烧结Nd-Fe-B永磁合金矫顽力机制的理论与实验研究

从理论和实验上研究了烧结Ｎｄ－Ｆｅ－Ｂ永磁合金的矫顽力随取向磁场的变化规律。指出磁体反磁化过程主要是晶粒边界软磁性区的反磁化成核以及反磁化核长大成畴并向晶粒内部不可逆畴壁位移的过程。比较了成核场与退钉扎场的大小及其随磁场方向的变化，并得出结论：退钉扎场是决定烧结Ｎｄ－Ｆｅ－Ｂ磁体矫顽力的主要机制。 关键词：     

Coercivity enhancement of sintered Nd-Fe-B magnets by grain boundary diffusion with Pr80-xAlxCu20 alloys

A grain boundary diffusion (GBD) process with Pr_80-xAl_xCu₂₀ (x = 0, 10, 15, 20) low melting point alloys was applied to commercial 42M sintered Nd-Fe-B magnets. The best coercivity enhancement of a diffused magnet was for the Pr₆₅Al₁₅Cu₂₀ GBD magnet, from 16.38 kOe to 22.38 kOe. Microstructural investigations indicated that increase in the Al content in the diffusion source can form a continuous grain boundary (GB) phase, optimizing the microstructure to enhance the coercivity. The coercivity enhancement is mainly due to the formation of a continuous GB phase to separate the main phase grains. Exchange decoupling between the adjacent main phase grains is enhanced after the GBD process. Meanwhile, the introduction of Al can effectively promote the infiltration of Pr into the magnet, which increases the diffusion rate of rare-earth elements within a certain range. This work provides a feasible method to enhance coercivity and reduce the use of rare-earth resources by partial replacement of rare-earth elements with non-rare-earth elements in the diffusion source.     

利用Pr_(70)Cu_(30)晶界扩散改善烧结钕铁硼废料矫顽力的研究

钕铁硼磁体制备过程中出现的部分块体废料由于矫顽力较低,性能难以满足使用要求.本文主要通过晶界扩散技术来提高废料磁体的矫顽力.采用Pr_(70)Cu_(30)合金作为扩散介质,对烧结钕铁硼废料磁体进行了晶界扩散处理,研究了扩散温度、扩散时间和回火时间对扩散后的磁体性能的影响.结果显示,800℃下扩散3 h,磁体的矫顽力从原来的7.88 kOe(1 Oe=79.5775 A/m)提升至11.55 kOe,提升幅度为46.6%,同时剩磁没有明显降低.扩散后回火对矫顽力的提升有一定的作用.800℃下扩散4h后的磁体在500℃回火3h后,最高矫顽力可达11.97 kOe,比原磁体废料提高了51.9%,接近成品磁体的水平.显微组织分析证实了晶界扩散的作用.扩散处理后的磁体中,主相晶粒间形成了连续晶间相,起到有效的磁隔离作用,有利于矫顽力的提高.研究还发现,Pr_(70)Cu_(30)晶界扩散虽然可以使磁体腐蚀电位上升,但也会增加腐蚀电流密度,不利于磁体抗腐蚀性的改善.本文工作对于提高材料的成品率具有重要意义.     

Effect of hot deformation temperature on the magnetic and mechanical properties of Nd-Fe-B magnets prepared by spark plasma sintering

The magnetic and mechanical properties of Nd-Fe-B magnets at different hot deformation temperatures have been investigated. The results showed that the optimum magnetic and mechanical properties and the highest crystallographic alignment of Nd-Fe-B magnets were obtained at 700 °C, and the possible reasons were analyzed. The microstructures show that abnormal grain growth is not observed at 650 °C; there exist many small spherical grains, and these small grains do not align during die upsetting. The average size of the grains and the volume fraction of coarse grains increase with increase in deformation temperature. The coarse grains do not align during die upsetting, and the non-alignment regions enlarge with increase in deformation temperature.     

