釹鐵硼晶界重構(gòu)與高抗蝕性磁體制備研究
發(fā)布時間：2018-09-08 15:09
【摘要】：Nd-Fe-B磁體因其優(yōu)異的磁性能被稱為“磁王”,是應(yīng)用最廣泛的稀土功能材料,已成為高新技術(shù)的關(guān)鍵基礎(chǔ)材料。但是,燒結(jié)Nd-Fe-B磁體的晶界富Nd相與硬磁性Nd2Fe14B主相的電位差巨大,導(dǎo)致磁體抗腐蝕性能極差,是目前該領(lǐng)域亟待解決的重要問題。本文針對這一組織結(jié)構(gòu)根源,基于晶界重構(gòu)思路,設(shè)計與合成了Nd64Co36、Nd65Ni35和Nd30Co65Cu5(Nd6Co13Cu)等系列高電位輔合金；采用雙合金工藝制備出晶界相電極電位與主相相當(dāng)?shù)男麓朋w,有效降低兩相間電化學(xué)反應(yīng)的驅(qū)動力,顯著提高了磁體的本征抗蝕性。此外,采用Ta或Nb等高熔點金屬進(jìn)行晶界改性,可以抑制主相晶粒異常長大,進(jìn)一步提高磁體的磁性能,尤其是矯頑力。主要結(jié)果如下：根據(jù)合金相圖與元素理化特性參數(shù),設(shè)計并合成了Nd64Co36、Nd65Ni35和 Nd6Co13Cu等與主相潤濕性良好的低熔點高電位輔合金,進(jìn)行釹鐵硼磁體晶界組織重構(gòu)。Nd64Co36、Nd65Ni35和Nd6Co13Cu重構(gòu)晶界合金的熔點分別為566℃、540℃和605℃,低于富Nd相的熔化溫度655℃。在燒結(jié)過程中先于富Nd相熔化成液態(tài),改善晶界相的流動性和與主相的潤濕性,提高了磁體的燒結(jié)密度。合金中的Co、Ni和Cu的標(biāo)準(zhǔn)電極電位分別是-0.277 V、-0.250 V和+0.337 V,遠(yuǎn)高于Nd(-2.431V)和Fe(-0.440 V),進(jìn)入晶界相后可提高電極電位。此外,Co、Ni、Cu 在晶界處形成化學(xué)性質(zhì)更加穩(wěn)定的化合物,阻礙腐蝕沿晶界的擴(kuò)展。由于重構(gòu)磁體主合金成分非常接近Nd2Fe14B正比相,磁體的總稀土用量可降至28.00 wt.%(僅比正比相高1.33 wt%,遠(yuǎn)低于商業(yè)磁體30.5 wt%的稀土含量),減少了磁體中富Nd相的體積分?jǐn)?shù),有效提高燒結(jié)磁體的抗腐蝕性能,并節(jié)約了寶貴的稀土資源,大幅降低成本。通過燒結(jié)后續(xù)熱處理,重構(gòu)的晶界相沿主相晶粒光滑連續(xù)分布,消除相鄰鐵磁相晶粒間的磁耦合作用,提高磁體的磁性能,尤其是矯頑力�；陔p合金工藝,利用上述三種高電位輔合金和近2：14：1正比相的主合金進(jìn)行晶界重構(gòu), 制備出系列高本征抗蝕性Nd-Fe-B燒結(jié)磁體。采用(Pr,Nd)12.97Fe80.58Ga0.19B6.26主合金添加0.5 wt.%的Nd64C036輔合金,重構(gòu)后的磁體綜合性能最佳,Br、Hcj和(BH)max分別達(dá)到13.99 kGs、13.01 kOe和47.93 MGOe,總稀土含量僅為29.26 wt.%,遠(yuǎn)低于磁性能相當(dāng)?shù)腘48商用磁體。且該磁體在不同腐蝕環(huán)境中都具有更好的本征抗蝕性,在3.5%NaC1溶液中的腐蝕電位為-0.779 V,遠(yuǎn)高于-1.032 V(N48)；在120℃、2個大氣壓和100%相對濕度環(huán)境下96小時的失重量也從2.47mg/cm2下降到0.3mg/cm2;在0.1 M硫酸溶液中1800秒的放氫量從62 ml下降到35ml。采用Nd65Ni35輔合金進(jìn)行晶界重構(gòu)也能提高磁體的本征抗蝕性,其最佳添加量為2wt.%。在此基礎(chǔ)上,對稀土含量更低的(Pr,Nd)12.44Fe81.45B6.11磁體進(jìn)行Nd6Co13Cu三元合金晶界重構(gòu)。添加量為2wt.%的重構(gòu)磁體稀土總量僅為28.46wt.%,富Nd相體積分?jǐn)?shù)大幅降低。此外,由于標(biāo)準(zhǔn)電極電位更高的Cu元素的引入,進(jìn)一步提高了晶界相的穩(wěn)定性。該磁體在3.5% NaCl溶液中的腐蝕電位提高到-0.705V,在濕熱環(huán)境下96小時的失重量進(jìn)一步降低至0.28 mg/cm2;在0.1 MH2SO4溶液中浸蝕1800秒的放氫量也降低至18.52 ml。同時,該磁體仍具有較高的磁性能,其Br、Hcj和(BH)max分別達(dá)到14.03kGs、12.62 kOe和48.55 MGOe。基于高熔點金屬Ta或Nb進(jìn)行晶界改性,在提高本征抗蝕性的同時,可以有效抑制主相晶粒異常長大,進(jìn)一步提高磁體的矯頑力。與商用磁體相比,單獨采用Ta進(jìn)行晶界重構(gòu),主相晶粒尺寸由22.4μm細(xì)化到8.7μm,磁體矯頑力由16.7 kOe提高至17.7 kOe,濕熱環(huán)境下96h的失重量由2.47 mg/cm2下降到0.23 mg/cm2。采用Nb和高電位Cu晶界改性,不僅有效細(xì)化晶粒尺寸提高矯頑力,更重要的是低熔點高電位元素Cu的共同添加,可以進(jìn)一步提高晶界電位以及主相與晶界相的潤濕性,提高磁體的本征抗蝕性。實驗證明,磁體在濕熱環(huán)境下96h的失重量僅為未改性磁體的1/5；在3.5%NaCl溶液中的腐蝕電位也由-1.115 V提高到-0.799 V,腐蝕電流由62.33μA/cm2降低到12.28μA/cm2。
[Abstract]:Nd-Fe-B magnet is called "magnet king" because of its excellent magnetic properties, which is the most widely used rare earth functional material and has become the key basic material of high and new technology. However, the potential difference between the Nd-rich phase at grain boundary of sintered Nd-Fe-B magnet and the main phase of hard magnetic Nd_2Fe_14B is huge, resulting in the extremely poor corrosion resistance of the magnet, which is an urgent problem to be solved in this field. In this paper, a series of high potential auxiliary alloys Nd64Co36, Nd65Ni35 and Nd30Co65Cu5 (Nd6Co13Cu) were designed and synthesized based on the idea of grain boundary reconstruction, and