烧结稀土钕铁硼磁体的物理稳定性与提升方法探讨

烧结稀土钕铁硼作为一种重要的功能材料，被广泛应用于汽车、医疗器械和航空航天等领域。本文综述了烧结稀土钕铁硼的制备与应用、物理稳定性控制，通过粉末冶金制备工艺，优化稀土钕铁硼合金成分和调控晶界结构，探索影响其稳定性的微观机理，分析烧结钕铁硼磁体在不同条件下的稳定性，指出稀土钕铁硼磁材的化学成分、微观组织结构对其磁场稳定性和温度稳定性的作用。     

细晶工艺制备高性能烧结钕铁硼的研究

研究了烧结钕铁硼制备中磁粉粒度与烧结温度以及磁性能之间的关系。研究结果表明:随着磁粉粒度的降低,磁体的矫顽力Hcj增加;但磁粉粒度降低至2.4μm以下时,Hcj不再继续增加,反而降低。另外,对比研究了采用细晶工艺制备的Co含量不同的钕铁硼磁体的耐蚀性能,结果表明Co可以显著改善磁体的失重。     

烧结钕铁硼粉末粒度对磁性能的影响

利用粉末冶金法生产烧结钕铁硼磁体，原始粉末的大小对烧结磁体的性能影响很大。原始粉末越粗，烧结温度应该越高，才能充分利用液态烧结的优势，使其性能尽可能高。本文介绍了烧结钕铁硼材料的粒度对磁性能造成的影响。研究表明，细而均匀的粉末粒度有助于样品磁性能的提高。经过改进烧结制度，可以部分地弥补由于粉末较粗而带来的不利影响。但是，当粉末粒度过于粗时，改进烧结过程也不能达到工艺要求。     

烧结钕铁硼磁体表面Zn-Co合金镀层制备工艺与耐蚀性能

采用氯化物镀液体系在钕铁硼磁体表面制备Zn-Co合金镀层,优化了Zn-Co合金镀层制备过程中的电镀工艺参数(镀液pH值、镀液温度、电流密度以及添加剂浓度),通过中性盐雾试验(NSS)、扫描电子显微镜(SEM)和动电位极化曲线,系统研究了Zn-Co合金镀层的显微组织及耐蚀性能。结果表明:烧结钕铁硼电镀Zn-Co合金镀层的最佳电镀工艺参数为:添加剂浓度为15 mL/L,pH值为4,电镀温度为25℃,电流密度为1 A/dm~2。在最佳工艺条件下制备的Zn-Co合金镀层经钝化后其耐中性盐雾时间可达120 h。合金镀层结构致密,有效填补了钕铁硼磁体的固有缺陷,为后期钝化形成致密钝化膜提供了材料基底基础。钝化后的Zn-Co合金镀层表面平整光亮,动电位极化曲线测试表明,相比Zn镀层,钝化后的Zn-Co合金镀层的自腐蚀电流密度下降了一个数量级,表明Zn-Co合金镀层钝化后具有更加优异的耐腐蚀性能。     

我国烧结钕铁硼产业的发展及其生产工艺

论述了我国烧结钕铁硼产业的发展,并总结了近年来高性能烧结钕铁硼磁体生产工艺及装备的发展,同时指出我国是钕铁硼生产大国,但不是钕铁硼生产强国,应深入研究烧结钕铁硼磁体生产工艺和设备,提高我国钕铁硼磁体的产品质量,才能增加企业自身的竞争力.     

英国开发钕铁硼磁体精密成形生产工艺

精密成形工艺的目的是按用户要求的形状生产成形后无需再机加工。最近英国伯明翰大学建立了材料精密成形实验室,研究项目之一就是开发钕铁硼永磁体的精密成形生产工艺。大多数高技术应用都要求钕铁硼永磁体具有精密的形状和尺寸。目前生产的钕铁硼磁体经过磨削加工后才能满足要求,而磨削加工的成本在钕铁硼磁体总成本中占有很大比例,采用精密成形工艺能够降低钕铁硼磁体生产成本,使其应用更为广泛。英国开发钕铁硼磁体精密成形生产工艺     

日本永磁体生产状况

包括硬磁铁氧体在内的永磁体可按其制造方法和材质加以划分,主要制品有（１）铸造磁体（用铸造法制得的铝镍钴Ａｌｎｉｃｏ磁体,铁铬钴磁体等）,（２）铁氧体磁体（粉末烧结）,（３）稀土磁体（用粉末烧结制得的钐钴磁体、钕铁硼磁体等）,（４）粘结磁体（用磁粉和粘结剂的混合物通过注射成形,压缩成形或挤压成形制得的塑料磁体、橡胶磁体等）．日本国内长期生产的铸造磁体和铁氧体磁体产量正在逐年减少,在稀土磁体之中的钕铁硼磁体有逐年增长的趋势。就世界市场状况来看,各种磁体的需求都在不断增长,随着附加价值不断提高和需求用…     

