Novel rare-earth-containing lead-free solders with enhanced ductility

Severallead-free material systems are availableas replacements for traditional lead-based solders in microelectronic packaging, including near-eutectic combinations oftin-rich alloys. Although these materials have superior mechanical properties as compared to the Pb-Sn system, much work remains in developing these materials for electronic packaging. Small additions of rare-earth elements have been shown to refine the microstructure of several lead-free solder systems, thus improving their mechanical properties. This study investigated the effect of the addition of lanthanum on the melting behavior, microstructure, and shear strength of an Sn-3.9Ag-0.7Cu alloy. The influence of LaSn₃ intermetallics on microstructural refinement and damage evolution in these novel solders is discussed.     

稀土在铝合金表面处理中的应用及研究进展

评述了稀土在铝合金表面处理中的应用及研究进展,尤其是铝合金稀土表面转化膜技术和稀土对铝合金阳极氧化的影响两方面.稀土表面转化膜能够提高铝合金的耐蚀性能,工艺以化学浸泡为主;稀土对铝合金阳极氧化是有益的:它使铝合金接受极化的能力增强,同时提高氧化膜的抗蚀性.因此,稀土应用于铝合金表面处理具有良好的发展前景.     

Recent developments in the research of shape memory alloys

Most of shape memory alloys are functional intermetallics. They are now practically being used for couplings, actuators, medical guide wires etc., and are hopeful candidates for smart materials, which already exist. In the present paper, recent developments within nearly 10 years on shape memory alloys and martensitic: transformations, on which shape memory effect and superelasticity are based, were concisely reviewed. Since Ti–Ni alloys are the best practical shape memory alloys, we mostly discussed on the alloys, but we discussed more general problems as well. Furthermore, we discussed the ductility and density of point defects in intermetallics, since they are important problems in intermetallics in general. At the end we introduced some recent applications of shape memory alloys briefly.     

高温结构金属间化合物及其强韧化机理

综述了自1988年以来中国科学院高温合金和金属间化合物研究组(郭建亭研究组)在高温结构金属间化合物NiAl及其合金、Ni3Al及其合金、FeAl和Fe3Al及其合金、TiAl合金以及金属间化合物环境脆性方面的主要研究成果:NiAl合金超塑性的发现及其机理研究;稀土元素改善NiAl合金的室温塑性和高温抗氧化性能;NiAl合金的韧脆转变行为及其机理;纳米晶NiAl合金及其复合材料的强韧化;内生颗粒增强NiAl基复合材料及强韧化机制;NiAl合金良好的耐高温摩擦磨损性能及自润滑机理的发现;NiAl中合金元素的作用与JJ-3合金的发展;在国际上首先发现适量Zr可韧化无硼Ni3Al合金;为使Ni3Al强韧化硼含量应加至溶解度附近;FeAl合金反常屈服峰的发现及其机理研究;微量Mg可明显改善FeAl和Fe3Al合金的室温塑性;TiAl-W-Si合金的组织、相转变和界面精细结构;金属间化合物的环境脆性实质是氢致脆性;在国际上首先用第一原理方法(DVM)研究了L12型CO3Ti的环境脆性.     

机械合金化热压烧结Mo-Si-B多相难熔合金的超塑性

采用机械合金化(MA)+热压烧结制备Mo-9Si-8B-3Hf难熔合金,研究了球磨时间对热压合金致密度的影响.采用真空高温拉伸实验评价了Mo-Si-B难熔合金的高温性能.结果表明,Mo-Si-B难熔合金的致密度随着球窘时间的延长而增大.制备的合金由连续分布的Mo固溶体(α-Mo),Mo3Si和Mo5SiB2组成.各物相...     

Some particularities of the corrosion behaviour of Mg-Zn-Mn-Si-Ca alloys in alkaline chloride solutions

The influence of silicon and calcium on corrosion behaviour of Mg-6Zn-Mn alloys was investigated in alkaline solutions. The corrosion behaviour of the alloys with varied silicon and calcium content mainly depends on volume fractions and morphology of the intermetallics. In Cl-ion-free solutions silicon increased the corrosion resistance of alloys causing the growth of the surface passive film mostly composed of hydroxide products. Calcium had caused trouble to the formation of the stable protective film through the formation of Ca-Mg-Si intermetallics. In Cl-ion containing solutions intermetallic Ca-Mg-Si phase was responsible for extreme initial corrosion of Mg-6Zn-Mn-Si-Ca alloys.     

