强磁场作用下材料扩散型固态相变的微观机理

为探讨强磁场对物质原子尺度行为(电子运动、离子扩散)的影响,采用光学显微镜研究强磁场作用下Fe-0.12%C合金的扩散型固态相变;采用数字多用表测量强磁场作用下的纯铝板电阻研究其电子分布.结果表明:随磁感应强度增强,Fe-0.12%C合金室温显微组织中,铁素体晶粒平行于磁场方向伸长并呈链状排列的趋势增强,珠光体团的长轴方向平行于磁场方向伸长的程度也增强;纯铝板的电阻在平行于磁场方向放置时减小,垂直于磁场方向放置时电阻有增加趋势.这是由于组成金属晶体的自由电子和排列成晶格状的金属离子在磁场作用下受到洛伦兹力的作用,随磁感应强度增强,沿磁场方向的电子浓度、金属离子扩散有增强趋势,导致磁场作用下材料扩散型相变的室温组织出现形状各向异性.     

强磁场下冷却速度对Fe-0.12%C合金显微组织的影响

研究了强磁场(12T)下冷却速度对Re-0.12%C合金中的珠光体组织形貌的影响,结果表明:强磁场下珠光体团的长轴方向与磁场方向平行且伸长的程度随其冷却速度的提高而减弱,板平面平行于磁场方向比垂直于磁场方向放置的试样的珠光体面积分数低,同时珠光体团长轴方向与磁场方向平行且伸长的程度也低,最后,探讨了强磁场下珠光体组织形貌的演变机理.     

电场作用下Cu/Cu_3Sn界面原子扩散行为的分子动力学模拟

电子产品中的钎焊点失效可能会引起整个产品报废,这种情况下电子元器件的回收利用对节约资源意义重大。实现电子元器件的连接界面分离是其有效再利用的前提。旨在为开发可行的连接界面分离技术提供理论参考,本工作运用分子动力学方法模拟研究了电场作用下电场方向和电场强度对Cu/Cu_3Sn界面原子扩散行为的影响。结果表明,电场方向对界面原子的扩散行为有显著影响,相同条件下施加正向电场的模型比未加电场的模型更容易发生扩散。进一步研究了正向不同电场强度下界面原子的扩散行为,发现电场强度的增加提高了界面附近Cu_3Sn侧原子的本征扩散系数,降低了Cu晶体侧原子的本征扩散系数,从而使得界面原子的扩散速率差异更加显著,产生的柯肯达尔效应更明显,有利于实现Cu/Cu_3Sn界面的分离。     

铝钎焊接头中Cu元素的扩散行为研究

为了研究Al-Cu共晶合金钎料中Cu元素在钎焊接头中的扩散行为,采用快速凝固技术制备了Al-Cu共晶合金钎料,以纯铝棒料为基体采用对接接头在不同温度下进行了真空钎焊,并利用SEM和EDS对接头进行了研究.研究表明:钎料中Cu原子的扩散以晶界扩散为主,当晶界上Cu原子的浓度达到一定值后开始向晶内扩散,当晶内的Cu原子饱和后又反向扩散到晶界上;钎焊温度过低、保温时间过短时,Cu元素在基体内部不能充分扩散,在基体晶界上产生严重偏析,生成Al-Cu相中最脆的θ相(Al2Cu);提高钎焊温度和保温时间有利于提高Cu元素在Al基体中的扩散,但过高的钎焊温度又导致θ相的重新出现,选取合适的钎焊工艺参数才能获得良好的钎缝.     

单向C/C复合材料基体中间相在磁场中的取向

本工作利用扫描电镜、X射线衍射仪及正交偏光显微镜研究了沥青中间相以及单向C／C复合材料基体中间相在800mT磁场中处理后的取向,证实了沥青中间相的层片平行于磁场方向;在本工艺条件下,制造的单向C／C复合材料基体中间相层片垂直于碳纤维.     

考虑层间和界面的玻璃纤维/环氧复合材料吸湿扩散实验和仿真

为研究复合材料层间和界面对吸湿扩散系数的影响,开展单向玻璃纤维/环氧复合材料和纯环氧树脂的吸湿实验,获取复合材料的三维扩散系数。采用光学显微镜和原子力显微镜分别获取复合材料层间和界面的参数。依据实验结果,建立包含层间和界面的复合材料瞬态扩散与稳态扩散有限元模型。结果表明:复合材料沿纤维方向的扩散系数大于纯树脂的扩散系数,垂直于纤维的两个方向的扩散系数不相等。包含层间的有限元模型能更真实地反映复合材料的结构及其吸湿过程,层间对垂直于纤维方向的扩散起促进作用。纬纱对沿其方向扩散的促进作用明显。为拟合复合材料的三维扩散系数,需要考虑界面扩散性能的正交各向异性。     

Cu-Fe合金的强磁场固溶时效行为

将Cu-15%Fe(质量分数)合金在强磁场中进行不同同溶时效处理,研究了合金的时效行为.结果表明,施加10 T强磁场可以促进第二相Fe枝晶的球化,而且Fe枝晶的形貌受强磁场的球化作用与高温缓慢冷却引起的粗化作用的影响.在Cu-15%Fe合金1000℃同溶处理中,施加10 T强磁场使基体中的Fe含量降低了0.39%.这表明,强磁场在一定程度上促进了Fe在Cu基体中的析出,获得与缓冷相类似的效果;施加10 T强磁场固溶处理并在10 T强磁场作用下经500℃时效处理后,基体中的Fe含量较低.其原因是,施加强磁场后Fe原子的析出规律受温度制度和析出相磁性转变的共同影响.施加强磁场改变了原子的激活能,进而影响了原子的扩散行为.     

