Dy_2O_3掺杂对机械球磨Nd_2Fe_(14)B/α-Fe复合磁体矫顽力的影响

用机械球磨法制备Nd_2Fe_(14)B/α-Fe复合磁体,研究了Dy_2O_3掺杂对纳米复合磁体磁性能的影响。结果表明,掺入Dy_2O_3能显著提高复合磁体的矫顽力,且随着Dy_2O_3掺杂量的增大最大矫顽力对应的退火温度降低。X射线衍射分析结果表明,掺入Dy_2O_3使Nd_2Fe_(14)B的晶格常数减小,也即Dy部分替代Nd后生成了(Nd,Dy)_2Fe_(14)B硬磁相。因此,复合磁体矫顽力的增强主要归因于硬磁相磁晶各向异性的提高。但是,硬磁相磁晶各向异性的提高缩短了有效交换耦合长度,表现为过量掺杂Dy_2O_3使矫顽力降低。     

DyF3对三明治结构热变形NdFeB磁体温度稳定性和耐腐蚀性能的影响

为了提高热变形NdFeB磁体的热稳定性和耐腐蚀性能,设计了一种添加DyF₃的三明治结构热变形磁体。通过对磁体上下端添加不同含量DyF₃粉末,调控磁体上下端晶界相的相组成、结构及成分,提高磁体的耐腐蚀性能,另一方面Dy元素部分扩散进入主相,形成了(Nd, Dy)₂Fe₁₄B相提高磁体磁晶各向异性场,优化热变形磁体的温度稳定性。利用脉冲磁场磁强计测试三明治结构热变形磁体的磁性能,得到高达2.16 T的矫顽力。利用电化学工作站测试三明治结构热变形磁体的极化曲线,其腐蚀电流速率较基体降低一个数量极。失重实验测试168 h后,近表面添加5%(质量分数)DyF₃的三明治结构热变形磁体单位表面积失重(0.061 mg·cm^-2)远低于基体单位表面积失重(1.172 mg·cm^-2)。微观结构分析表明,富Nd相和F元素、O元素和Dy元素分别生成NdF₃和Dy₂O₃化合物。XRD分析表明...     

热变形温度对Nd_(14)Fe_(80)B_6磁体矫顽力的影响研究

使用X射线衍射、扫描电镜和磁滞回线仪等研究热变形温度、平均片状晶长度、单畴晶粒占比、平均片状晶厚度对热变形Nd_(14)Fe_(80)B_6磁体矫顽力的影响。结果表明,当Nd_(14)Fe_(80)B_6热变形温度超过其富稀土晶界相熔点150~170K后,磁体矫顽力从737kA/m降低到355kA/m。热变形Nd_(14)Fe_(80)B_6磁体统计平均片状晶长度L为320~500nm,单畴晶粒占比0.52~0.26,多畴晶粒的增加是热变形磁体矫顽力下降的原因。随着热变形温度的增加、变形时间的延长,平均片状晶厚度增长速度快于平均片状晶长度,对应热变形磁体矫顽力的下降。若降低变形温度在富稀土晶界相熔点附近有望提高磁体的矫顽力。     

变形量对热压/热变形纳米复合Nd_9Fe_（84.5）Co_1B_（5.5）永磁体晶粒尺寸和矫顽力的影响

采用热压/热变形工艺制备纳米复合Nd9Fe84.5Co1B5.5永磁体,研究了热变形过程中的变形量对磁体平均晶粒尺寸的影响以及由此带来的晶间相互作用和矫顽力的变化。结果表明变形量54%的磁体中的硬、软磁性相的平均晶粒尺寸分别为61.0和51.8nm,与其热压状态时的两相平均晶粒尺寸（52.1和54.0nm）接近;而变形量74%的磁体中的硬、软磁性相的平均晶粒尺寸则分别显著减小至19.2和22.4nm。随着两相晶粒尺寸的显著细化,磁体中的晶间相互作用由以静磁耦合作用为主转变为以晶间交换耦合作用为主,这导致其矫顽力提高了64%。     

α-Fe/Nd2Fe14B复合纳米晶的织构形成研究

采用X射线衍射分析(XRD)技术,研究了NdprFeCoB熔体快淬所制备的α-Fee/Nd2Fe14B纳米晶的织构形成过程.结果表明,Nd2Fe14B纳米晶具有较强的(001)织构,而α-Fe纳米晶具有(110)织构,这些织构垂直于薄带表面,且从自由面到激冷面逐渐减弱.从自由面到激冷面,Nd2Fe14B相在(001)晶面法线方向的尺寸和α-Fe相在(220)晶面法线方向的尺寸逐渐减小.在激冷面各晶面法线方向的尺寸相近,表明纳米晶的形状近似于等轴晶.α-Fe/Nd2Fei4B纳米晶织构的形成和生长受合金薄带在凝固过程中热流梯度的控制.     

