuò)散,分布更加均勻.而Nb進(jìn)入Nd2Fe14B主相,減少了主相和富Nd相的電位差,降低了腐蝕驅(qū)動(dòng)力.同時(shí)含Cu富Nd相和Nb-Fe相的形成降低了晶界富Nd相的體積分?jǐn)?shù),也有利于磁體耐蝕性的增加[62].

圖12 添加Cu、Nb后磁體的SEM圖.(a) 初始磁體;(b) 添加質(zhì)量分?jǐn)?shù)為0.2% Cu和0.8% Nb的磁體;(c) 添加質(zhì)量分?jǐn)?shù)1.0% Nb的磁體[61]

涂少軍等[63]研究發(fā)現(xiàn)晶界添加質(zhì)量分?jǐn)?shù)為0.1%納米氮化鋁(AlN)粉,可使燒結(jié)NdFeB磁體在質(zhì)量分?jǐn)?shù)3.5% NaCl電解質(zhì)溶液中的Ecorr由-0.673 V增加到-0.573 V,icorr由413 μA/cm2減少到222 μA/cm2(圖14).因?yàn)榫Ы缣砑覣lN有效阻礙了Nd2Fe14B主相晶粒的長(zhǎng)大,起到細(xì)化晶粒的作用,從而使晶界體積分?jǐn)?shù)增加,晶界富Nd相厚度降低,導(dǎo)致磁體的晶間腐蝕通道變窄[64],提高了磁體的耐蝕性.

圖13 圖7(b)畫線處的元素分布圖[61]

圖14 添加不同含量AlN磁體的極化曲線[63]

圖15 添加不同含量SiO2磁體的極化曲線[65]

Cui等[65]探究了晶界添加不同含量SiO2對(duì)燒結(jié)NdFeB磁體耐蝕性的影響.發(fā)現(xiàn)磁體在質(zhì)量分?jǐn)?shù)3.5% NaCl電解質(zhì)溶液中的極化曲線(圖15)隨著SiO2含量的增加,磁體Ecorr先增加后減小,而icorr先減小后增大,在添加質(zhì)量分?jǐn)?shù)為0.01% SiO2時(shí)達(dá)到最優(yōu),Ecorr和icorr分別為-0.595 V和279.6 μA/cm2(添加質(zhì)量分?jǐn)?shù)為0% SiO2時(shí),Ecorr和icorr分別為-0.676 V和700.6 μA/cm2),降低了磁體的腐蝕速率.SiO2的晶界添加有效優(yōu)化了富Nd晶界相的理化特性,提高了晶界富Nd相的化學(xué)穩(wěn)定性,且Si在擴(kuò)散過(guò)程中進(jìn)入富Nd相提高了其電極電位,使主相與晶界相間的電位差減小,有效降低了腐蝕驅(qū)動(dòng)力.

3 總 結(jié)

晶界相改性是提高燒結(jié)NdFeB磁體磁性能及耐蝕性的主要途徑.非稀土晶界添加物經(jīng)適宜的熱處理/擴(kuò)散處理后,可起優(yōu)化、修飾燒結(jié)NdFeB磁體晶界相組成、微觀結(jié)構(gòu)并改善其理化特性的作用,使磁體主相-晶界相間浸潤(rùn)性增加、晶格錯(cuò)配度降低,晶粒尺寸減小,晶界富Nd相電極電位及化學(xué)穩(wěn)定性提高,從而提高了磁體的HC及耐蝕性.

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ProgressofsinteredNdFeBpermanentmagnetsbythediffusionofnon-rareearthelementsandtheiralloycompounds

LyuMeng,KongTuo,ZhuMingyuan,HuYemin,JinHongming,LiWenxian*,LiYing*

(Laboratory for Microstructures,School of Materials Science and Engineering,Shanghai University,Shanghai 200072,China)

It has been found that the coercivity (HC) and corrosivity of sintered NdFeB magnets are closely related to the components and microstructure of their intergranular phase.The traditional smelting NdFeB magnets with adding heavy rare earth elements can modify intergranular phase to improve theHCand corrosion resistance of magnets.However,it makes the additives be homogenously distributed on the main phase,and causes magnetic decrease and cost increase.With the addition of non-rare earth materials into grain boundary,the microstructure of intergranular phase as well as its electrochemical potential and wettability can be optimized.As a result,the amount of heavy rare earth elements and cost of magnets could be reduced whilst theHCand corrosion resistance of magnets can be improved.This paper summarized the research on regulating the components and the microstructure of intergranular phase in sintered NdFeB magnets by non-rare earth metals and compounds,and its influence on coercivity and corrosion resistance.

sintered Nd-Fe-B magnets; grain boundary diffusion; coercivity; corrosion resistance; microstructure; non-rare earth metal and alloy compounds

10.3969/J.ISSN.1000-5137.2017.06.015

2017-09-29

國(guó)家自然科學(xué)基金委員會(huì)面上項(xiàng)目(51572166);上海高校特聘教授(東方學(xué)者)崗位計(jì)劃項(xiàng)目(TP2014041)

呂 蒙(1991-),男,博士研究生,主要從事磁性功能材料方面的研究.E-mail:lv1149879734@163.com

*通信作者: 李文獻(xiàn)(1977-),男,博士,教授,博士生導(dǎo)師,主要從事磁性材料和超導(dǎo)材料方面的研究.E-mail:shuliwx@shu.edu.cn;李 瑛(1962-),女,博士,教授,博士生導(dǎo)師,主要從事功能材料方面的研究.E-mail:liying62@shu.edu.cn

呂蒙,孔拓,朱明原,等.非稀土金屬及合金化合物改性燒結(jié)NdFeB磁體的研究進(jìn)展 [J].上海師范大學(xué)學(xué)報(bào)(自然科學(xué)版),2017,46(6):899-911.

formatLyu M,Kong T,Zhu M Y,et al.Progress of sintered NdFeB permanent magnets by the diffusion of non-rare earth elements and their alloy compounds [J].Journal of Shanghai Normal University(Natural Sciences),2017,46(6):899-911.

TM 273

A

1000-5137(2017)06-0899-13

郁 慧)