Fe_2O_3/TiO_2扩散偶的固相反应

采用扩散偶的方法研究了Fe2O3和TiO2在1373K空气气氛不同时间下的固相反应。采用场发射扫描电镜对扩散偶表面形貌进行观察和线扫描能谱分析。根据线扫描能谱分析所得的组元扩散浓度曲线,用Den Broeder改进的Boltzmann-Matano法计算出Fe2O3/TiO2扩散偶的互扩散系数,结果发现互扩散系数与Fe3+浓度呈一定的线性关系,并随着Fe浓度的升高而增大,同时用空位扩散机理讨论了Fe2TiO5的形成。     

强磁场下Al-Si过共晶合金组织细化原理研究

为了改善Al-Si合金性能,研究了强磁场对Al-Si过共晶合金组织的影响.依据热力学和晶粒形核理论,阐述了组织变化的原因.研究表明:当Al-Si过共晶合金在600℃施加强磁场并平行于磁场方向下凝固时,共晶组织被细化,但对初生硅相影响不大;磁场强度越大,细化效果越明显;强磁场降低了固态熵和磁自由能的影响,使共晶组织临界形核半径减小,而硅由于是逆磁质对其影响不大;强磁场使液态金属平行于磁场方向流动,进一步细化了组织.     

强磁场下冷却速率对Fe-0.76%C钢先共析铁素体组织的影响

研究了在12T强磁场下冷却速率对Fe-0.76%C钢中先共析铁素体的显微组织和性能的影响,结果表明:先共析铁索体晶粒的伸长方向与磁场方向的夹角随着冷速度的提高而增大,其原因是高速冷却时原子扩散减弱.在冷却速率相同的条件下,与非磁场热处理样品相比,强磁场热处理样品的先共析铁素体面积明显增加,宏观硬度下降,因为强磁场使Fe-0.76%C钢表现出更明显的亚共析钢特征.     

添加0.05％(La+Ce)对SnXCuNi焊料与Cu基板间界面组织的影响

在Sn-4.1X-1.5Cu-Ni焊料合金中添加0.05％(质量分数,下同)(La+Ce),对焊料/Cu焊点等温时效后其界面组织的变化规律以及界面金属间化合物的形成和生长行为进行分析研究,结果表明:随着等温时效时间的延长,Sn-4.1X-1.5Cu-Ni/Cu和Sn-4.1X-1.5Cu-Ni-0.05(La+Ce)/...     

Tuning magnetic properties,thermal stability and microstructure of NdFeB magnets with diffusing Pr-Zn films

Grain boundary diffusion process(GBDP) serves as a promising approach in improving magnetic properties and thermal stability of Nd FeB permanent magnets. Herein, non-heavy rare earth Pr-Zn films deposited on the magnet surface using DC-magnetron sputtering system are reported. The thermal stability and coercivity enhancement mechanism of Pr-Zn GBDP magnets were investigated. Results show that the coercivity of Pr-Zn GBDP magnet increases from 963.96 kA m~(-1) to 1317.14 kA m~(-1) without any remanence reduction. Notably, the demagnetization curve of Pr-Zn GBDP magnet still remains a high squareness ratio. The temperature coefficient of coercivity and anti-demagnetization ability of Pr-Zn GBDP magnet under high temperatures are improved after GBDP treatment. The well-optimized rare earth-rich(RE-rich) grain boundary phases and high effective anisotropy field of(Nd,RE)2 Fe14 B magnetic hardening layers surrounding main grains are the key factors to impact the magnetic properties and thermal stability of Nd FeB permanent magnets via GBDP treatment.     

Effect of thermal cycles on interface and mechanical property of low-Ag Sn1.0Ag0.5Cu(nano-Al)/Cu solder joints

Low-Ag content SnAgCu solder has drawn more and more researchers’ attention due to the low cost. In this paper, the effect of 0.1 wt% nano-Al particles on interface reaction between Sn1.0Ag0.5Cu and Cu substrate was investigated, and the growth of intermetallic compounds (IMC) and mechanical property of solder joints during ??55 to 125 °C thermal cycling were also analyzed. The results show that the Cu₆Sn₅ IMC formed at the as-soldered interface and grow obviously with the increase of thermal cycling. The growth rate of IMC in the SnAgCu–0.1Al/Cu is lower than that of SnAgCu/Cu, which indicates that the nano-Al particles can inhibit the diffusion coefficient of IMC layers. Moreover, the shear force of two kinds of solder joints decrease during thermal cycling, but the shear force of SnAgCu–0.1Al is higher than that of SnAgCu.     