a new magnet with a grain boundary electrode potential equivalent to the main phase was prepared by double alloy process, which can effectively reduce the driving force of electrochemical reaction between two phases. The intrinsic corrosion resistance of the magnet is improved. In addition, the abnormal grain growth of the main phase can be restrained and the magnetic properties, especially the coercivity, can be further improved by grain boundary modification with high melting point metals such as Ta or Nb. The melting points of Nd64Co36, Nd65Ni35 and Nd6Co13Cu reconstructed grain boundary alloys are 566, 540 and 605, respectively, which are lower than the melting temperatures of Nd-rich phase 655 C. During the sintering process, the Nd-rich phase melts into liquid state before the Nd-rich phase melts, improving the fluidity of grain boundary phase and improving the fluidity of grain boundary phase. The standard electrode potentials of Co, Ni and Cu in the alloy are - 0.277 V, - 0.250 V and + 0.337 V, much higher than those of Nd (- 2.431 V) and Fe (- 0.440 V), respectively. The electrode potentials can be increased after entering the grain boundary phase. The total rare earth content of the reconstructed magnet can be reduced to 28.00 wt. (only 1.33 wt% higher than the proportional phase and much lower than 30.5 wt% of the commercial magnet). The volume fraction of the Nd-rich phase in the reconstructed magnet is reduced, the corrosion resistance of the sintered magnet is improved effectively, and the precious metal is saved. After heat treatment, the reconstructed grain boundary phases are smoothly and continuously distributed along the main phase grains, eliminating the magnetic coupling between adjacent ferromagnetic grains and improving the magnetic properties, especially the coercivity of the magnets. A series of Nd-Fe-B sintered magnets with high intrinsic corrosion resistance were fabricated by grain boundary reconstruction of Au. By adding 0.5 wt.% Nd64C036 auxiliary alloy into (Pr, Nd) 12.97 Fe 80.58 Ga 0.19 B 6.26 main alloy, the comprehensive properties of the reconstructed magnets were the best. Br, Hcj and (BH) Max reached 13.99 kGs, 13.01 kOe and 47.93 MGOe, respectively. The total rare earth content was only 29.26 wt.%, much lower than that of the magnets. The corrosion potential of N48 commercial magnet in 3.5% NaC1 solution is - 0.779 V, which is much higher than - 1.032 V (N48). The weight loss of N48 commercial magnet in 96 hours is also reduced from 2.47 mg/cm2 to 0.3 mg/cm2 at 120 C, 2 atmospheric pressures and 100% relative humidity, and in 0.1 M sulfuric acid solution. The intrinsic corrosion resistance of Nd65Ni35 auxiliary alloy can also be improved by introducing the Nd65Ni35 auxiliary alloy for grain boundary reconstruction. The optimum addition of Nd65Ni35 auxiliary alloy is 2wt. The corrosion potential of the magnet in 3.5% NaCl solution was increased to - 0.705V, and the weight loss was further reduced to 0.28 mg/cm2 in 96 hours under humid and hot conditions, and dissolved in 0.1 MH2SO4. At the same time, the magnetic properties