Behavior of residual carbon in Sm(Co, Fe, Cu, Zr)z permanent magnets

When sintered Sm(Co, Fe, Cu, Zr)_z permanent magnets are prepared by metal injection molding, some organic binders are added in alloy powder, which leads to much residual carbon in the magnets. The residual carbon decreases magnetic properties and destroys the microstructure of the magnets. In this paper, the behavior of carbon in Sm(Co, Fe, Cu, Zr)_z permanent magnets has been studied. The results indicate that Sm(Co, Fe, Cu, Zr)_z magnets can keep excellent magnetic properties when the carbon content is below 0.1 wt.%: Br ≥ 10 kGs, H_cj ≥ 22 kOe, BH_max ≥ 25 MGOe. When the carbon content is above 0.1 wt.%, Br, H_cj and BH_max decrease with increasing carbon content evidently. Carbon consumes Zr content and forms ZrC, which reduces the volume fraction of the lamella and Sm(Co, Cu)₅ phases. Thus, the cell size increases and the cellular microstructure deteriorates. When the carbon content reaches 0.43 wt.%, there is not enough Sm(Co, Cu)₅ phase to form a uniform cellular microstructure. Br, H_cj and BH_max are approximate to zero. Since carbon has little influence on the content of Sm₂(Co, Fe)₁₇ phase, Ms can keep a high value (≥100 emu/g). ZrC has high melting point (3420 °C) and acts as dispersion particle in the magnets, which prevents the grains of SEM structure growing and reduces the liquid content of green compacts during sintering. Therefore, the density of the magnets decreases.     

Structure and magnetic properties ofhigh-performanced Sm2（Co, Fe, Cu, Zr）17 alloys

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｈｉｇｈＣｕｒｉｅｔｅｍｐｅｒａｔｕｒｅａｎｄｌｏｗｅｓｔｔｅｍｐｅｒａ ｔｕｒｅｃｏｅｆｆｉｃｉｅｎｔｏｆｔｈｅＳｍ2 Ｃｏ17ｐｅｒｍａｎｅｎｔｍａｇｎｅｔｓｍａｋｅｔｈｅｍｂｅｉｄｅａｌｃａｎｄｉｄａｔｅｓｆｏｒｈｉｇｈｔ     

Microstructure and Corrosion Behavior of Electrodeposited Ni-Co-ZrC Coatings

In this present work, ZrC particles incorporated Ni-Co composite coatings were electrodeposited. The objective of this article is to study the influence of Co content on the microstructure and properties of Ni-Co-ZrC coatings. Pure Ni and Ni-ZrC coatings have also been electrodeposited for comparison. Surface morphology, chemical composition, microstructure, and microhardness of Ni-Co-ZrC coatings were characterized by scanning electron microscopy, energy dispersive spectrometer, x-ray diffractometer, and Vicker microhardness tester. The potentiodynamic polarization technique was applied to measure the corrosion behavior of the coatings. By increasing Co concentration in electrolyte, Co content of the coatings was modified from 0 to 80 wt.% and ZrC particles content of the coatings was reduced. As the Co content increased, the dominant phase structure was changed from face centered cubic to hexagonal close packed crystal structure. Surface morphology of the Ni-Co-ZrC coatings was changed from nodular to sharp corner structure, and finally branched morphology with increasing Co content of the coating. Among the electrodeposited coatings, Ni-Co-ZrC coating with 42 wt.% Co content exhibited the highest microhardness. The corrosion potential of the coating was shifted to more positive with increasing the Co content from 0 to 64 wt.%. The lowest corrosion rate of 4.507 × 10^?7 g·h^?1·cm^?2 was found for Ni-Co-ZrC coating at the Co content of 75 wt.%.     

In-situ observation of magnetization reversal process of Sm(Co,Cu,Fe,Zr)_z magnets with different Fe contents

