NdFeB自旋再取向相变的超声研究

研究了Nd_2Fe_(14)B中超声速度/衰减与自旋再取向的关系。计算了杨氏模量和泊松比,并发现它们在自旋再取向温度(T_(SR))附近出现畸变,说明在自旋再取向过程有软模出现。Nd_2Fe_(14)B自旋再取向相变是个渐变过程,有预相变现象。相变还与许多因素有关,如样品是各向同性还是各向异性,是磁化状态还是退磁状态,样品是处于升温状态还是降温状态,及特殊的样品处理过程,如经过高压处理等。     

淬速对Nd_9Fe_(70)Ti_3C_1Nb_3B_(14)快淬薄带晶化相变和磁性能的影响

采用不同的淬速(辊速Vs=10,15,20,25,30 m·s-1)制备了Nd_9Fe_(70)Ti_3C_1Nb_3B_(14)合金快淬薄带,并研究了薄带的晶化相变及其退火后的磁性能随快淬速度提高而发生的变化。结果表明:在淬速15和20 m·s-1之间有一个临界淬速,在临界淬速以下制备的低淬速薄带由非晶和少量Nd_2Fe_(14)B,Fe3B和α-Fe纳米晶组成,而在临界淬速以上制备的高淬速薄带由完全非晶构成。随着淬速的提高,薄带中非晶的热稳定性逐步提高。低淬速薄带晶化过程的相变为AP+Nd_2Fe_(14)B+Fe_3B+α-Fe→Nd_2Fe_(14)B+Fe_3B+α-Fe+Nd_3Fe_(20)B_2→Nd_2Fe_(14)B+Fe_3B+α-Fe,而高淬速薄带晶化过程的相变为AP→AP'+Nd_3Fe_(20)B_2→Fe_3B+Nd_3Fe_(20)B_2→Nd_2Fe_(14)B+Fe_3B+α-Fe。优化退火后,尽管不同淬速薄带的剩磁差别不大,但低淬速薄带的最佳矫顽力和磁能积分别比高淬速薄带的高28.41%和20.12%。     

SPS烧结双主相Nd_2Fe_(14)B-Ce_2Fe_(14)B稀土永磁材料微观结构的研究

研究了放电等离子烧结(SPS)技术制备的双主相Nd_2Fe_(14)B-Ce_2Fe_(14)B稀土永磁材料的微观结构。结果表明,使用SPS等离子烧结炉能够在较低烧结温度和较少保压时间下制备高密度的烧结双主相Nd_2Fe_(14)B-Ce_2Fe_(14)B稀土永磁材料,其微观组织是由独立的Nd_2Fe_(14)B相和Ce_2Fe_(14)B相均匀分布构成;退火能够使烧结后还未晶化的非晶体晶化,且SPS等离子烧结能够使烧结双主相Nd_2Fe_(14)B-Ce_2Fe_(14)B稀土永磁材料发生很少的稀土元素扩散。随着退火温度的升高,Nd_2Fe_(14)B相和Ce_2Fe_(14)B相之间稀土元素的扩散距离增大。     

添加La对NdFeB微观组织结构及快淬薄带磁性能的影响

研究了添加不同含量稀土La的Nd_(2.28)Fe_(13.58)B_(1.14)合金微观组织结构以及快淬薄带的磁性能。实验结果表明,添加La后,合金的物相组成仍为Nd_2Fe_(14)B相;随着La添加量的增加,Nd_2Fe_(14)B相的晶胞体积略有增大;合金快淬薄带的矫顽力与剩磁均下降,居里温度也随之降低。     

Nd-Fe-B三元相图

本工作通过对Nd-Fe-B三元合金样品退火态显微组织的观察,以及微区成分分析和物相鉴定,确定了Nd-Fe-B成分三角在室温下平衡相区的划分。采用差热分析测量了Nd-Fe-B合金的相变点,绘制了Nd=11.76at。％、B≤44.56at。％和B=5.88at。％、Nd≤45.41at。％两个三元垂直剖面相图。这两个剖面相交于Nd_2Fe_(14)B化合物相的正分点,因此,专门讨论了Nd_2Fe_(14)B合金的热分析曲线,结果发现:Nd_2Fe_(14)B合金从液态冷却凝固时,Nd_2Fe_(14)B相的析出是经包晶反应完成的,该合金的铸态形貌也充分说明了这一点。     

