Effect of Rapid Solidification on Structure and Properties of Some Lead-Free Solder Alloys

Four of the binary lead-free solder alloys of compositions Sn-0.5Cu, Sn-3.5Ag, Sn-5Sb and Sn-9Zn, were rapidly solidified by melt-spinning technique as a technique for producing new alloy compositions. The results show that rapid solidification causes formation of some intermetallic compounds such as Ag₃Sn and Cu₆Sn₅ in the two alloys Sn-3.5Ag and Sn-0.5Cu, which cannot be formed at the equilibrium phase diagram at these compositions; contraction in the volume of the unit cell of the tetragonal Sn; reduction of the melting points due to the decrease in the crystalline size of Sn matrix; and formation of some vacancies in the resulting alloys, which cause reduction of the measured density than that calculated by mixture rule and increase the electrical resistivity.     

凝固条件对非晶合金的微观结构和性能的影响

采用不同凝固控制的方法,研究了凝固条件对非晶合金的微观结构、热稳定性以及力学性能的影响。研究表明,高温下铜模喷铸样品为完全非晶结构,而低温喷铸和电弧原位吸铸所制备的样品中存在着一些纳米量级的析出相。高温喷铸样品表现出非晶合金典型的脆断行为,但低温喷铸和原位电弧吸铸样品则表现出较高的强度和良好的塑性变形能力。高温甩带样品初始晶化温度高于相应的低温甩带样品,其长期热稳定性优于低温甩带样品,表明浇铸温度的升高增强了非晶合金的热稳定性。     

Mechanical and Abrasive Wear Properties of Anodic Oxide Layers Formed on Aluminium

Aluminium oxide coatings were formed on aluminium substrates in oxalic acid-sulphuric acid bath.Abrasion tests of the obtained anodic layers were carried out on a pin-on-disc machine in accordance with the ISO/DP 825 specifications.The Vickers microhardness,D(HV0.2),and the abrasion weight loss,Wa(mg) were measured.Influence of oxalic acid concentration(Cox),bath temperature(T) and anodic current density(J) on D and Wa has been examined,and the sulphuric acid concentration(Csul) was maintained at 160 g·L-1....     

Effect of Multi-Wall Carbon Nanotubes on the Mechanical Properties of Natural Rubber

Multi-walled carbon nanotubes (MWNTs) were used to prepare natural rubber (NR) nanocomposites. Our first efforts to achieve nanostructures in MWNTs/NR nanocomposites were formed by incorporating carbon nanotubes in a polymer solution and subsequently evaporating the solvent. Using this technique, nanotubes can be dispersed homogeneously in the NR matrix in an attempt to increase the mechanical properties of these nanocomposites. The properties of the nanocomposites such as tensile strength, tensile modulus, elongation at break and hardness were studied. Mechanical test results show an increase in the initial modulus for up to 12 times in relation to pure NR. In addition to mechanical testing, the dispersion state of the MWNTs into NR studied by Transmission Electron Microscopy (TEM) in order to understand the morphology of the resulting system     

凝固速率对Si-Ta合金固液界面稳定性的影响

以Si-Ta合金为研究对象,采用零功率法研究凝固速率对定向凝固固液界面稳定性的影响.结果表明:当凝固速率在0.3～9.0mm/min范围内,随着凝固速率的增大,固液界面经历了平界面→浅胞状界面→锯齿状界面→浅胞状界面→平界面的演化规律.在较低的凝固速率范围之内,实验结果与理论计算基本吻合.然而,在较高凝固速率时,实验结果与理论计算出现偏差,这是由于热力学和动力学均发生变化,使得在凝固速率V=5.0mm/min时固液界面就已经达到了稳定的平界面.     

Ce对Al-Zn-Mg-Cu合金亚快速凝固铸造组织的影响

通过XRD,DSC,SEM,EDS等现代分析方法,研究了稀土元素Ce在不同凝固冷却速率下对Al-Zn-Mg-Cu合金显微组织、凝固温度的影响,分析讨论了Ce对合金晶粒细化和熔体净化作用的原理。结果表明,合金的主要析出相为α-Al和MgZn_2型共晶相,MgZn_2固溶了Al,Cu,Mg等元素并形成了Mg(Zn,Cu,Al)_2相,在晶界上溶质元素浓度较高,与α-Al基体共晶形成层片状共晶组织。添加Ce能使合金枝晶间距减小,并减小共晶层片间距和细化共晶组织,显著细化晶粒,并抑制铝合金中的杂质相Al7Cu2Fe的出现。Ce还将合金α-Al基体和共晶相的析出温度分别降低了6.4℃和5.6℃。     