烧结NdFeB磁体热浸镀55Al-Zn合金研究

试验了烧结钕铁硼表面热浸镀 5 5Al Zn工艺 ,发现在烧结钕铁硼表面没有形成与镀覆材料之间的冶金结合 ,其原因是由于烧结钕铁硼磁体特殊的组织分布造成的 ,提出了烧结钕铁硼磁体热浸镀金属的条件。     

高频稀土永磁电机用高性能低涡流烧结钕铁硼磁钢制造技术获突破

正近日,由包头金山磁材有限公司研发的高频稀土永磁电机用高性能低涡流烧结钕铁硼磁钢制造技术获得突破。项目采用多合金技术,不同合金根据特性分别进行成分、氧含量及组织结构控制,使磁体保持低的电导率,同时有较好的富钕相分布及优良的显微组织结构;磁体后加工采用特定单元划分与组合,局部采用高温固化绝缘胶粘接处理,使磁体高频工况时发热降低。在成形工艺上,采用异形产品一次成形工艺,减少投料比,减少后加工程序及人员投入,降低生产制造成本。项目的实施,既改善了高频应用领域磁体涡流发热高的问题,同时磁体综合磁性能大于74,也是高磁能积、高矫顽力双高磁体在性能方面的一次突破。     

烧结NdFeB磁体热浸镀55A1-Zn合金研究

试验了烧结钕铁硼表面热浸镀55A1-Zn工艺，发现在烧结钕铁硼表面没有形成与镀覆材料之间的冶金结合，其原因是由于烧结钕铁硼磁体特殊的组织分布造成的，提出了烧结钕铁硼磁体热浸镀金属的条件。     

Grain resolved orientation changes and texture evolution in a thermally strained Al film on Si substrate

Temperature changes induce thermal stresses in thin films on substrates due to differences in the thermal expansion coefficients. Repeated thermal cycling may finally lead to severe surface roughening and a change in film texture. In this study we investigate the orientation changes for a 600 nm thick Al film during subsequent thermal cycles between 25 °C and 450 °C by analyzing individual grains. The results reveal orientation changes by up to 3° after one thermal cycles and unexpected large orientation gradients within individual grains.     

Dendrite growth morphologies in aluminium alloys

Different aluminium alloys, in particular Al–Cu, Al–Mg and Al–Si, have been directionally solidified under well-controlled thermal and convection conditions. For relatively high solidification rates, particular growth morphologies were observed. The most common is linked with the formation of feathery grains: these are constituted by series of twinned lamellae, in which the dendrites have 110 trunks cut through by {111} twin planes. These grains undergo a selection mechanism which is similar to that occurring for regular 100 dendritic grains. The dendritic growth along 110 crystallographic directions is supposed to be due to a change in the anisotropy of certain properties of the alloy, such as the solid/liquid interfacial energy and/or the atom attachment kinetics. When solidification conditions become less favourable to 110 growth morphologies, a mixed dendritic form containing 110 trunks and 100 arms may be obtained. In the case of the 5182 Al–Mg type alloy, 110 columnar grains which were not twinned could be observed together with feathery crystals. The possibility of such changes in the growth direction of aluminium alloys was further demonstrated by the observation of dendrites of Al–Cu–Mg solidified in a Bridgman device. In this case, 112 dendrites grow and progressively change their growth direction, thus showing curved shapes.     

Kinetics of phosphorus segregation at grain boundaries of low-alloy low-carbon steel

In a temperature range of 280–320°C, the mechanism and kinetics of segregation of impurities in steels have yet remained insufficiently studied. Under these conditions diffusion of impurities in the bulk of steel grains practically ceases, and for describing the kinetics of the process it is incorrect to use the Langmuir-McLean equation. In this work we put forward two new approaches to describe the mechanism and kinetics of phosphorus segregation in steels: a model of sequential changes in the state of phosphorus based on first-order reactions and a model of diffusion redistribution of phosphorus between boundaries of carbide precipitates, structure defects, and boundaries of steel grains. A comparative analysis of the suggested models has been conducted, and estimates of the kinetics of segregation based on them have been made; these estimates have been compared with the experimental results obtained in the temperature range of 280–320°C for test times to ～20 years. It has been shown that these models fairly well describe the experimental kinetics of phosphorus segregation in boundaries of steel grains.     

Microstructure and crystal growth direction of Al-Mg alloy

The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg alloys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basically same for the alloys prepared by these two methods. The primary grains change from cellular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cellular or columnar grain region and the primary trunk spacing decrease. All of these changes are mainly attributed to the constitutional supercooling resulting from Mg element. Comparatively, the cellular or columnar crystals of the directionally solidified alloys are straighter and more parallel than those of the permanent mould casting alloys. These have straight or wavy grain boundaries, one of the most important microstructure characteristics of feathery grains. However, the transverse microstructure and growth direction reveal that they do not belong to feathery grains. The Mg seemingly can affect the crystal growth direction, but does not result in the formation of feathery grains under the conditions employed in the study.     