NdFeB/SmCo_5复合永磁体界面反应规律研究

对NdFeB/SmCo_5复合永磁体界面反应可能生成的合金相及其形成能力进行了分析,以控制NdFeB和SmCo_5两硬磁相间的界面反应,有效改善复合磁体的磁性能。利用Miedema理论和几何外推模型,计算了NdFeB/SmCo_5复合体系可能反应生成的系列合金相的形成焓,分析了2∶14∶1和1∶5两硬磁合金相的元素替代规律,得出了NdFeB与SmCo_5间的界面反应热力学规律。结果表明:2∶14∶1和1∶5合金相的形成焓随稀土元素改变而变化,且1∶5合金相的形成焓更负;SmCo_5合金相较Nd2Fe14B合金相更稳定,但是稀土含量为33.3%的SmCo_2合金相的形成焓更负,其形成能力优于SmCo_5合金相;Nd(或Pr)或Fe取代SmCo_5合金相中的Sm或Co后增大了其形成焓,降低了1∶5相的形成能力;然而,Sm或Co取代Nd_2Fe_(14)B合金相中的Nd或Fe反而使2∶14∶1相的形成焓更负,增强了其形成能力。Nd_2Fe_(14)B合金相转变成Nd_2Co_(14)B合金相的热力学驱动力要显著高于其转变成Sm_2Fe_(14)B合金相的,使得Nd_2Fe_(14)B合金相优先发生界面反应形成Nd_2(Fe,Co)_(14)B合金相,而SmCo_5合金相则倾向于形成更稳定的SmCo_2合金相。     

R_2Co_(14)B和Nd_2(Fe_(1-x)Co_x)_(14)B单晶的磁化强度与磁晶各向异性

测定了R_2Co_(14)B(R为La、Nd和Gd)和Nd_2(Fe_(1-x)Cox)_(14)B单晶试样的磁化强度和各向异性场。La_2Co_(14)B室温下的易磁化方向是[110],其中Co的亚晶格具有易面各向异性,4.2K时,K_1=-1.30MJ/m~3。稀土离子在R_2Co_(14)B中的交换场比在R_2Fe_(14)B中要小,这就导致了稀土亚晶格的磁化强度和各向异性场随温度升高而迅速下降。由于Co的易面各向异性及R—Co的交换效应较R—Fe弱,这就导致在300K～500K温度范围内,Nd_2(Fe_(1-x)Cox)_(14)B的各向异性场变得几乎与Co的浓度无关。     

轻稀土Ce对Nd-Fe-B永磁材料的结构与磁性能影响

轻稀土铈替代稀土永磁材料钕铁硼中的钕是降低生产成本、平衡稀土资源利用比较有效的方式。本文首先通过调节合金成分研究了制备Nd_2Fe_(14)B单相的工艺,其次以轻稀土铈部分替代钕的方式通过X射线衍射仪、扫描电镜及振动样品磁强计分别研究了(Nd_(1-x)Ce_x)_(11.76)Fe_(81.39)B_(6.85)(x=0.0,0.1,0.2)物相的晶体结构、微观组织及磁性能。研究结果表明替代后的物相均为Nd_2Fe_(14)B型的四方相。通过在600℃下烧结2小时,随着铈添加的含量增多合金的内禀矫顽力以及剩磁虽然有所下降,但当铈含量添加到20%(x=0.2)时,合金的内禀矫顽力和剩磁仍然可达到9.31kOe和98.80emu/g。     

NdFeB永磁合金物相检验及分析方法的研究

采用普通金相,彩色金相,电子探针,电镜及x射线衍射等方法确定,NdFeB永磁合金中的物相主要为Nd_2Fe_(14)B、富Nd相及富B相。发现在普通条件下,只有富Nd相有吸附磁粉作用,且易氧化。基体相Nd_2Fe_(14)B是NdFeB永磁合金磁能积的主要影响因素,而富B相和基体相是影响矫顽力iHc的主要物相。     