Sm(Co,Cu,Fe,Zr)_z magnets have drawn much attention for high-temperature applications due to their high Curie temperature,strong corrosion resistance and thermal stability.The effect of increasing Fe content on the distribution of elements and squareness(S_r) of demagnetization curves were investigated for two kinds of magnets with different nominal compositions of Sm(Co_(bal)Fe_(0.15)-Cu_(0.07)Zr_(0.03))_(7.8) and Sm(Co_(bal)Fe_(0.28)Cu_(0.07)Zr_(0.03))_(6.6) in this work.The magnetic properties of the magnets with higher Fe content fluctuate greatly after different solution treatments,indicating that they are more sensitive to the process temperature.The increase in Fe content can obviously enhance the cellular phase size.Meanwhile,inhomogeneous Cu distribution is observed in the Sm(Co_(bal)Fe_(0.28)-Cu_(0.07)Zr_(0.03))_(6.6) magnet,resulting in the different cellular structures and corresponding magnetic domain patterns in different regions in the inner grains.Furthermore,the lower Cu content regions are responsible for the wider magnetic domain,which have weaker resistance to applied magnetic field.As a result,S_r of demagnetization curve decreases with the increase in Fe content due to the inhomogeneous Cu distribution,which was confirmed by in-situ observation of electron probe micro-analyzer(EPMA) and magneto-optical Kerr optical microscope(MOKE).     

合金元素对PrFeB永磁合金结构和磁性能的影响

简述了Co、Nb、Zr、Ga、Cu、Si等合金元素的加入对PrFeB永磁合金的结构和磁性能的影响。以上合金元素的加入，均能不同程度地提高PrFeB的磁性能，但含量超过一定比例后，永磁合金磁性能则有所下降。Co、Cu、Si的加入还有助于PrFeB合金居里温度的提高。     

SC工艺制备Sm2Co17型永磁材料的金相组织与磁性能

采用SC工艺和通用的熔炼工艺制备了Sm2Co17型永磁材料。对两种工艺所制备的合金金相组织、永磁材料的磁性能进行了研究。另外,也研究了合金时效处理对永磁材料磁性能和取向度的影响。结果表明,SC工艺制备的合金获得了希望的柱状晶结构,但其制备的永磁材料磁性能却明显偏低,取向度只有通用熔炼工艺的74%;时效处理能明显提高SC工艺制备的永磁材料的磁性能,且其磁性能与通用熔炼工艺制备的永磁材料相当。     

Effect of carbon on the coefficient of thermal expansion of as-cast Fe−30wt.%Ni−12.5wt.%Co−×C invar alloys

The segregation (distribution) of nickel and the composition of its constituents influence the low thermal expansion characteristics (Invar effect) in Fe?30 wt.% Ni?12.5wt.% Co?×C Invar alloy. The change of coefficient of the thermal expansion and magnetic properties were studied as an aspect of carbon addition causing the segregation of Ni in primary austenite of as-cast Fe?30wt.% Ni?12.5wt.% Co Invar alloy. The coefficient of thermal expansion of Fe?30 wt.% Ni?12.5 wt.% Co?×C Invar alloy showed its lowest value at 0.08 wt.% carbon, increased with increasing carbon content in the range of 0.08–1.0 wt.%C, kept constant at 1.0–2.0 wt.%C and decreased at carbon higher than 2.0 wt.%. The effective distribution of the coefficient of nickel in as-cast Fe?30 wt.% Ni?12.5 wt.% Co?×C Invar alloy increased with increasing carbon content. The volume fraction of the γ phase of Fe?30 wt.% Ni?12.5 wt.% Co?×C alloy increased with increasing carbon content. The microstructure of Fe?30 wt.% Ni?12.5 wt.% Co?×C alloy changed with the carbon content was independent of the coefficient of thermal expansion. The Curie temperature changed linearly with the carbon content and was similar to the change of the coefficient of thermal expansion. Moreover, the coefficient of thermal expansion decreased when the ratio of saturation magnetization to Curie temperature (σ_s/T_c) increased, decreasing the Curie temperature and showed a specific relationship with the magnetic properties of the Fe?30 wt.% Ni?12.5 wt.% Co?×C Invar alloy.     

金属间化合物结构材料反位缺陷及其对性能的影响

反位缺陷是金属间化合物中的本征点缺陷,它对材料的力学性能、物理性能、化学性能都有重要的影响,在某些情况下成为决定性能的关键结构要素。首先评述了反位缺陷研究理论,基于量子力学的第一性原理方法、EAM法研究结构材料反位缺陷侧重缺陷的物理和化学原理,基于Ginzburg-Landau方程的微观相场法侧重缺陷微结构演化的动态过程。然后,作者通过图解反位缺陷与传输机制之间的关系说明反位缺陷对高温结构材料的积极贡献以及对性能的危害。最后,作者通过评述常见的L12结构和B2结构反位缺陷及第三组元择优占位的研究进展,归纳了结构材料反位缺陷研究存在的问题。     