Three-dimensional characteristics of Fe-rich intermetallics in gravity-cast Al-6Si alloys

Fe-rich intermetallics, especially β-Fe phase, usually forming in the microstructure of cast aluminum alloys, are very detrimental to mechanical properties. In the present work, the effects of Fe content on phase transformation and microstructures were analyzed using a 3D X-ray microscope. Based on the high-resolution 3D X-ray computed tomography, the 3D characteristics of Fe-rich intermetallics and micropores in the gravity-cast Al-6Si alloys with different Fe contents were investigated. In addition, the effect of intermetallics on the microporosity was discussed. The results show that with increasing the Fe content from 0.10wt.% to 0.60wt.%, the volume fraction of Fe-rich intermetallics and the volume of the largest size Fe-rich intermetallic increased, and the 3D morphology of intermetallics changed from fine flake to network aggregation. As the Fe contents increased, the shrinkage pores were characterized, which were rather complex due to the micropores promoted by the intermetallics interactions.     

Using Amorphous Phases in the Design of Structural Alloys

The recent discovery that amorphous alloy powders can be prepared by mechanically alloying a mixture of pure crystalline intermetallics is opening new windows to the synthesis of engineering materials. Amorphous powders synthesized by mechanical alloying may find application in the design of structural alloys, high thermal conductivity alloys, and metal-matrix composites.     

细化及变质方法对A356铝合金微观组织的影响

在对比研究细晶铝锭和铝钛中间合金2种不同加钛细化方法的基础上,研究锶、稀土、锶 稀土不同变质方法处理后A356铝合金的铸态微观组织变化。结果表明:细晶铝锭细化效果较铝钛中间合金好,经细晶铝锭 锶 稀土联合处理的A356铝合金,晶粒细小,变质充分,针孔较少,组织均匀,是一种优良的细化变质方法。     

医用稀土镁合金微观组织特征及力学行为研究进展

近年来,镁合金作为生物医用金属材料受到了广泛关注,但其较差的力学强度极易导致植入物在服役周期内崩塌断裂,严重危及患者生命安全。稀土微复合金化作为当下提高可降解镁合金力学性能的有效措施,在消除镁合金杂质元素、净化熔体的同时,还可以起到促进动态再结晶、形成长周期堆垛有序相等作用。因此,本文从稀土镁合金微观结构转变及其与力学性能的基本关联出发,综述了近年来医用稀土镁合金组织特征及力学性能的研究进展,深入发掘了稀土元素、第二相及镁合金力学性能之间的本质关联,详细阐述了连续动态再结晶对稀土镁合金的强韧化机理,全面叙述了稀土元素诱导长周期堆垛有序结构对镁合金力学性能的影响规律。最后,本文对医用稀土镁合金未来的发展方向进行了展望。     

High-Efficiency Inhibition of Gravity Segregation in Al–Bi Immiscible Alloys by Adding Lanthanum

The inhibition of gravity segregation has been a long-standing challenge in fabrication and applications of homogeneous immiscible alloys. Therefore, the effect of rare-earth La on the gravity segregation of Al–Bi immiscible alloys was investigated to understand the homogenization mechanism. The results showed that the addition of La can completely suppress the gravity segregation. This is attributed to the nucleation of Bi-rich liquid phase on the in-situ produced LaBi₂ phase and the change of the shape of LaBi₂@Bi droplets. In addition, a novel strategy is developed to prepare the homogeneous immiscible alloys through the addition of rare-earth elements. This strategy not only is applicable to other immiscible alloys, but also is conducive to finding more elements to suppress the gravity segregation. This study provided a useful reference for the fabrication of the homogeneous immiscible alloys.     

Mechanical properties and oxidation characteristics of TiNiAl(Nb) intermetallics

The structural evolution, mechanical properties and the oxidation characteristics of Ti₅₀Ni_50−xAl_x alloys were investigated. The influence of additive Nb on the microstructure, mechanical properties as well as the high temperature oxidation resistance was examined. It is found that the substitution of Al for Ni can remarkably reinforce the TiNi-based intermetallics by precipitation of (Ti,Al)₂Ni phase and by solid-solution strengthening effects. It is also found that the addition of Nb has beneficial influence on the mechanical properties of TiNiAl intermetallics, and that the oxidation resistance of TiNiAl(Nb) alloys can be effectively improved by the Nb addition. The effect of Nb on the high temperature oxidation behavior of TiNiAl(Nb) alloys has been discussed.     