Effect of Melt Superheating Treatment on Directional Solidification Interface Morphology of Multi-component Alloy

The influence of melt superheating treatment on the solid/liquid (S/L) interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteristic and S/L interface stability. The results indicate that the interface morphology is not only related to the withdrawal velocity (R) but also to the melt superheating temperature (Ts) when the thermal gradient of solidification interface remains constant for different Ts with appropriate superheating treatment regulation. The interface morphology changes from cell to plane at R of 1.1 μm/s when Ts increases from 1500°C to 1650°C, and maintains plane with further elevated Ts of 1750°C. However, the interface morphology changes from coarse dendrite to cell and then to cellular dendrite at R of 2.25 μm/s when Ts increases from 1500°C to 1650°C and then to 1750°C. It is proved that the solidification onset temperature and the solidification interval undergo the nonlinear variation when Ts increases from 1500°C to 1680°C, and the turning point is 1650°C at which the solidification onset temperature and the solidification interval are all minimum. This indicates that the melt superheating treatment enhances the solidification interface stability and has important effect on the solidification characteristics.     

凝固速度对镁合金阳极组织与性能的影响

以Mg-Hg-X合金为研究对象,利用金相显微镜、扫描电子显微镜、电化学测试仪等研究了不同铸造凝固速度对镁合金阳极经混合酸侵蚀后显微组织、电化学性能和腐蚀速率的影响.结果表明,Mg-Hg-X合金中Mg、Hg形成的第二相化合物组成随合金铸造凝固速度变化而改变,缓慢凝固主要形成Mg3Hg相,快速凝固主要形成Mg2Hg相;同时随铸造凝固速度加快,Mg-Hg-X合金材料腐蚀速率有所降低,电极电位正移.     

快速凝固Cu基液相不混溶合金的研究现状

概述了快速凝固技术制备液相不混溶Cu基合金的国内外研究现状,主要从快速凝固组织、液相分离机制、形核和生长动力学3方面展开阐述,并指出了今后液相不混溶合金的研究方向。     

Solidification Behavior of Immiscible Alloys under the Effect of a Direct Current

Directional solidification experiments were carried out with Al-Pb alloys under the effect of a direct current （DC）. The experimental results show that the DC causes a migration of the minority phase droplets （MPDs） from the middle part to the surface region of the sample, Samples with either a finely dispersed microstructure or a shell/ core structure were obtained by solidifying the alloy under the effect of the properly selected DC densities, A model was developed to describe the microstructure evolution in an immiscible alloy directionaliy solidified under the effect of the DC. The microstructure formation in the AI-Pb alloys was calculated. The numerical results are in favorable agreement with the experimental ones. They demonstrate that the DC affects the microstructure formation mainly through changing the spatial motions of the MPDs and the temperature field of the melt in front of the solid/liquid interface. The formation mechanisms of the finely dispersed microstructure as well as the shell/core structure were sufficiently clarified.     

合金化对定向凝固Ti-AI-Nb合金微观结构与力学性能的影响

采用定向凝固方法制备了Cr/Mo微合金化高Nb Ti-Al合金,并考察了其微观结构和力学性能.结果表明,两种合金都呈现出层片状微观组织.尽管温度梯度受限,抽拉速度较高,但与Ti-16A1-12Nb相比,Ti-16A1-12Nb-3Cr-1Mo合金中的片层倾向于与抽拉方向呈更小角度生长,在室温和650℃时的拉伸强度和塑性...     

挤压温度对高硅铝合金材料力学性能的影响

针对航空航天电子封装用轻质高硅铝合金材料,采用空气雾化水冷与真空包套热挤压工艺相结合的方法,制备了Al-30Si和Al-40Si过共晶高硅铝合金材料,并通过金相显微镜观察了材料的微观组织,测定了合金材料的抗拉强度以及延伸率,对拉伸试样的断口进行了扫描.探讨了挤压温度对材料组织、强度、延伸率及断裂行为的影响.结果表明:利用粉末冶金热挤压技术所制备的高硅铝合金材料,其硅相细小,当挤压温度为370℃时,其硅相大小为2～10μm,且分布均匀弥散;硅相尺寸随着挤压温度的升高而长大;抗拉强度随挤压温度的升高而降低,Al-30Si经370℃挤压后,其室温抗拉强度为239MPa,而550℃为206MPa;延伸率随挤压温度的升高而有所增加,但不很敏感;随挤压温度的升高,材料的断裂方式由单纯的韧性断裂逐渐向韧性与脆性共存的混合断裂方式转变.     