New Fe−Co−Ni−Cu−Al−Ti Alloy for Single-Crystal Permanent Magnets

A new alloy intended for single-crystal permanent magnets has been suggested. The new alloy has been designed based on the well-known Fe?Co?Ni?Cu?Al?Ti system and contains to 1 wt % Hf. The alloy demonstrates an enhanced potential ability for single-crystal forming in the course of unidirectional solidification of ingot. Single-crystal permanent magnets manufactured from this alloy are characterized by a high level of magnetic properties. When designing the new alloy, computer simulation of the phase composition and calculations of solidification parameters of complex metallic systems have been performed using the Thermo-Calc software and calculation and experimental procedures based on quantitative metallographic analysis of quenched structures. After the corresponding heat treatment, the content of high-magnetic phase in the alloy is 10% higher than that in available analogous alloys.     

30 MGs.Oe Sm-Co PERMANENT MAGNETS PREPARED BY LIQUID PHASE SINTERING

实验表明,Sm(Co,Cu,Fe,Zr)_Z 2-17磁体的最佳成份区与Ojima所报道的不同,Sm含量不是25.5％而是27.0—27.5wt％。而且简单的固相烧结难以获得优异性能。采用液相烧结工艺,有利于准确调整和控制成分,有效地发挥多级时效处理的有利作用,显著地增强矫顽力和能积,可稳定地进行大批量制备高性能磁体。最高性能可达30.5 MGs·Oe。     

Influence of zirconium addition on the microstructure and magnetic properties of nanocomposite Nd10.1Fe78.2-xCo5ZrxB6.7 permanent magnets

Nanocomposite Nd10.1Fe78.2-xCo5ZrxB6.7 （x= 0, 1.5, 2.5, 2.7, 3, 4） permanent magnets were prepared by melt-spun and annealing. The microstructure and magnetic properties of the permanent magnets were investigated. The resuits reveal that the addition of Zr element significantly reduces the grain size and improves the thermal stability of the amorphous phase. A fme nanocomposite microstructure with an average grain size of about 35 nm can be developed at a wheel speed of 16 m·s^-1 with the content of Zr up to 2.7 at.%. After optimal annealing （710℃ x 4 min）, the magnetic properties of the Ndl0.1Fe75.5Co5Zr2.TB6.7 bonded magnets were achieved as follows： Br= 0.72 T, jHc = 769 kA·m^-1, and （BH）max = 85.0 kJ·m^-3.     

成分对高温永磁体Sm(CoFeCuZr)_z显微组织和磁性能的影响

成分是影响Sm(CoFeCuZr) z 性能的关键因素之一。本文概述了成分对高温永磁体Sm(CoFeCuZr) z 显微组织和磁性能影响的研究状况。并指出了掌握成分与显微组织和磁性能的关系 ,对制造高性能高温永磁体Sm(CoFeCuZr) z 的现实意义。     

Effects of Ti and(or) Cu on microstructures and magnetic properties of sintered Nd-Fe-B magnets

1　ＩＮＴＲＯＤＵＣＴＩＯＮＩｔｉｓｗｅｌｌｋｎｏｗｎｔｈａｔｔｈｅｉｎｔｅｒｇｒａｎｕｌａｒｍｉ ｃｒｏｓｔｒｕｃｔｕｒｅｏｆｓｉｎｔｅｒｅｄＮｄ Ｆｅ Ｂｍａｇｎｅｔｓｐｌａｙｓａｋｅｙｒｏｌｅｉｎｄｅｖｅｌｏｐｉｎｇｔｈｅｉｒｃｏｅｒｃｉｖｉｔｙ[1,2 ] .Ｅａｒｌｉｅｒｓｔｕｄｉｅｓｓｈｏｗｅｄｔｈａｔｔｈｅｉｎｔｅｒｇｒａｎｕｌａｒｍｉｃｒｏｓｔｒｕｃｔｕｒｅｉｓｃｏｍ ｐｏｓｅｄｏｆａＮｄ ｒｉｃｈｐｈａｓｅａｎｄａｓｍａｌｌａｍｏｕｎｔｏｆＢ ｒｉｃｈｐｈａｓｅ.Ｉｔｈａｓｂｅｅｎｓｈｏｗｎｔ…     