边界结构改性对烧结钕铁硼矫顽力的影响

对边界结构改性对磁体的显微组织结构和磁性能以及温度特性的影响进行了研究。设计了第一主相磁粉合金成分Nd_(24)Pr_6Co_(1.8)Fe_(61.1)Nb_(0.6)Al_(0.30)Cu_(0.2)B_(1.0),第二边界区结构合金成分Dy_(30)Fe_(68.2)Nb_(0.6)Al_(0.3)Cu_(0.2)B_(1.0),第三晶界相合金成分Nd_(40)Pr_(10)Fe_(47)Cu_(2.0)B_(1.0)。发现边界结构改性可以在基本不影响或者很小影响剩磁的前提下大幅度提高矫顽力。边界结构改性工艺主要是使重稀土元素Dy通过晶界扩散进入到Nd2Fe14B主相晶粒边界区而不是晶粒芯部,在Nd_2Fe_(14)B主相晶粒边界区形成具有高磁晶各向异性场的(Nd,Dy)_2Fe_(14)B壳层结构,从而达到大幅度提高矫顽力的目的。     

Nucleation undercooling,solidification structures and magnetic properties of Nd_9Fe_(85–x)Ti_4C_2B_x (x=10–15) magnetic alloys

Nd_9Fe_(85–x)Ti_4C_2B_x(x=10–15) magnetic alloys were investigated by differential thermal analysis and X-ray diffraction analysis. The results showed that with the B content increasing from 10 at.% to 15 at.%, the liquidus temperatures TL of the alloys decreased from 1498.5 to 1472.5 K; the solidus temperatures TS of them increased from 1353.2 to 1358.3 K; and the nucleation undercooling of the alloy melts cooled at the rate of 40 K/min decreased from 122.8 to 95.9 K, resulting in the solidification structures consisting of Nd_2Fe_(14)B, Fe_3B, α-Fe, Nd1.1Fe4B4 and TiC nanocrystallines. Furthermore, the Nd_9Fe_(85–x)Ti_4C_2B_x(x=11, 13, 15) bulk alloys in sheet form with the thickness of 0.7 mm were prepared by copper mold suction casting and their solidification characteristics and solidification structures under sub-rapidly cooling rate were investigated. The results showed that partially amorphous structures were obtained in the as-cast bulk alloys and the amount of amorphous decreased with the increase of the B content. By annealing the as-cast bulk alloys at 923 K for 10 min, the nanocomposite microstructures composed with Nd_2Fe_(14)B, Fe_3B and α-Fe nanocrystallines, which showed a single-phase hard magnetic behavior and enhanced magnetic properties, were achieved.     

（Nd,Pr）2Fe12Co2B化合物的磁性

利用脉冲强磁场、磁天平及交流初始磁化率测量仪研究了(Nd_(1-x)Pr_x)_2Fe_(12)Co_2B系列化合物的基础磁性。结果表明:(Nd_(1-x)Pr_x)_2Fe_(12)Co_2B化合物具有比NdFe_(14)B更大的单轴磁晶各向异性区。镨代替钕在300～500K时对磁化强度及磁晶各向异性的影响很小。以钕、镨混合稀土并以少量钴部分取代铁的(Nd, Pr)-(Fe_2, Co)-B磁体不仅成本降低,而且为该磁体的低温应用提供了更大的单轴磁晶各向异性区。     

磁控溅射表面镀膜对Nd_2Fe_(14)B稀土永磁体抗腐蚀性能的影响

在Nd_2Fe_(14)B稀土永磁体基体表面,采用磁控溅射(直流+射频)技术制备了Ti/Ni,Ti/Al和Al/Ni等二元合金薄膜和Ti/Al/Ni三元合金薄膜。并通过中性盐雾试验、腐蚀失重计算、电化学腐蚀试验、金相观察等方式,对比研究了不同表面处理对Nd_2Fe_(14)B稀土永磁体基体抗腐蚀性能的影响,并构建了腐蚀模型。研究发现:Ti/Ni,Ti/Al和Al/Ni等二元合金薄膜和Ti/Al/Ni三元合金薄膜均有效地提高了Nd_2Fe_(14)B稀土永磁体基体耐中性盐雾腐蚀和电化学腐蚀的能力;Ti/Al/Ni三元合金薄膜较Ti/Ni,Ti/Al和Al/Ni等二元合金薄膜有更优良的综合耐腐蚀性能,其磁控溅射工艺参数为:Ar流量60 sccm,基片温度常温,Ni,Al,Ti的溅射功率都为250 W,基片转速20 r·min~(-1),镀膜均速0.3 nm·s~(-1),总计溅射时间1 h。     

