Fe—Mn—Cr合金晶间腐蚀电子理论研究

为了从电子层面揭示Fe—Mn—Cr合金晶间腐蚀的物理本质,采用递归法计算了合金的原子埋置能、格位能、亲和能等电子结构参数,探索合金晶间腐蚀机理。研究表明：Cr在晶内稳定性很低,Cr在晶界和表面稳定性较高,基体中的Cr首先扩散到晶界,并通过晶界扩散至合金的表面。Cr元素减小费米能级差,抑制合金的晶间腐蚀。O-Cr间的亲和能为负数,表明氧与Cr之间有相互作用,生成Cr的氧化物。当氧化膜达到一定厚度可起到保护合金的作用。碳与Cr的亲和能也为负数,且其数值比氧与Cr间的亲和能更负。合金中碳优先与Cr形成化合物,在晶界析出,造成晶界贫Cr,使合金晶间腐蚀加重。     

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.     

铬在晶界的选择性氧化

利用扫描俄歇微探针研究了氧化过程中Ni—Cr合金的表面氧化行为。经过600℃、20min的氧化后,作为选择性氧化的结果,Cr和Ni分别在晶界和晶面上以它们的氧化物形式产生富集。较小的氧化铬生成热使铬在晶界区的氧化竞争中得以占先;而晶界为铬的向表面扩散提供了通道;氧化铬的生成,使可扩散铬原子浓度梯度增加,它有利于这种扩散过程的加快。本研究为Ni—Cr合金表面形成抗氧化防腐蚀的氧化铬层提供了理论依据。     

影响Cu-Sn合金电阻率的因素

利用量子力学理论分析了成分变化对Cu-Sn合金电阻率影响的微观机理;探讨了铸态、正火态、轧制态和回火态存在的一些影响因素,如固溶体中的溶质含量、晶界、晶体缺陷和应力等对Cu-Sn合金电阻率影响的宏观机理。实验结果表明:正火处理会增加Sn原子在Cu晶粒内部的固溶量,使合金的电阻率上升;大变形量轧制后,Cu晶粒被挤压变长,晶界厚度减小,铸造缺陷基本消失,自由电子被散射的几率减小,Cu-Sn合金的电阻率会大幅度下降;回火处理可消除微观组织中的部分应力,使晶格畸变减轻和位错密度降低,可获得更低的电阻率。     

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。     

30CrMnSiA钢超塑性变形中的机理问题

利用扫描电镜和透射电镜研究了30CrMnSiA钢超塑性变形中组织结构变化。结果表明,变形中合金元素的扩散导致横向晶界的宽化,并且富集了Si、Cr、Mn元素。三角晶界上呈现的显微空洞宏观调节了晶粒的三维重排过程。未溶碳化物与晶格位错、晶界以及晶界位错之间有相互作用关系。扩散和位错运动微观调节了晶界滑动,并导致它的发展。     