AZ31镁合金压缩变形微观织构演变规律

采用电子背散射衍射(EBSD)原位跟踪实验方法研究了AZ31镁合金压缩变形微观织构演变规律。在温度为170℃条件下,研究了AZ31镁合金轧制板材经过3次连续真空压缩(变形量分别为11%、17%和23%)时,其相同观察区域的微观织构演变。研究结果表明,AZ31镁合金轧制板材的微观织构为典型的(0001)基面织构。当温度为170℃、变形量为11%时,晶粒取向发生显著改变,大部分晶粒都发生了完全孪生,只有少数发生部分孪生,原始的基面轧制织构大幅减弱,孪生变体符合60°/1010和86.3°/1210取向关系。随着变形量的增加,滑移开始启动,孪晶晶界减少,织构变化不明显。压缩变形过程微观织构演变机理主要以拉伸孪生为主,基本上没有压缩孪生出现。     

Deformation-induced austenite grain rotation and transformation in TRIP-assisted steel

Uniaxial straining experiments were performed on a rolled and annealed Si-alloyed TRIP (transformation-induced plasticity) steel sheet in order to assess the role of its microstructure on the mechanical stability of austenite grains with respect to martensitic transformation. The transformation behavior of individual metastable austenite grains was studied both at the surface and inside the bulk of the material using electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD) by deforming the samples to different strain levels up to about 20%. A comparison of the XRD and EBSD results revealed that the retained austenite grains at the surface have a stronger tendency to transform than the austenite grains in the bulk of the material. The deformation-induced changes of individual austenite grains before and after straining were monitored with EBSD. Three different types of austenite grains can be distinguished that have different transformation behaviors: austenite grains at the grain boundaries between ferrite grains, twinned austenite grains, and embedded austenite grains that are completely surrounded by a single ferrite grain. It was found that twinned austenite grains and the austenite grains present at the grain boundaries between larger ferrite grains typically transform first, i.e. are less stable, in contrast to austenite grains that are completely embedded in a larger ferrite grain. In the latter case, straining leads to rotations of the harder austenite grain within the softer ferrite matrix before the austenite transforms into martensite. The analysis suggests that austenite grain rotation behavior is also a significant factor contributing to enhancement of the ductility.     

The effect of titanium support on the morphological properties of growth of titanium-oxide nanotubes and platinum deposit

It is shown that the thickness and structure of the layer of titanium-oxide nanotubes obtained by anodization of titanium foil in fluoride-containing solutions are determined by crystallographic orientation of surface metallic grains. In addition, this orientation appears when platinum deposits are applied onto nanooxide. Optical microimages in polarized light can be used for estimation of the quality of the crystallographic orientation of surface metallic grains, as well as for control of the thickness of oxide nanotubular layers. Shiny grains are characteristic for a nonuniformly (steplike) etched support with formation of a “humpy” light-scattering grain structure. Dull grains usually have the flat (0001) orientation; the process of nanotube growth occurs uniformly over the surface and is considerably hindered, which is probably related to the higher atomic density of the (0001) plane and protective properties of the barrier oxide. It is shown that TiO₂ nanotubes are formed at a growing rate on bright grains and grains with the crystallographic orientation allowing formation of a thick oxide layer.     

电磁搅拌制备半固态材料非枝晶组织的形成机制

半固态材料具有非枝晶固相晶粒均匀分散悬浮于液态基体中的特殊结构。提出了半固态材料中非枝晶组织的形成机制 ,即“晶粒漂移和混和抑制机制”。在电磁搅拌引起的强烈混和对流作用下 ,熔体的动态凝固过程不同于常规铸造时的静态凝固过程。混和对流作用改变了熔体中的传热和传质过程 ,从而决定了凝固组织。晶粒漂移作用极大地增大了非均匀形核率 ,从而细化晶粒 ;混和抑制作用则改变了晶粒生长形态 ,使晶粒在各个方向上可以较为均匀地长大 ,具有规则圆滑的形貌 ,成为非枝晶组织。     

Wear behavior of the abrasive grains used in optical glass polishing

In this work the wear behavior of cerium oxide abrasive grains during the glass polishing was studied. Polishing tests have been done by different types of cerium oxide abrasive grains. The grains have been recovered and examined during the operation. The morphology, the granulometric distribution, the chemical composition and the agglomeration phenomenon of recovered grains have been studied.     

剪切角对挤压-剪切法制备AZ31镁合金组织和压缩性能的影响

采用挤压-剪切法(ES)在不同剪切角(150°、135°和120°)下制备了AZ31棒材。采用ES工艺制备的棒材,包括直接挤压和后续剪切两部分。随后采用光学显微镜、扫描电镜和电子背散射衍射(EBSD)等方法研究了具有双峰晶粒结构的AZ31镁合金的显微组织演变,从取向分布图中可清晰的观察到细晶粒包围狭长变形粗晶的混晶结构,且大晶粒区域的占比会随应变的增加而增大。整体来看,因为应变量和动态再结晶分数都会随着剪切角的减小而增加,导致大晶粒的占比增大,而小晶粒尺寸增加。室温压缩实验中,随着剪切角的减小,屈服强度和峰值强度逐渐增大。此外,ES挤压的基面极图也会随着剪切角度的不同发生变化。