Nd_(15).Fe_(78.4)B_(5.8)取向磁体的自旋再取向的声波研究

在100～300 K温区内,用30 MHz频率的超声对Nd_(15.8)Fe_(18.4)B_(5.8)磁体进行了纵波和横波的声速及声衰减测量。发现对应于自旋再取向温度、声速及声波衰减均发生突变,其转变温度为132 K。从自由能角度,在理论上阐述了声波与发生自旋再取向的关系。发现自旋间交换能的变化,对自旋再取向起着关键作用。由超声波衰减变化的振荡特性,推知自旋偏转的量子性,即每个自旋偏转的数值和偏转了的自旋数目并不是温度的连续函数。自旋再取向具有持续性。     

Ho对烧结钕铁硼永磁体性能的影响

在工业生产线上制备了合金成分为(Pr-Nd)_(28.8-x)D_(y2)Ho_xFebalNb_(0.2)B_(1.05)的烧结钕铁硼永磁体,研究了Ho取代部分金属Pr-Nd对烧结钕铁硼永磁体磁性能、显微组织以及耐腐蚀性能的影响。研究结果表明,Ho取代部分金属Pr-Nd可促进合金片中Nd_2Fe_(14)B柱状晶的生长,使富Nd相以薄片状更均匀地分布于Nd_2Fe_(14)B主相晶粒之间,并使永磁体的显微组织致密化,从而有效提高其内禀矫顽力(但剩磁降低)及耐腐蚀性能,减少失重。当Ho添加量为3%时,产品表现出最好的综合性能,剩磁(Br)达到1.237T,内禀矫顽力(H_(cj))达到1.76 MA/m,J-H退磁曲线方形度(H_k/H_(cj))为0.99。     

Magnetic properties and microstructure of Fe_(69.5-x)Nd_7B_(21)Nb_(2.5)Ga_x(x=0-1)alloys

The Fe_(69.5-x)Nd_7 B_(21)Nb_(2.5)Ga_x(x = 0-1)permanent magnets in the form of rods were prepared by annealing the bulk amorphous alloys.The magnetic properties,phase evolution and microstructure of the alloys were investigated systematically.It is found that the glass forming ability(GFA), microstructure and magnetic properties are sensitive to Ga content for Fe_(69.5-x)Nd_7 B_(21)Nb_(2.5)Ga_x(x = 0-1)bulk alloys.The annealed alloys are mainly composed of soft α-Fe,hard Nd_2 Fe_(14)B and nonmagnetic Nd_(1.1)Fe_4 B_4 phases.When x = 0.3,the optimally annealed magnets exhibit magnetic properties of the remanence Br = 0.63 T,intrinsic coercivity H_(cj) = 368.68 kA/m and maximum energy product(BH)_(max) = 33.73 kJ/m~3.Furthermore,magnetic field heat treatment at the temperature close to Curie temperature of Nd_2 Fe_(14)B phase was applied to the annealed Fe_(69.2)Nd_7 B_(21)Nb_(2.5)Ga_(0.3) magnet.The results of X-ray diffraction(XRD)and transmission electron microscopy(TEM)indicate that the magnetic field heat treatment can be beneficial for the precipitation of α-Fe.Thus,the B_r,H_(cj) and(BH)_(max) are enhanced by 8.7%,6.3% and 16.3%,respectively.     