Growth of diffusion layers at liquid Al–solid Cu interface under uniform and gradient high magnetic field conditions

The effect of high magnetic fields on interfacial reactive diffusion in liquid/solid (Al/Cu) couples was experimentally investigated at a temperature of 973 K. Regardless of any magnetic field, compound layers consisting of the δ, ξ₂, η₂ and θ phases were produced at the interface. The magnetic flux density, B, exerted a non-monotonic influence on the growth of the diffusion layers. Moreover, the mean thickness of the diffusion layers (parallel to B) was found to be always greater than that of the diffusion layers (perpendicular to B) under the applied magnetic fields. These phenomena should be attributed to the effects of two types of the Lorentz force under a uniform high magnetic field on diffusion behavior. In addition, the growth of intermetallic phases could be retarded by a magnetic field gradient due to the magnetic force in the axial direction.     

High magnetic field controlled interdiffusion behavior at Bi-Bi<Subscript>0.4</Subscript>Sb<Subscript>0.6</Subscript> liquid/solid interface

The effects of a high magnetic field on the interdiffusion behavior at liquid Bi/solid Bi_0.4Sb_0.6 interface have been experimentally investigated. It was found that the migration of the interface due to interdiffusion decreased markedly with the increasing strength of magnetic field. This was relevant to the increasing of the viscosity in the liquid metal under a high magnetic field, which in turn caused diffusion activation energy to increase. As a consequence, in the presence of a high magnetic field, a considerable decrease in the effective diffusion coefficient occurred. Moreover, the retarding effect of magnetic field gradient on diffusion was found to be more significant than that of a uniform magnetic field.     

碳纳米管磁化氢等离子体薄膜的微波吸收特性

为从理论上掌握有外加静磁场存在时铁催化高压歧化生成的碳纳米管中氢等离子体的微波吸收特性,根据磁离子理论和Appleton-Hartee方程,采用W.K.B近似方法,导出了碳纳米管磁化氢等离子体薄膜的微波衰减系数公式,数值计算了不同条件下碳纳米管磁化氢等离子体薄膜在0.3～30 GHz频段的微波衰减系数。研究结果表明:随着外加磁场强度的增加,Att30.00 dB/cm的频宽明显增大,吸收峰向高频方向移动.适当控制碳纳米管中等离子体的自由电子密度、电子碰撞的有效频率和外加磁场强度,能够实现碳纳米管中磁化氢等离子体薄膜对对特定微波段的强吸收.在外磁场等于0时,运用所构建的微波吸收模型得到的数值计算结果与已有的实验数据相吻合.     

Effect of High Magnetic Field on Growth Behavior of Compound Layers during Reactive Diffusion between Solid Cu and Liquid Al

The effect of magnetic field on the growth behavior of compound layer was examined at the interface between the solid Cu and liquid Al during reactive diffusion. It was found that the thickness of compound layer was reduced by the high magnetic field. The growth activation energy in β, γ1 and ε2 layers under a high magnetic field was larger than those in non magnetic circumstances, the increment percentage being 4.8%, 13.3% and 5.5%, respectively.     

Tuning exchange spring effects in FePt/Fe(Co) magnetic bilayers

Structural and magnetic properties of exchange spring magnets consisting of hard magnetic (FePt) and soft magnetic (Fe and Co) bilayers, prepared by ion beam sputtering method are studied via X-ray diffraction (XRD), magneto-optic Kerr effect (MOKE) and vibrating sample magnetometry (VSM). Thin tracer layers of ⁵⁷Fe were introduced in the soft layer in order to observe the Fe spin structure and interfacial diffusion by Conversion Electron Mössbauer Spectroscopy (CEMS). The observed in-plane exchange spring behavior extends also to the magnetic hard layer, whose switching field can be tuned in an unexpected manner via the top soft magnetic layer. To explain the observed phenomenon it is suggested that the increased switching field, found in the system with a Co/Fe bilayer acting as a single soft magnetic layer, is compatible with a peculiar behavior of the stiffness coefficient of the heterogeneous soft magnetic layer. According to this observation, possibilities to maximize the exchange spring effects via suitably chosen non-homogeneous soft magnetic layers are open.     

电磁胀形管坯所受磁压力的瞬态分布

管坯所受磁压力的准确求解是电磁成形变形分析,优化成形系统工艺参数的基础.通过ANSYS/EMAG软件,用远场单元来说明磁场在远场区间的耗散问题,对电磁胀形时作用在管坯上的磁压力进行准确计算.在线圈长度一定的条件下,讨论了管坯尺寸对磁压力瞬态分布和磁场扩散的影响,并根据管坯端部径向磁压力和中部径向磁压力的比值,提出以磁压力分布不均匀系数来反映磁场不均匀分布的程度.计算结果表明:当管坯和线圈的相对长度大于1时,管坯上与线圈等高处承受轴向拉应力,磁场扩散现象不严重;当相对长度小于0.92时,管坯端部承受轴向压应力,磁场扩散现象严重,相对长度0.92时为电磁胀形均匀成形的条件.