镍基高温合金微孪晶形成机制的研究进展

镍基高温合金具有优良的成分兼容性、良好的组织稳定性、抗氧化和抗腐蚀性能,被广泛用于航空发动机和地面燃气轮机的涡轮叶片等关键的热端部件。沉淀相γ'对位错运动的阻碍是镍基高温合金的主要强化作用之一。一般而言,这种阻碍作用不仅与γ'相的形貌、体积分数及尺寸有关,也取决于γ'相与位错的交互作用。通常这种交互作用机制可分为三种:切割机制、Orowan绕过机制和热激活攀移机制。当不同类型的位错切割γ'相时,在γ'相中会形成不同的高能缺陷,能够阻碍位错运动,延缓材料软化。这类结构或成分缺陷包括:反相畴界(APB)、复杂层错(CSF)、超点阵内禀层错(SISF)、超点阵外禀层错(SESF)和微孪晶。微孪晶化(Micro-twinning)是镍基高温合金中一种重要的变形机制,主要发生在中温高应力条件下。此外,中温拉伸变形过程中也有微孪晶产生。早期研究表明,微孪晶的产生与SESF有关,可以认为SESF是"胚体孪晶",且SESF是由a/3〈112〉超点阵不全位错切入γ'相产生的。基于溶质原子短程扩散的原子重排(Reordering)机制被用来解释微孪晶的形成,即a/6〈112〉不全位错切入γ'相中先产生CSF,而后CSF通过原子重排转变为SESF,最终形成微孪晶。最近的研究表明,在微孪晶产生过程中,Co和Cr原子会在成分偏析和柯氏气团的作用下发生长程扩散,因此有学者指出微孪晶的形成是原子重排短程扩散机制和偏析主导的长程扩散共同作用的结果。同时,对于高温合金微孪晶机制的研究,研究人员不再局限于其形成机制,而对微孪晶的长大机制有了进一步的理解。共格的纳米孪晶界作为金属材料中的一种特殊缺陷,可以有效阻碍位错运动,从而强化材料,这种强化方式已经在纳米铜、TWIP钢以及Ti Al合金中得到应用。研究人员发现,孪晶能够强化固溶强化的镍合金;同时,有学者发现镍基高温合金中退火孪晶界对位错运动有明显的阻碍作用。因此,微孪晶化有望成为一种强化镍基高温合金的方法。本文归纳了镍基高温合金中微孪晶形成机制的发展和演变,分析了不全位错、内禀层错、外禀层错、复杂层错、元素偏析以及柯氏气团(Cottrell atmospheres)在微孪晶化中所起的作用,同时也阐述了孪晶界面处元素偏析在孪晶长大中的作用。此外,本文还综述了微孪晶在镍基高温合金强化中的作用,指出了通过微孪晶强化高温合金过程中存在的问题,展望了微孪晶在高温合金强化中的应用,为研究高温合金的中温变形机制和孪晶强化机制提供参考。     

弥散强化Pt-10Rh合金高温微观组织结构研究

用金相显微镜、扫描电镜观测普通Pt-10Rh合金和弥散强化Pt-10Rh合金的微观组织结构,结果表明,普通Pt-10Rh合金在高温下晶粒长大趋势明显,且高温持久性低,而弥散强化Pt-10Rh合金中有强化颗粒氧化锆的存在,能减少晶界缺陷,提高晶界结合力,降低晶界的扩散速度,减缓位错攀移,有效阻止晶粒长大和晶界的滑移,从而提高材料的强度和使用寿命。     

无取向硅钢中硫化物的析出机理

结合无取向硅钢中硫化物的析出热力学、动力学计算和扫描电镜(SEM)、透射电镜(TEM)检测,系统研究了硫化物在无取向硅钢中的析出机理,并讨论了硫化物对退火过程中晶粒长大的影响.结果表明,无取向硅钢中硫化物以(Mn,Cu)S复合析出相为主.在凝固过程中,MnS和Cu2 S均不具备析出热力学条件.MnS先于Cu2 S在晶界形核,随着温度的降低将以位错形核为主.在均热过程中,w(Si+Al)≥2.5％的无取向硅钢中的MnS和w(Si+Al)≤1.6％的无取向电工钢中的Cu2 S主要在晶界形核.同时,均热过程中MnS在晶界的析出量远大于Cu2 S,Cu2 S主要在后续的热处理过程中析出.MnS和Cu2 S的Ostwald熟化研究表明,w(Si+Al)≥2.5％无取向硅钢中的MnS和Cu2 S对晶粒长大的影响明显大于w(Si+Al)≤1.6％无取向电工钢.     