放电等离子烧结制备高性能热变形Nd-Fe-B磁体

使用放电等离子烧结(SPS)可在短时间内将非晶Nd13.5Fe80.5B6粉末晶化,且可获得接近于全致密的各向同性磁体,其剩磁、矫顽力、最大磁能积分别为Br=0.8T,Hci＝1346kA/m,(BH)m=108kJ/m3.热变形后,随变形量的增加,硬磁相晶粒的取向度增加,Br及(BH)m大幅增加,在65%时达最大:B...     

Fe77Co2Zr9B10Cu2合金的制备及其磁性能

采用单辊快淬法制备了Fe77Co2Zr9B10Cu2合金,在530～750℃等温退火40 min,利用X射线衍射和振动样品磁强计研究了Fe77 Co2 Zr9 B10 Cu2合金的微观结构和磁性能。结果表明:淬态Fe77Co2Zr9B10Cu2合金为非晶、纳米晶双相结构。随着退火温度的升高,α-Fe晶体相从非晶、基体中析出,晶粒尺寸长大,晶化体积分数增加,矫顽力先减小后增大,比饱和磁化强度逐渐增大。实验结果表明,530℃退火后合金的矫顽力最小,在670℃时迅速增大。样品的磁性与其微观结构、晶粒尺寸、晶化体积分数等因素有关.     

纳米硬磁晶粒间的交换耦合相互作用和有效各向异性

以纳米Nd2Fe14B永磁材料为例,研究了硬磁晶粒间交换耦合相互作用对磁体有效各向异性的影响。结果表明晶粒间交换耦合相互作用随晶粒尺寸的减小而增强,材料的有效各向异性常数Keff随晶粒尺寸的减小而逐渐下降,Keff随晶粒尺寸的变化与矫顽力的变化规律相似。纳米单相永磁材料有效各向异性的减小是矫顽力降低的主要原因,交换耦合系数口aex实际上是各向异性的减小量。为保证纳米Nd2Fe14B材料具有较高的各向异性和矫顽力,晶粒尺寸应不小于30nm。     

Ga对HDDR磁粉热变形磁体磁性能和微观结构的影响

利用HDDR工艺制备出Nd32FebalBGax(x=0.0、0.2%、0.4%、0.6%、0.8%(质量分数))磁粉,并且对HDDR磁粉进行热压/热变形处理制备出全密度各向异性磁体。研究了热变形温度和Ga含量对Nd-Fe-B热变形磁体磁性能的影响,观测了不同Ga含量热变形磁体的微观结构,探讨了微量元素Ga的添加对用HDDR磁粉制备的热变形磁体微观结构和磁性能的影响机制。研究发现,Ga的添加能够明显减小热变形磁体的主相晶粒尺寸,改善磁体的微观织构,并可以同时提高热变形磁体的剩磁和矫顽力。当Ga含量为0.6%(质量分数)时,热变形磁体的磁能积达到最大值228.3kJ/m3。     

过冷钕铁硼合金的凝固行为

作为一种高性能的永久磁体,钕铁硼(Nd-Fe-B)合金磁体日益引起人们的很大关注,其应用领域也愈加广泛.它们的生产方法有熔体离心铸造和烧结工艺2种.人们认为,这类磁体的优越性来源于磁性的Nd2Fe14B相,它不仅具有很大的饱和磁化强度,而且具有很高的各向异性磁场.     

Crystallization Behavior of Zr_(55)Al_(10)Cu_(30)Ni_5 Bulk Metallic Glass Rolled at Room Temperature

Zr 55 Al 10 Cu 30 Ni 5 bulk metallic glass was rolled up to 95% in thickness reduction at room temperature, and the dependences of microstructure and thermal stability on the strain were investigated. It is revealed that phase transformations do not occur during the rolling, but the split of the crystallization peaks becomes more and more obvious with increasing thickness reduction. Analyses of the radial distribution functions and the pair correlation functions indicate that the rolling has enhanced the sh...     

机械合金化能量转换与Ni_(50)Ti_(50)非晶合金的形成

本文报道了球磨转速,装球量对 Ni_(50)Ti_(50)单质混合粉机械合金化的影响,并建立模型用于计算工艺条件对球磨能量转换的影响,进而讨论了它与机械合金化相变反应方式的关系。粉末在每次碰撞的变形能过高时,可能形成金属间化合物,而粉末经长时间球磨获得的总能量超过一定值将引起非晶的晶化。     

Superplasticity in Aluminium Brass(HAl 66-6-3-2)

1.IntroductionSuperplasticity is not merely a specialphenomenon for certain specific alley,but isone of the intrinsic properties of metallicmaterials[1].When the internal and externalconditions are suitable,superplasticity ofmetal materials will be presented.     