of the magnet are still high. The Br, Hcj and (BH) max of the magnet reach 14.03 kGs, 12.62 kOe and 48.55 MGOe respectively. The modification of grain boundary based on the high melting point metal Ta or Nb can effectively restrain the abnormal grain growth of the main phase and further improve the intrinsic corrosion resistance. Comparing with commercial magnets, the grain size of main phase was refined from 22.4 to 8.7 micron, the coercivity of magnets was increased from 16.7 kOe to 17.7 kOe, and the weight loss was reduced from 2.47 mg/cm2 to 0.23 mg/cm2 in 96 h under hot and humid conditions. The intrinsic corrosion resistance of the magnet can be further improved by the co-addition of low melting point and high potential element Cu, which can further improve the grain boundary potential and the wettability of the main phase and grain boundary phase. Increased to -0.799 V, the corrosion current decreased from 62.33 A/cm2 to 12.28 A/cm2.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TM27
本文編號：2230879
[Abstract]:Nd-Fe-B magnet is called "magnet king" because of its excellent magnetic properties, which is the most widely used rare earth functional material and has become the key basic material of high and new technology. However, the potential difference between the Nd-rich phase at grain boundary of sintered Nd-Fe-B magnet and the main phase of hard magnetic Nd_2Fe_14B is huge, resulting in the extremely poor corrosion resistance of the magnet, which is an urgent problem to be solved in this field. In this paper, a series of high potential auxiliary alloys Nd64Co36, Nd65Ni35 and Nd30Co65Cu5 (Nd6Co13Cu) were designed and synthesized based on the idea of grain boundary reconstruction, and a new magnet with a grain boundary electrode potential equivalent to the main phase was prepared by double alloy process, which can effectively reduce the driving force of electrochemical reaction between two phases. The intrinsic corrosion resistance of the magnet is improved. In addition, the abnormal grain growth of the main phase can be restrained and the magnetic properties, especially the coercivity, can be further improved by grain boundary modification with high melting point metals such as Ta or Nb. The melting points of Nd64Co36, Nd65Ni35 and Nd6Co13Cu reconstructed grain boundary alloys are 566, 540 and 605, respectively, which are lower than the melting temperatures of Nd-rich phase 655 C. During the sintering process, the Nd-rich phase melts into liquid state before the Nd-rich phase melts, improving the fluidity of grain boundary phase and improving the fluidity of grain boundary phase. The standard electrode potentials of Co, Ni and Cu in the alloy are - 0.277 V, - 0.250 V and + 0.337 V, much higher than those of Nd (- 2.431 V) and Fe (- 0.440 V), respectively. The electrode potentials can be increased after entering the grain boundary phase. The total rare earth content of the reconstructed magnet can be reduced to 28.00 wt. (only 1.33 wt% higher than the proportional phase and much lower than 30.5 wt% of the commercial magnet). The volume fraction