高压扭转大塑性变形Al–Mg合金中的晶界结构*

利用透射电镜和高分辨透射电镜(HRTEM)研究了高压扭转大塑性变形纳米结构Al–Mg合金中的位错和晶界结构。结果表明: 对尺寸小于100 nm的晶粒, 晶内无位错, 其晶界清晰平直; 而尺寸大于200 nm的大晶粒通常由几个亚晶或位错胞结构组成, 局部位错密度可高达10¹⁷ m^-2, 这些位错往往以位错偶和位错环的形式出现。用HRTEM观察到了小角度及大角度非平衡晶界、小角度平衡晶界和大角度Σ9平衡晶界等不同的晶界结构。基于实验结果, 分析了局部高密度位错、位错胞和非平衡晶界等在晶粒细化过程中的作用, 提出了高压扭转Al–Mg合金的晶粒细化机制。     

Exudation of Ag and Cu in internally oxidized Ag-Sn-In-(Cu) alloys

Growth and structure of pure Ag layers are investigated on the surface and at grain boundaries of Ag alloys that have been internally oxidized. Two Ag-Sn-In and an Ag-Sn-In-Cu alloy were studied by ion polishing, field emission scanning electron microscopy and optical microscopy. As already known from previous studies Ag atoms diffuse towards the surface. In the present study it is shown that grain boundaries can act as a sink for diffusing Ag atoms in competition with the surface. In the quaternary alloy Ag and Cu diffuse towards the surface simultaneously. The Cu diffusion is confined by the nucleation of CuO particles. The progress of the internal oxidation front is discussed in conjunction with the nucleation of pure Ag crystallites and CuO particles at grain boundaries.     

Morphology and orientation evolution of Cu6Sn5 grains on (001)Cu and (011)Cu single crystal substrates under temperature gradient

The morphology and orientation evolution of Cu6Sn5 grains formed on (001)Cu and (011)Cu single crystal substrates under temperature gradient (TG) were investigated.The initial orientated prism-type Cu6Sn5 grains transformed to non-orintated scallop-type after isothermal reflow.However,the Cu6Sn5 grains with strong texture were revealed on cold end single crystal Cu substrates by imposing TG.The Cu6Sn5 grains on (001)Cu grew along their c-axis parallel to the substrate and finally merged into one grain to form a fully IMC joint,while those on (011)Cu presented a strong texture and merged into a few dominant Cu6Sn5 grains showing about 30° angle with the substrate.The merging between neighboring Cu6Sn5 grain pair was attributed to the rapid grain growth and grain boundary migration.Accordingly,a model was put forward to describe the merging process.The different morphology and orientation evolutions of the Cu6Sn5 grains on single crystal and polycrystal Cu substrates were revealed based on crystallographic relationship and Cu flux.The method for controlling the morphology and orientation of Cu6Sns grains is really benefitial to solve the reliability problems caused by anisotropy in 3D packaging.     

Room-temperature diffusion-induced grain boundary migration in the fine-grained Pd side of CuPd diffusion couples

Transmission election microscopy (TEM) and Auger electron spectroscopy (AES) were used to study interdiffusion between fine-grained $\text{(≈150}\text{A}\text{?}\text{)}$ Pd films and Cu substrates. TEM demonstrated that a fine-grained alloy having a constant composition (65% CuPd) is formed at room temperature in the Pd side of the couple. Furthermore, the alloy grains are epitaxial to Pd grains at the interface region. The alloy phase is formed by the so-called diffusion-induced grain boundary (GB) migration. The diffusion of Cu atoms into Pd grain boundaries causes the epitaxial nucleation of the alloy phase on the side of the Pd GBs. The alloy phase then grows into the other face, while maintaining the high diffusive nature of the original GBs. The estimated size of the alloy phase was in good agreement with published GB diffusivity data for the diffusion of Cu into Pd GBs.     

The measurement of interfacial energies for solid Sn solution in equilibrium with the Sn–Bi–Ag liquid

The equilibrated grain boundary groove shapes of solid Sn solution in equilibrium with Sn–Bi–Ag liquid were observed from a quenched sample by using a radial heat flow apparatus. The Gibbs–Thomson coefficient, solid–liquid interfacial energy, and grain boundary energy of the solid Sn solution were determined from the observed grain boundary groove shapes. The thermal conductivity of the solid phase for Sn-10 at.%Bi-2 at.%Ag alloy and the thermal conductivity ratio of the liquid phase to the solid phase for Sn-10 at.%Bi-2 at.%Ag alloy at the melting temperature were also measured with a radial heat flow apparatus and a Bridgman-type growth apparatus, respectively. A comparison of present results for solid Sn solution in the Sn–10 at.%Bi–2 at.%Ag alloy with the results obtained in previous works for similar solid Sn in equilibrium with different binary or ternary liquid was made. From the comparison, it can be concluded that for solid Sn solution in equilibrium with different liquid, the Gibbs–Thomson coefficient seems to be constant and does not depend on the composition of liquid but solid–liquid interfacial energy changes little bit with composition of liquid at a constant temperature.     