温度梯度对定向凝固Al-4.5%Cu合金一次枝晶间距的影响

使用5kg坩埚下拉式定向凝固设备,对Al-4.5%Cu合金进行定向凝固试验,研究Al-4.5%Cu合金在不同温度梯度下一次枝晶间距的变化规律。结果表明:在其他凝固参数不变时,随着温度梯度的增大,一次枝晶逐渐变小,细密,挺直,基本呈平行状分布,同时计算的一次枝晶间距值与Hunt模型计算值接近,实验测得的一次枝晶间距的回归曲线为:y=2843478.3x2-70217.4x+543.8。用温度梯度较高的实验值来模拟时,可得到1λ=26.7G-0.5-135.9,一次枝晶间距λ1与G-0.5基本呈线性关系,这和Hunt模型分析结果一致。     

Interactive Effect of Grain Orientation and Grain Size on Magnetic Properties of Fe-78 wt% Ni Ribbons

Fe-78 wt% Ni ribbons were prepared by the melt spinning technique and the interactive contribution of the grain size and grain orientation on the magnetic properties was examined. Heat treatment at 673 K for 1 h followed by furnace cooling was performed to show the annealing impact. At three wheel speeds of 10, 20, and 30 m/s, the saturation magnetization nearly does not change. High wheel speed and heat treatment are inclined to promote the growth of <001> grains. Although the <001> orientation is not the easy axis of magnetization, the improvement of the texture in this direction makes the coercivity decrease, which counteracts the inverse effect of the grain size at high wheel speed. It indicates that for preparing soft magnetic ribbons, the interactive contribution of grain orientation variation and the grain size should be considered.     

Inkjet printing of conductive Ag lines and their electrical and mechanical characterization

This paper aims to investigate the effects of the substrate, the printed line thickness and the sintering temperature on the electrical resistivity, Young's modulus and hardness of inkjet-printed Ag thin films. Electrical resistivity was determined from the four-point method and Young's modulus and hardness were evaluated from nanoindentation test. Several models for evaluating Young's modulus and hardness were used and compared to account for the influence of substrates. It is noted that Ag lines on glass have higher resistance and resistivity than those on polyimide (PI) since Ag lines on glass and PI have tensile and compressive residual thermal stresses, respectively, due to the difference of coefficient of thermal expansion between Ag lines and substrates. Young's modulus of Ag films on glass can be predicted by the modified King and Bec models considering the substrate effect, but these models offer unstable results for Ag films on PI. Young's modulus and hardness of Ag films increase with the sintering temperature, and they are little affected by the film thickness when fully sintered.     

Competitive Nucleation and Rapid Growth of Co-Si Intermetallic Compounds during Eutectic Solidification under Containerless Processing Condition

The liquid-solid transitions of (Co2Si+CoSi) and (CoSi+CoSi2) eutectic alloys were realized in drop tube and the rapid eutectic growth mechanism of intermetallic compounds was examined. The experimental and calculated results indicate that with increasing Co content, the intermetallic compound prefers nucleating primarily. The eutectic microstructures experience the transitions of ’lamellar-anomalous-divorced’ eutectic with undercooling. In undercooled state, the growth of CoSi intermetallic compound always lags behind others, and no matter how large the undercooling is, this intermetallic compound grows under the solutal diflusion control. The calculated coupled zone demonstrates that (Co2Si+CoSi) eutectic can form within certain undercooling regime, when the composition is in the range from 23.6% to 25.4% Si. And the calculated coupled zone of (CoSi+CoSi2) covers a composition range from 40.8% to 43.8% Si.     

相场模型凝固组织模拟进展

本文对相场模型的物理本质、数值计算方法以及在凝固微观组织模拟中的应用和进展进行了综述,并指出相场模型凝固微观组织模拟的发展方向。     

单相合金快速凝固组织形成原理及应用

回顾了固液界面形态稳定性理论,分析了单相合金快速凝固组织形成的原理,最后介绍了快速凝固技术的最新应用。     

快速凝固锌铝合金微观形貌研究

利用单辊急冷法制备了一种锌铝合金，通过XRD分析表明，合金相组成主要为过饱和相α’和富锌相η，以及微量的介稳定相ε-CuZn4。ESEM及TEM观察结果发现，快速凝固所得合金晶粒为等轴晶，并且极其细化，甚至达到纳米级别，其中Si元素以特殊圆薄片状单质存在，较高含量的Si元素未出现偏析，均匀分散在基体中。