粘结磁性材料的制备方法

日本三菱材料公司制取粘结磁性材料的方法为:将NdFeB系合金铸锭置于真空度为10~(-6)乇的真空炉中,通入氢气,并升温至约700℃。合金被氢化后变脆,于800～900℃分解成NdH_2、αFe和Fe_2B。再于10~(-6)乇真空中加热800～900℃脱氢,得到Nd_(?)Fe_(14)B的异向性磁性材料粉末,粉末颗粒直径为0.3～0.2μm。     

AN ISOBAR-ISOTHERMAL PHASE DIAGRAM OF THE Nd-Fe-B SYSTEM AT ATMOSPHERIC PRESSURE AND 1000℃

An isothermal section of Nd-Fe-B system at 1000℃ and the phase equilibrium relationship in Fe-Ndand Nd-B binary systems were investigated with diffusion couple by means of metallographic observation,electron microprobe analysis and X-ray diffraction.It was shown that there are three stable ternary com-pounds,Nd_2Fe_(14)B,Nd_2Fe_7B_6 and Nd_9Fe_3B_8 in Nd-Fe-B system at 1000℃.None of these phases has solu-bility,that is,they are exactly stoichiometric phases.On the other hand,there exist rather wide two-phaseregions between Nd_2Fe_7B_6 and liquid as well as between Nd_9Fe_3B_8 and liquid.It was identified that there isno NdFe_2 compound in the system under atmospheric pressure.     

Crystal structure and phase relations of Pr_2Fe_(14)B-La_2Fe_(14)B system

The crystal structure and phase relations of the Pr_2Fe_(14)B-La_2Fe_(14) B system were investigated by X-ray powder diffraction(XRD), differential scanning calorimetry(DSC) and scanning electron microscopy(SEM) equipped with energy dispersive X-ray spectroscopy(EDS). The crystal structure parameters were determined by full-profile Rietveld refinements. The results revealed that all alloys of(Pr_(1–x)La_x)_2Fe_(14)B crystallized the Nd_2Fe_(14)B-type structure with the space group P4_2/mnm and formed a continuous solid solutions between x=0.0 and 1.0. The lattice parameter a, c, unit-cell volume V and c/a ratio increased linearly with the La concentration. Determined by thermogravimetry analysis, the Curie temperature(T_C), phase transition temperature and melting temperature of(Pr_(1–x)La_x)_2Fe_(14)B decreased linearly upon the La content. Based on the results of DSC measurements and X-ray powder diffraction examinations, the phase diagram of the Pr_2Fe_(14)B-La_2Fe_(14) B system was built up.     

The microstructure and magnetization reversal behavior of melt-spun (Nd1−xCex)-Fe-B ribbons

In this study,the alloy ingots with nominal compositions of(Nd_(1-x)Ce_x)_(31)Fe_(bal)Co_(0.2)Ga_(0.1)B(x=0, 0.1 wt%,0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%) were prepared and then melt-spun to form nanocrystalline ribbons at the wheel speed of 20 m/s. XRD results show that all melt-spun ribbons exhibit the tetragonal structure(Nd,Ce)_2 Fe_(14)B phase with the space group P42/mmm. The Curie temperature and lattice constant decrease with the increase of Ce content. The Curie temperature decreases gradually from 306 to 247 ℃with the increase of Ce content. Those results indicate that Ce element has been incorporated into Nd_2 Fe_(14)B main crystalline phase and formed(Ce,Nd)-Fe-B hard magnetic phase. It is also found that the remanence ratio(M_r/M_s) decreases from 0.693 to 0.663 and the coercivity(H_c) decreases from 18.7 to14.2 kOe with the increase of Ce content. However, a relatively high coercivity of 18.3 kOe for(Nd_(1-x)Ce_x)_(31)Fe_(bal)Co_(0.2)Ga_(0.1)B(x = 0.2) melt-spun ribbon is achieved. The coercivity is sensitive to microstructure. The AFM patterns show the sample(x = 0.2) has the most uniform and finest microstructure. The magnetization reversal behavior(δM plots) is discussed in detail. The positive δM value is observed in every sample, which confirms the existence of exchange coupling interaction. Evidently, theδM maximum value reaches 0.9 in the sample(x = 0.2). It is indicated that the intergranular exchange coupling effect is the strongest, which is consistent with coercivity enhancing.