超塑性变形微观结构变化的研究

本文研究了A1-10Si-1Mg合金在超塑性拉伸过程中微观组织的变化。揭示出该合金在超塑性变形中随应变量增加,晶内位错密度增加,是由两方面原因造成的:一是晶粒长大和晶界上第二相粒子给晶界滑移造成困难,使晶内位错调节作用增强;二是晶粒内的第二相粒子阻碍了晶内位错运动使位错堆积在第二相粒子周围。     

First-principles study on the effect and magnetism of iron segregation in Cu grain boundary

The atomic configurations and electronic structures of iron on CuΣ5 symmetrical tilt grain boundary (GB) have been studied based on the density functional theory. Different segregation positions of iron are considered. A weak tendency of iron segregating to GB is arrived due to the segregation energy. In addition, iron segregation shows a cohesion strengthening effect of Cu GB according to Rice–Wang model, which is mainly contributed by the charge redistribution. Finally, an enhancement of the local magnetic moment of iron in Cu GB or bulk or surface is explored due to larger atomic volume than the FCC iron crystal and the Cu atoms surrounding iron are slightly polarized by the doped iron. This study can enrich the understanding of the effects of iron on the cohesion of Cu–Fe alloy and also might supply an indirect guidance to expand the application of Cu–Fe alloy in electronic device manufacture field.     

压铸(Al63Cu25Fe12)p/AZ91复合材料的组织、性能和热处理特征

在CO2/SF6气氛保护下,采用压铸的方法将-200目的Al63Cu25Fe12准晶粉末注入到熔融的AZ91镁合金中,于720℃和一定的压力下保压30min,制备了新型的(Al63Cu25Fe12)p/AZ91镁基复合材料.结果表明,在复合过程中,准晶相分解出的自由Cu向基体扩散并与基体中的Al发生反应,生成的金属间化合物分布在准晶颗粒周围,同时Mg向颗粒中浸渗填充到颗粒的孔隙中;复合材料具有不同于基体镁合金的固溶时效特征,需要更长的时间才能达到时效峰值;复合材料经过热挤压和热处理后的力学性能显著提高,抗拉强度从AZ91铸态材料的189.54MPa提高到359.38MPa,但塑性有所降低.     

Microstructural evolution,mechanical properties and corrosion behavior of as-cast Mg-5Li-3Al-2Zn alloy with different Sn and Y addition

Influences of Sn and Y on the microstructure,mechanical properties,and corrosion behavior of as-cast Mg-5Li-3Al-2Zn (LAZ532) alloy were investigated.The addition of Sn and Y refines grains and results in the formation of Mg2Sn and Al2Y phases,thus improving the mechanical properties of alloy by second phase strengthening and grain refinement strengthening.As-cast LAZ532 alloy shows typical filiform corrosion morphology,and the addition of Sn and Y does not change the corrosion mode of alloy.Ascast LAZ532-0.8Sn-1.2Y alloy shows excellent mechanical properties with yield strength of 166.2 MPa,ultimate tensile strength of 228.6 MPa and elongation of 14.8 ％,and exhibits the best corrosion resistance with the smallest corrosion current density and the lowest anodic dissolution rate.     

The activation areas for grain boundary sliding

The activation areas for grain boundary sliding in Al, Pb, Sn, Zn, and Cu are compared with those for creep in the same materials. It is found that the activation area-stress relation for grain boundary sliding is similar to that for creep. This observation is consistent with a dislocation or ledge mechanism of grain boundary sliding.