ZrC增强激光熔覆CoCrNi合金熔覆层的组织及性能

本研究采用激光熔覆技术,在低碳钢表面制备了ZrC增强的CoCrNi合金涂层。研究了ZrC的不同分数(0, 1, 3, 5 wt.%)对CoCrNi基中熵合金涂层组织、硬度和耐磨性的影响。利用X射线衍射仪、扫描电镜和能谱仪分析了涂层的相组成及微观组织结构,并采用显微硬度和摩擦磨损试验对样品的硬度和耐磨性进行了测试。结果表明：熔覆层与基体形成了良好的冶金结合,没有出现明显的裂纹和及空洞等缺陷。不含ZrC的CoCrNi中熵合金涂层由单相FCC结构组成,随着涂层中ZrC的加入,涂层中的物相组成变为了FCC+ ZrC_0.7+Cr₂₃C₆+ZrO₂。涂层的晶粒得到了明显细化,实现了晶界强化、固溶强化和弥散强化(Orowan)的共同作用,形成的碳化物Cr₂₃C₆相与FCC固溶体结合形成共晶碳化物,起到了协同强化作用,有效地提高了涂层的硬度和耐磨性。然而ZrC中的Zr与空气中的杂质O结合生成的ZrO₂也对涂层的性能产生了不利影响,主要是因为ZrO₂的存在会导致涂层中颗粒分布不均匀加剧,弱化弥散强化的作用。所以当ZrC较少时,涂层的性能并未得到较好的提升,但是当涂层中ZrC含量增加到5wt.%时,涂层中析出了较多的强化相ZrC0.7能够有效的提高材料的性能,该涂层的最大硬度为651±15 HV_0.1,摩擦系数为0.161,相较于不含ZrC的涂层均有较大的提升。     

Effect of Fe on Microstructure and Coercivity of SmCo-Based MagnetsEI北大核心CSCD

High-temperature permanent magnets have an important application in the aerospace and other high-tech fields, among which 2:17-type SmCo magnets have become the first choice for high-temperature permanent magnets due to the strong magnetic anisotropy and high Curie temperature. Although there are studies on the effect of Fe on the remanence and coercivity, the role that Fe plays on coercivity mechanism of SmCo magnets is still unclear. In this work, Sm(CobalFexCu0.08-0.10Zr0.03-0.033) z (x= 0.10-0.16, z=6.90 and 7.40) magnets are prepared and the magnetic properties under different temperatures are investigated. The magnets with an intrinsic coercivity of 603.99 kA/m and a maximum energy product of 87.30 kJ/m(3) at 500 degrees C. are obtained. It is revealed that at room temperature the coercivity of the magnets increases with increasing Fe content, however, at 500 degrees C. the coercivity shows an opposite dependency on Fe content. Moreover, the effect of Fe on coercivity is more obvious at low z value. The phase structure and composition analyses were characterized by XRD and TEM. The results show that with the increase of Fe content, the size of the 2: 17R cell phase increases, the volume ratio of cell boundary 1: 5H phase decreases, and furthermore, both Fe content in the 2: 17R phase and Cu content in the 1: 5H phase increase. The variations of Fe and Cu contents in both phases lead to the change of the domain wall energy difference. With the increase of Cu content of 1:5H phase, the domain wall energy of 1: 5H phase (gamma(1:6)) drops faster at room temperature, the coercivity is determined by gamma(2:17)-gamma(1:5), so the coercivity increases with increasing Fe content. While at 500 degrees C, due to gamma(1:6) at its Curie temperature, the coercivity is mainly determined by the domain wall energy of 2: 17R phase (gamma(1:17)), which decreases with increasing Fe content. The increase of Fe content at the low z value results in a smaller growth of cell size, which leads to a more significant change in coercivity.     

Effects of graphite on the microstructure and properties of ultrafine WC-11Co composites by spark plasma sintering

Ultrafine WC-11Co hard metals added with different proportions of graphite were prepared by spark plasma sintering at 40 MPa/1200°C for 5 min,and the influence of graphite as free carbon on the microstructure and mechanical properties were investigated.The XRD analysis showed that decarbonization could be prevented by adding graphite.Compact hard metals composed of finer and more homogeneous WC grains with little flaws can be achieved after 0 wt.% to 1.5 wt.% graphite was added.The hardness and fracture toughness increase initially with increasing graphite content,and with over 1.5 wt.% they descend due to coarse grains and more defects.Therefore,1.5 wt.% graphite is the optimal addition content in view of the hardness and transverse rupture toughness.Furthermore,the coercive force decreases while the saturated magnetic intensity increases with the increase of graphite content.     