取向烧结Nd-Fe-B永磁合金反磁化过程及矫顽力机理研究

本文对取向烧结Nd-Fe-B合金沿取向易轴饱和磁化后的反磁化过程分四个阶段进行了理论研究。结果表明,主相晶粒表面软磁性区成核及从表面向晶粒内部不可逆畴壁位移对Nd-Fe-B合金的矫顽力起决定性作用。矫顽力随温度升高而急速下降主要是由于热运动破坏了主相四方结构的完整性,从而使软磁性过渡区变厚所致。 关键词：     

添加Dy元素对钕铁硼速凝片微观组织和磁特性的影响

本文讨论了不同含量的Dy元素对速凝条带微观组织的影响,得出Dy的添加量为1%—2%(at%)时条带的微观结构得到最优化,柱状晶生长均匀一致,具有良好的沿c轴取向度.同时,急冷面的细小等轴晶生长区域减少,氢破后相应的磁粉抗氧化性能增强. 关键词： 速凝片 织构 微观组织 氢破     

Improvement in coercivity,thermal stability,and corrosion resistance of sintered Nd-Fe-B magnets with Dy_(80)Ga_(20) intergranular addition

To investigate the coercivity,corrosion resistance,and thermal stability of Nd-Fe-B magnets,their properties were investigated at room and high temperature before and after doping with Dy_(80)Ga_(20)(at.%) powder.The coercivity of the magnets increased from the undoped value of 12.72 kOe to a doped value of 21.44 kOe.A micro-structural analysis indicates that a well-developed core-shell structure forms in the magnets doped with Dy_(80)Ga_(20) powder.The improvement in magnetic properties is believed to be related to the refined and uniform matrix grains,continuous grain boundaries,and a hardened(Nd,Dy)_2Fe_(14)B shell surrounding the matrix grains.Additionally,the doped magnets exhibit an obvious improvement in thermal stability.For the magnets with added Dy_(80)Ga_(20) powder,the temperature coefficients of remanence(α) and coercivity(β) increased to-0.106%℃~(-1) and-0.60%℃~(-1) over the range 20-100 ℃,compared to temperature coefficients of-0.117%℃~(-1)(α) and-0.74%℃~(-1)(β) in the regular magnets without Dy_(80)Ga_(20) powder.The irreversible loss of magnetic flux(Hirr) was investigated at different temperatures.After being exposed to 150 ℃ for 2 h,the Hirr of magnets with 4 wt.%Dy_(80)Ga_(20) decreased by ~95%compared to that of the undoped magnets.The enhanced temperature coefficients and Hirr indicate improved thermal stability in the doped Nd-Fe-B magnets.The intergranular addition of Dy_(80)Ga_(20) also improved the corrosion resistance of the magnets because of the enhanced intergranular phase.In a corrosive atmosphere for 96 h,the mass loss of the sintered magnets with 4 wt.%Dy_(80)Ga_(20) was 2.68 mg/cm~2,less than 10%of that suffered by the undoped magnets(28.1 mg/cm~2).     

Elastic moduli of nanocrystalline binary Al alloys with Fe,Co, Ti,Mg and Pb alloying elements

The paper studies the elastic moduli of nanocrystalline (NC) Al and NC binary Al–X alloys (X is Fe, Co, Ti, Mg or Pb) by using molecular dynamics simulations. X atoms in the alloys are either segregated to grain boundaries (GBs) or distributed randomly as in disordered solid solution. At 0 K, the rigidity of the alloys increases with decrease in atomic radii of the alloying elements. An addition of Fe, Co or Ti to the NC Al leads to increase in the Young’s E and shear μ moduli, while an alloying with Pb decreases them. The elastic moduli of the alloys depend on a distribution of the alloying elements. The alloys with the random distribution of Fe or Ti demonstrate larger E and μ than those for the corresponding alloys with GB segregations, while the rigidity of the Al–Co alloy is higher for the case of the GB segregations. The moduli E and μ for polycrystalline aggregates of Al and Al–X alloys with randomly distributed X atoms are estimated based on the elastic constants of corresponding single-crystals according to the Voigt-Reuss-Hill approximation, which neglects the contribution of GBs to the rigidity. The results show that GBs in NC materials noticeably reduce their rigidity. Furthermore, the temperature dependence of μ for the NC Al–X alloys is analyzed. Only the Al–Co alloy with GB segregations shows the decrease in μ to the lowest extent in the temperature range of 0–600 K in comparison with the NC pure Al.     