Effect of Melt Homogeneity on the Age-hardening of Copper-Chromium Alloys

Abstract

Copper-chromium alloys are treated with rare earths to impart higher homogeneity within the melts. The age-hardening behaviour of the alloys are studied and are compared with the alloy without rare-earth treatment. Also, copper chromium alloys are subjected to vibration during solidification to induce a greater structural fineness. The ageing behaviours of the vibrated alloys are compared with those of the rare-earth treated alloys. It is observed that rare-earth treatment leads to finer dispersion of chromium precipitates. It is noted that higher strength properties at a relatively high level of conductivity are achievable in rare-earth-treated alloys. Also, superimposition of vibration during solidification of copper-chromium is found to have led to higher aged hardness with a fall in conductivity.     

Effects of rare earths on friction and wear characteristics of magnesium alloy AZ91D

The influence of various rare-earth contents on the friction and characteristics of magnesium alloy AZ91D was studied.The results show that the wear r5esistance properties of rare-earth magnesium alloys are better than those of the matrix alloy under the testing conditions.Magnesium alloys undergo transition from mild wear to severe wear.The addition of rare earths refines the structure of alloys,improves the comprehensive behaviors of the magnesium alloys,increases the stability of oxidation films on worn surfaces,enhances the loading ability of rareearth magnesium alloys,and delays the transition from mild wear to severe wear effectively.     

Pt-24Ir-RE合金的显微组织与性能研究

通过金相及电子显微镜技术，进行了力学和电学性能实验，研究了添加微量稀土元素La、Sm、Y对Pt-24Ir合金的组织结构与性能的影响。结果表明：稀土元素有效地细化了合金的显微组织结构，并以单质形式均匀析出和弥散分布在合金基体中，从而使合金的综合性能获得改善。     

金属间化合物对高温合金强化机理的研究

研究了金属间化合物对高温合金材料的强化作用,在CrWMoV合金中添加Al和Ni可以形成Ni-Al,Fe-Al和W－Al系等金属间化合物,在合金中起到弥散强化作用和抗氧化作用,能提高合金的高温强度和冲击韧性,实验发现以2％Al的添加为最佳。     

The Effect of Alloying Elements on the Microstructure of Al-5Fe Alloys

The effects of adding Cr, Mn, and Zr on the microstructure of Al-5Fe alloys has been studied by metallographic analysis, scanning electron microscopy, x-ray diffraction analysis, and differential thermal analysis. It has been found that the effects of the different elements on the microstructure of ferro-aluminum intermetallics in Al-5Fe alloys are not alike. Addition of Cr in Al-5Fe alloys dissolves only into AlFe intermetallics, resulting in the morphology of the AlFe phases being changed with increasing Cr content. Cr is a favorable nucleating agent for encouraging metastable Al _x Fe (x = 4.6 to 5.0) phase formation. Adding Mn in Al-5Fe alloys may stabilize the metastable Al₆Fe phase, helping the primary phase field of Al₇Cr diminish or even disappear and forcing Cr to dissolve into AlFe phases. Adding Zr does not refine the primary AlFe intermetallics. Al₃Zr particles in Al-5Fe alloys will occupy the growing spaces of ferro-aluminum phases and indirectly hinder the growth of Fe-bearing phases.     

Recent advances in the synthesis of alloy phases by mechanical alloying/milling

Mechanical alloying (MA) is a solid-state powder processing technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened nickel- and iron-base superalloys, MA has now been shown to be capable of synthesizing a number of alloy phases—equilibrium and supersaturated solid solutions, stable and metastable crystalline and quasicrystalline intermediate phases, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and displacement reactions have been critically reviewed. Wherever possible, comparisons have been made on the product phases obtained by MA and by rapid solidification processing, another non-equilibrium processing technique.     

Ternary iron alloys for permanent magnetic materials

Iron-based rare-earth ternary alloys with a high energy product came into prominence recently as permanent magnetic materials. Also, a large number of iron-based ternary phase diagrams were critically evaluated and published recently as monographs under the auspices of the International Programme for Alloy Phase Diagram Data. This review presents a brief comparison of the data on crystal structures of ternary compounds and the corresponding phase diagrams for a number of ternary iron rare-earth (RE) X series: B-Fe-RE, C-Fe-RE, Fe-N-RE, Al-Fe-RE, Co-Fe-RE, Fe-Ni-RE, and Fe-RE(1)-RE(2). It is hoped that this exercise will aid in pinpointing discrepancies and planning future investigations on ternary compounds and phase equilibria in unexplored systems.