ZrC含量对TiC基金属陶瓷组织和性能的影响

真空烧结制备了TiC-ZrC-Co-Ni系金属陶瓷,研究了ZrC对TiC基金属陶瓷显微组织和室温力学性能的影响。结果表明:未加ZrC的TiC基金属陶瓷的显微组织表现为经典的黑芯-灰壳组织,硬质相形状多为球形;而加入ZrC后的金属陶瓷随着ZrC加入量的增多,组织逐渐细化,硬质相形状大多数为方形,硬质相与粘结相界面呈现直线,在黑芯周围出现白色球状(Ti,Zr)C固溶体。由于Co、Ni对ZrC的润湿性不理想,金属陶瓷的致密度随着ZrC含量的增加而下降,室温力学性能(抗弯强度、硬度、断裂韧性)也随之降低。     

z值影响Sm(CoFeCuZr)z磁性能的机理研究

通过粉末冶金法制备了不同z值(z=7.5～8.5)的Sm(CoFeCuZr)_z磁体。利用磁性能测量系统、X射线衍射分析、电子探针以及透射显微镜等对磁体的性能、组成相、析出相含量、微观结构及元素分布进行表征,通过分析解释了磁性能随z值变化的内在机理。结果表明:随z值增大,胞状结构尺寸增大,高饱和磁化强度的2:17R相增多导致剩磁Br升高;z值增大导致富Zr析出相增多,引起方形度H_k/H_(cj)下降;z值通过改变Cu元素在2:17R相界面位置的富集程度来改变矫顽力H_(cj)的大小,在一定范围内(z8.2)该位置Cu含量越高,矫顽力越大。     

Effect of sintering temperature on the structure and magnetic properties of SmCo5/Fe nanocomposite magnets prepared by spark plasma sintering

Highly dense SmCo₅/Fe nanocomposite bulk magnets were prepared by spark plasma sintering of magnetic field-milled SmCo₅/Fe nanocrsytalline powders. The sintering experiments were conducted with varying temperatures of 973–1123 K. The resultant bulk materials had densities of 85–98% and mean grain sizes of 17–30 nm. The SEM analysis showed that the bulk samples prepared at higher sintering temperature exhibited dense and uniform microstructure. The XRD studies in complement with energy dispersive X-ray analysis revealed that the bulk magnets sintered at or above 1073 K exhibited Sm(Co,Fe)₅ as main phase, along with other secondary phases such as Sm₂(Co,Fe)₁₇ and α-Fe(Co). A single-phase behavior with high remanence ratios (0.67–0.77) for the nanocomposite magnets was demonstrated by the magnetic measurements. In the present study, the sintering temperature of 1073 K was found to be optimum in achieving relatively high coercivity (8.2 kOe), magnetization (97.5 emu/g) and energy product (278.7 kJ/m³) for the SmCo₅/Fe nanocomposite bulk magnets.     

烧结(Nd,Tb)-Fe-B磁体的元素扩散、反磁化和矫顽力

采用双合金法将两种粉末混合制备烧结永磁体可提高磁体磁性能;但在烧结过程中两种粉末之间存在元素扩散,元素扩散对磁性能的影响程度需要进一步研究。本文将Nd13Fe81B6和TbHx粉末混合制备烧结磁体,Nd13Fe81B6磁体矫顽力为4.5 kOe。当TbHx混合量为3 wt.%,烧结磁体的矫顽力增加至20.0 kOe。通过热激活研究认为,磁畴壁的形核是反磁化需要经过的过程。由于热力学的原因Tb元素更容易扩散进入Nd2Fe14B主相而不是富集在晶间富稀土相。Tb元素进入主相替代Nd可形成具有更高各向异性场的(Nd,Tb)-Fe-B表层,在反磁化过程中晶粒表层磁畴壁的形核场会增加,因此矫顽力增加程度显著。但是,TbHx混合量超过5 wt.%,矫顽力增加幅度降低。对于TbHx混合量7 wt.%的磁体,元素分布显示在主相晶粒内部贫Tb区域明显增少,证实在烧结过程中更多Tb原子从晶粒表层扩散入晶粒内部,这样晶粒表层反磁化形核场的提高程度会减弱,因而磁体矫顽力增加幅度降低。本研究说明要提高双合金Nd-Fe-B磁体磁性能需进一步控制元素扩散并优化磁体的元素分布。