铍青铜(QBe2)超塑性与动态再结晶

本文研究了硬化态铍青铜(QBe~2)的超塑性与动态再结晶。试验表明,合金在550℃和ε=1.75×10~(-4)s~(-1)条件下拉伸变形,获得最高延伸率780％,流动应力为0.075kg/mm~2。合金通过动态再结晶(ε≈0.3)形成等轴晶粒(等轴比1.12～1.22)。高速变形时晶粒尺寸会超细化,这可能是发生连续动态再结晶所致,但延伸率不高。第二相粒子会促进动态再结晶形核和通过钉扎晶界来保持细晶粒组织。     

Cover Picture: An Investigation of the Inelastic Deformation of Cortical Bone (Adv. Eng. Mater. 8/2005)

The cover picture shows shear bands that develop during compression of cortical bone. It shows that the bands extend across the bone lamellae and are mirror symmetric with respect to the loading axis. More on the inelastic deformation of cortical bone can be found in the paper By C. Mercer and A. G. Evans on page 719..     

Organic metal (EDO-TTF)2PF6 with multi-instability

Abstract

The multi-instability of the electronic structure of (EDO-TTF)₂PF₆, where EDO-TTF means ethylene-dioxytetrathiafulvalene, is reviewed. This complex showed the metal–insulator transition at 280 K associated with distinct molecular deformations. The mechanism is interpreted as the cooperation of Peierls transition, charge ordering, and the order–disorder transition of the countercomponent. The charge ordering pattern in the low-temperature phase is of the novel [0, 0, 1, 1] type. The sensitivity of the electronic state to external perturbations is demonstrated applying not only static but also instantaneous stimuli. In the latter case, the photo-induced phase transition is ultrafast and highly efficient. One photon causes the transition of several hundreds of donor molecules in the low-temperature phase to relax into a highly conducting metastable state within about 1.5 ps. In the early stage of the transient state, the charge ordering of the [1, 0, 1, 0] type occurs. As for the chemical modifications of this material, the partial deuteration of this complex increases the metal–insulator transition temperature. The introduction of a methyl group greatly modulates the electronic structure of the complex, i.e. (methyl-EDO-TTF)₂X (X=BF₄, ClO₄) shows a two-dimensional electronic structure. The working hypotheses for developing the systems with multi-instability are described.     

Dynamic recovery: sufficient mechanism in the hot deformation of Al (<99.99)

A recent OIM study of the substructure in hot compressed Al has observed an increase in the fraction of boundaries both of 15–20° and above 20° as strain rises from 0.9 to 1.5. This was interpreted as evidence of continuous dynamic recrystallization being the mechanism for the steady state deformation. However, when the original grain boundaries and transition boundaries between deformation bands are discounted, the fraction of 15–20° boundaries is reduced to less than 20% and would be much lower if subboundaries less than 0.5° visible in TEM were taken into account. The present authors argue that dynamic recovery maintains the subgrains of constant size, low misorientation and equiaxed to produce a steady state and can permit a limited number of discrete segments with higher misorientation notably as temperature falls. Moreover, continuous dynamic recrystallization is not appropriate terminology because it is far from reaching the completion observed in other instances of continuous recrystallization.     

Novel severe plastic deformation technique—accumulated extrusion (AccumEx)

Accumulated extrusion, a novel severe plastic deformation technique based on conventional extrusion process, is proposed and has been validated on commercial pure aluminium sheets. Four sheets were extruded together at 75% reduction, and this product was recut into four pieces and reextruded up to eight passes to a strain of 13.2. The tensile strength increased up to 200?MPa after six passes. The elongation to failure was 21% after one pass and 6% after six passes. Ultrafine grains with average grain size of 600?nm were observed after eight passes. The refinement process was monitored along all three directions. Texture evolution played an influential role on the misorientation profile and high angle grain boundary fraction.     

Organic metal (EDO-TTF)2PF6 with multi-instability

The multi-instability of the electronic structure of (EDO-TTF)₂PF₆, where EDO-TTF means ethylene-dioxytetrathiafulvalene, is reviewed. This complex showed the metal–insulator transition at 280 K associated with distinct molecular deformations. The mechanism is interpreted as the cooperation of Peierls transition, charge ordering, and the order–disorder transition of the countercomponent. The charge ordering pattern in the low-temperature phase is of the novel [0, 0, 1, 1] type. The sensitivity of the electronic state to external perturbations is demonstrated applying not only static but also instantaneous stimuli. In the latter case, the photo-induced phase transition is ultrafast and highly efficient. One photon causes the transition of several hundreds of donor molecules in the low-temperature phase to relax into a highly conducting metastable state within about 1.5 ps. In the early stage of the transient state, the charge ordering of the [1, 0, 1, 0] type occurs. As for the chemical modifications of this material, the partial deuteration of this complex increases the metal–insulator transition temperature. The introduction of a methyl group greatly modulates the electronic structure of the complex, i.e. (methyl-EDO-TTF)₂X (X=BF₄, ClO₄) shows a two-dimensional electronic structure. The working hypotheses for developing the systems with multi-instability are described.