Mössbauer effect study of γ-FeMn alloys

The disordered antiferromagnetic γ-FeMn alloys in the range of Mn concentration from 0 up to 50 at.% Mn were investigated by means of X-ray diffraction analysis (XRD), differential scanning calorimeter (DSC) and Mössbauer spectroscopy (ME) at room temperature and at 80 K. The lattice parameter is constant for Mn contents below 27 at.% and increases linearly for higher Mn concentration. The RT Mössbauer spectra for the alloys with less than 20 at.% Mn were fitted with quadrupole splitting (QS) distribution, and above 20 at.% Mn they were fitted with magnetic hyperfine field (HF) distribution. The averageQS decreases, while the HF maintain a constant value by increasing the Mn concentration. At 80 K, the HF increases linearly up to 30 at.% Mn and then maintains a constant value at about 38 kOe. The peak of the specific heat (c _p) at the Néel temperature changes from broad to sharp as the Mn content increases. The Néel temperature increases with Mn concentration.     

Superconducting transition of amorphous TiFe,ZrFe and HfFe produced by Fe implantation

Amorphous TiFe, ZrFe and HfFe alloys prepared by low temperature implantation of about 10 at% Fe were found to have superconducting transition temperatures, T_c, enhanced above the values of the pure crystalline elements. In addition, T_c = 2.6 K for TiFe is about 1 K higher than T_c of the equivalent amorphous TiCu alloy. A correlation between the recently observed dband behavior of similar binary transition metal alloys and the forming ability is extended to (Ti,Zr,Hf)-Fe alloys to explain their superconducting properties.     

Nanocrystalline soft ferromagnetic Ni-Co-P thin film on Al alloy by low temperature electroless deposition

Soft ferromagnetic ternary Ni-Co-P films were deposited onto Al 6061 alloy from low temperature Ni-Co-P electroless plating bath. The effect of deposition parameters, such as time and pH, on the plating rate of the deposit were examined. The results showed that the plating rate is a function of pH bath and the highest coating thickness can be obtained at pH value from 8 to10. The surface morphology, phase structure and the magnetic properties of the prepared films have been investigated using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and vibrating magnetometer device (VMD), respectively. The deposit obtained at optimum conditions showed compact and smooth with nodular grains structure and exhibited high magnetic moments and low coercivety. Potentiodynamic polarization corrosion tests were used to study the general corrosion behavior of Al alloys, Ni-P and Ni-Co-P coatings in 3.5% NaCl solution. It was found that Ni-Co-P coated alloy demonstrated higher corrosion resistance than Ni-P coating containing same percent of P due to the Co addition. The Ni-Co-P coating with a combination of high corrosion resistance, high hardness and excellent magnetic properties would be expected to enlarge the applications of the aluminum alloys.     

Enhancement of cube texture in Ni by the addition of W or Mo

The development of cube texture after heavy cold rolling (～95%) and annealing has been studied in pure Ni, Ni–5 at% W and Ni–5 at% Mo alloys. The two Ni alloys develop a much sharper cube texture compared to pure Ni, thus indicating the beneficial effect of W or Mo addition. W and Mo enhance the cube texture intensity in Ni by decreasing the volume fraction of the rotated cube grains. The impact of W and Mo addition is seen from a very early stage of recrystallization, where rotated cube grains form in pure Ni as opposed to sharp cube-oriented grains in the two Ni alloys. The results negate the widely perceived theory of ‘detrimental effect of impurities’ on the development of cube texture.     