of the Nd-rich phase in the reconstructed magnet is reduced, the corrosion resistance of the sintered magnet is improved effectively, and the precious metal is saved. After heat treatment, the reconstructed grain boundary phases are smoothly and continuously distributed along the main phase grains, eliminating the magnetic coupling between adjacent ferromagnetic grains and improving the magnetic properties, especially the coercivity of the magnets. A series of Nd-Fe-B sintered magnets with high intrinsic corrosion resistance were fabricated by grain boundary reconstruction of Au. By adding 0.5 wt.% Nd64C036 auxiliary alloy into (Pr, Nd) 12.97 Fe 80.58 Ga 0.19 B 6.26 main alloy, the comprehensive properties of the reconstructed magnets were the best. Br, Hcj and (BH) Max reached 13.99 kGs, 13.01 kOe and 47.93 MGOe, respectively. The total rare earth content was only 29.26 wt.%, much lower than that of the magnets. The corrosion potential of N48 commercial magnet in 3.5% NaC1 solution is - 0.779 V, which is much higher than - 1.032 V (N48). The weight loss of N48 commercial magnet in 96 hours is also reduced from 2.47 mg/cm2 to 0.3 mg/cm2 at 120 C, 2 atmospheric pressures and 100% relative humidity, and in 0.1 M sulfuric acid solution. The intrinsic corrosion resistance of Nd65Ni35 auxiliary alloy can also be improved by introducing the Nd65Ni35 auxiliary alloy for grain boundary reconstruction. The optimum addition of Nd65Ni35 auxiliary alloy is 2wt. The corrosion potential of the magnet in 3.5% NaCl solution was increased to - 0.705V, and the weight loss was further reduced to 0.28 mg/cm2 in 96 hours under humid and hot conditions, and dissolved in 0.1 MH2SO4. At the same time, the magnetic properties of the magnet are still high. The Br, Hcj and (BH) max of the magnet reach 14.03 kGs, 12.62 kOe and 48.55 MGOe respectively. The modification of grain boundary based on the high melting point metal Ta or Nb can effectively restrain the abnormal grain growth of the main phase and further improve the intrinsic corrosion resistance. Comparing with commercial magnets, the grain size of main phase was refined from 22.4 to 8.7 micron, the coercivity of magnets was increased from 16.7 kOe to 17.7 kOe, and the weight loss was reduced from 2.47 mg/cm2 to 0.23 mg/cm2 in 96 h under hot and humid conditions. The intrinsic corrosion resistance of the magnet can be further improved by the co-addition of low melting point and high potential element Cu, which can further improve the grain boundary potential and the wettability of the main phase and grain boundary phase. Increased to -0.799 V, the corrosion current decreased from 62.33 A/cm2 to 12.28 A/cm2.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TM27
【參考文獻(xiàn)】
相關(guān)期刊論文 前3條
1 宋振綸;李衛(wèi);;釹鐵硼永磁材料表面防護(hù)技術(shù):特點·應(yīng)用·問題[J];磁性材料及器件;2008年01期
2 成問好,李衛(wèi),李傳健;添加Nb對Nd-Fe-B磁體溫度穩(wěn)定性的影響[J];金屬學(xué)報;2001年01期
3 鄭精武;姜力強(qiáng);陳巧玲;;Electrochemical Corrosion Behavior of Nd-Fe-B Sintered Magnets in Different Acid Solutions[J];Journal of Rare Earths;2006年02期
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