ICP-AES法测定钕铁硼永磁材料中常量元素

研究了等离子发射光谱法 (ICP AES)直接测定钕铁硼永磁材料中常量元素Nd ,Fe,B的方法。选择了合适的分析线 ,采用基体匹配法消除样品中基体元素的干扰。详细讨论了ICP AES法测定硼的“记忆效应”及其消除方法。以多点 (3个点 )标准曲线法减小测定的误差。本方法已应用于钕铁硼产品的快速检验 ,样品中Nd ,Fe,B含量测定的相对标准偏差分别为 0 6 2 % ,0 5 6 % ,0 90 %     

Undersize solute element effects on defect structure development in copper under electron irradiation

We conducted systematic experiments of defect structure development in Cu base binary alloys under 1000 kV electron irradiation at temperatures higher than 300 K, using in situ observations with high voltage electron microscopy. This report describes the effects of undersize elements: Co (–3.78%), Ni (–8.45%) and Be (–26.45%). The volume size factors are given in parentheses. The amounts of the respective elements were 2, 0.3, 0.05 at.%, or less. In Cu–Ni and Cu–Co and in the reference Cu, temperature dependence of the number density of interstitial-type dislocation loops had a down peak (i.e. loops hardly formed) at approximately 373 K, attributed to unexpected impurity atoms. Above the down-peak temperature, the addition of Co or Ni increased the loop number density through continuous nucleation of loops, extended the loop formation to higher temperatures, and decreased the apparent activation energy of loop growth rate. The addition of Be for 0.3 at.% or more delayed loop formation after formation of stacking fault tetrahedra (SFTs) around 300 K. The apparent mobility of self-interstitial atoms is expected to be smaller than that of vacancies because of strong binding with Be. Loop formation at temperatures higher than 373 K was enhanced by Be for 0.3 or 2 at.%, although it was suppressed greatly for 0.05 at.% or less. All undersize atoms increased the stability of SFTs under irradiation. Mechanisms of those effects were discussed and were briefly compared with earlier results found for oversize elements in Cu.     

Effect of rare earth on the microstructures and properties of a low expansion superalloy

A new Fe-Ni-Co-Nb-Ti-Si superalloy containing trace additions of selective rare earths and having good combination of very low thermal expansion coefficient, high-resistance to stress accelerated grain boundary oxygen embrittlement and fairly good notch-bar rupture strength has been successfully developed. The resistance to oxidation for long time exposure at high-temperatures and the stress rupture life has been improved significantly with trace yttrium addition. The microstructures of the alloys have been studied by means of analytical electron microscopy, chemical and X-ray analysis techniques. The results reveal that the trace yttrium segregates in the strengthening phase with platelet morphology, and helps in transforming A(3)B type epsilon phase into A(5)B type H. The morphology and crystal structures of the grain boundary phases also change with selective additions of rare earth elements. Compared with those in the conventional alloy, the platelet precipitates in the yttrium-containing alloy densely segregate within the grains and along the grain boundaries with smaller size. The segregation of the platelet precipitates within the grains is helpful in improving the strength of the alloy. In addition, its precipitation along the grain boundaries can improve the resistance to stress accelerated grain boundary oxidation and stress rupture property of the alloy and thereby contribute to its temperature stability.     

Nd-Fe-B/FeCo多层纳米复合膜的结构和磁性

制备了Nd₂₈Fe₆₆B₆/Fe₅₀Co₅₀多层纳米复合磁性薄膜，对溅射态和650℃退火处理15 min试样的相成分分析和微结构的观察显示，溅射态薄膜呈非晶态，经650℃退火处理15 min后，薄膜主要相成分为硬磁性Nd₂Fe₁₄B相和软磁性相FeCo(110)相.Nd₂Fe₁₄B相呈柱状，其易磁化c轴垂直于膜面，尺寸约10 nm.在硬磁性相和软磁性相之间存在少量富Nd相和非晶态，富Nd相大小约7 nm.磁性测量和分析表明，1)该系列薄膜退火态具有垂直于膜面的磁晶各向异性.2)对于固定厚度(10 nm)层Nd-Fe-B和不同厚度(t_FeCo=1—100 nm)层FeCo多层纳米复合膜,剩磁随软磁相FeCo 厚度的增加快速增加，而矫顽力则减小.当t_FeCo=5 nm时，最大磁能积达到200 kJ/m³. 3)硬磁相Nd-Fe-B层和软磁相FeCo层之间交换耦合导致剩磁和磁能积增强. 关键词： Nd-Fe-B/FeCo多层纳米复合膜 交换耦合 磁各向异性     

Magnetic hyperfine properties in FeZrB‐type nanocrystalline metallic alloys

Transmission Mössbauer spectra were performed on FeZrB nanocrystalline alloys with high crystalline fraction (≈60%)at temperatures comprised within the range 77–600 K. We report the temperature dependencies of the magnetic hyperfine data of the three contributions: the crystalline bcc‐Fe grains, the residual amorphous phase, and the interface intermediate between the bulk of crystalline and amorphous phases. The evolution of the average value of the hyperfine field characteristic of the residual amorphous phase is discussed in terms of interactions between crystalline grains transmitting through the intergranular phase.     

Fe基非晶态合金的低温电阻研究

本文报道Fe_100-xB_x,Fe_87-xSi_xB₁₃,(Fe_1-xCo_x)₇₈Si_9.5B_12.5,(Fe_1-xM_x)_80-84B_16-20(M=Zr,V,Nb,Ta,Cr,Mo,W,Mn)非晶态合金的 关键词：     

纳米NiAl-Ni和Ni3Al-Ni合金的低温电阻特性

为了深入理解纳米Al-Ni合金低温下的电子输运过程，使用自主研发的电磁感应加热-自悬浮定向流法制备出Al，Ni和Al-Ni纳米合金粉末，并采用真空热压设备将纳米粉末压制成纳米晶块体，利用自主搭建的低温热电测量系统研究了Al-Ni纳米合金的电阻率随温度(8~300 K)的变化规律。研究结果表明:Al-Ni纳米合金由于形成有序晶相而仍然与Al，Ni纳米晶一样，电阻率随温度的降低而降低。纳米Ni₃Al-Ni和NiAl-Ni在居里温度点附近出现了电阻率随温度变化的极大值点，因为单质Ni的影响，Ni₃Al-Ni的居里温度比粗晶Ni₃Al提高了20 K。由于磁子-电子散射作用和声子-电子散射作用，纳米Ni₃Al-Ni，NiAl-Ni和Ni的电阻率在低温下(8~40 K)与温度呈T2和T4关系。     

Effect of Fe addition on the crystallization behaviour and Curie temperature of CoCrSiB-based amorphous alloys

The crystallization behaviour and Curie temperature of melt-spun Co_{71? x} Fe _x Cr₇Si₈B₁₄ (x?=?0, 2, 3.2, 4, 6, 8 and 12?at.%) amorphous alloys have been studied. Differential scanning calorimetry (DSC) showed two stages of crystallization. The first stage of crystallization (T _X1) in the alloy with 6?at.%?Fe was the highest and it had the highest activation energy. X-ray diffraction studies revealed that the primary crystalline phase is hcp-(CoCr)₂Si for Fe-free alloy, whereas (CoFeCr)₂Si and (CoFeCr)₃Si phases were formed with the addition of Fe. hcp-Co was also formed along with these phases. The secondary crystalline phases were fcc-Co and various boron-rich phases. The Curie temperature of the alloys also changed with the addition of Fe to the system. Like the primary crystallization temperature, the Curie temperature of the alloys did not vary systematically with the Fe content. The addition of Fe to the Co-based system changes the nearest-neighbour interaction. This changes the exchange interaction between the transition metal elements. Due to the asymmetry in the Bethe–Slater curve, a systematic variation with Fe addition was not observed in the Curie temperature measurement.