具有液-液相分离性质的Bi60Ga40合金熔体黏滞性的研究

通过对Bi60Ga40合金熔体的黏度的系统测量和分析,研究了Bi60Ga40合金熔体的黏度随温度变化的规律和熔体结构的变化.结果表明,Bi60Ga40合金熔体的黏度随温度的变化呈明显的不连续性,根据黏度的变化可以将熔体状态分为高温区、中温区和低温区,各温区间存在黏度突变温度区间.DSC进一步验证了Bi60Ga40熔体在620,-650℃之间发生了结构突变,在260～290℃之间由于液.液相分离引起了结构突变.文中对试验结果进行了讨论.     

液态Ga的密度和黏度及其微观结构

通过测量Ga熔体的密度和黏度,研究了液态Ga密度和黏度随温度的变化规律及其熔体微观结构的变化。Ga熔体的密度-温度关系曲变化表明,密度随着温度的升高而降低,但宏观体积增大;Ga熔体的黏度随着温度的降低而增加,总体上呈现指数规律,在180~210℃之间存在突变点。     

由形核过冷度研究Ga熔体原子团尺寸变化的滞后性

DSC测试表明,Ga的形核过冷度随其熔体高温保温时间的延长而增大,随熔体降温后保温时间的延长而减小,表现出明显的滞后性.通过对熔体温度与熔体中原子团尺寸之间关系的热力学和动力学研究,得到了金属熔体原子团中的原子数随温度变化的关系式,获得了确定熔体温度变化后其形核温度变化滞后幅度的方法,确定的Ga的形核温度变化滞后幅度与实验结果相吻合,其误差只有3.9%—4.8%.     

Ga-Sb合金熔体的黏滞行为

利用熔体黏度仪系统研究了不同成分Ga-Sb熔体的黏度变化规律。结果表明,Ga-Sb熔体的黏度总体趋势是随温度的降低而增大,黏度变化曲线基本呈指数变化。其中Ga36.5Sb63.5熔体黏度随温度的变化在830℃左右出现突变,将黏度曲线分成低温区和高温区两部分。根据该熔体结构变化的特点,对有关试验结果进行了分析讨论。     

热历史对In-55wt%Sb亚共晶合金熔体粘度的影响

利用回转振动粘度仪在液相线以上较大温度范围内,测量了In-55%Sb（质量分数）亚共晶合金熔体在不同的升降温过程中的粘度.实验结果表明,熔体经历的热历史对其粘度具有显著的影响.熔体在降温过程中的粘度高于升温过程中,在过热100℃后的降温过程中熔体的粘度较之无过热的降温过程中要低.在不同的热过程中,粘度发生转折变化的温度不同,在升温过程中,发生在850℃左右,在过热100℃和无过热的降温过程中,分别发生在750℃和650℃左右.熔体粘度的突变反映了熔体结构在相应温度的突然变化.     

电子束冷床熔炼TC4合金温度场模拟

利用ANSYS软件对电子束冷床熔炼TC4钛合金过程进行模拟研究.结果表明:熔体从冷床滴入坩埚之后,主要出现熔体升温、形成稳定熔池、熔体凝固、熔体温度下降和凝固结束这5个阶段.在开始熔炼时,熔体温度较低,升温也比较慢,但随着熔炼的进行,熔体升温加快,并维持在高温状态,最后熔体发生凝固降温,且降温速度很快.降温过程主要分为两个阶段,在快速降温阶段,熔体快速出现部分凝固,而在降温平衡阶段,熔体主要进行补缩.当降温时间达到500 s时,熔体温度基本保持不变.     

镓基合金凝固与熔化过程中的相变行为

通过DSC热分析技术研究了成分和升降温速率对GaInSn三元合金和GaIn二元合金的固-液相变行为的影响。结果表明,GaInSn三元合金和GaIn二元合金升温过程中的固-液转变(熔化)温度十分稳定,对成分波动不敏感;而降温过程中的液-固转变(凝固)温度则随成分的波动而显著变化。此外,讨论了Ga基合金过冷度与Ga含量和冷却速率之间的关系。     

Al-Si合金熔体热处理的结构转变

用示差扫描量热分析了Al-Si合金温度处理的熔体结构变化规律及结构变化温度。结果表明,在升温阶段的Al-7%Si亚共晶、Al-12%Si共晶及Al-20%Si过共晶合金的熔体中均存在额外的热效应,范围均在798～850℃之间,额外热效应温度范围与含硅量无关,结构转变焓值随合金的硅含量增加而增加,氢含量不影响结构转变的温度;而在降温过程中仅在Al-20%Si过共晶合金中发现了额外热效应,额外热效应的出现及温度范围取决于降温速度。分析认为,升温阶段的额外热效应体现了Al的熔体结构变化,降温阶段的额外热效应与熔体中的Si-Si原子团簇的行为有关。     

Al熔体粘度的突变点及与熔体微观结构的关系

通过测量Ａｌ熔体的粘度，研究了Ａｌ熔体粘度随温度的变化规律，发现在升温过程中熔体粘度值在７８０和９５０℃左右发生突变。在降温过程中，粘度的突变发生在９３０和７５０℃。Ａｌ熔体氢含量的测定表明，氢含量随温度变化曲线也在７８０℃发生突变。通过对液态Ａｌ的分子动力学模拟，发现Ａｌ的第一近邻配位原子的排布方式随温度的变化在７８０℃左右与９５０℃左右也存在突变。探索了Ａｌ熔体液态微观结构与熔体粘度的内在联系     

对回转式粘度仪测量结果影响因素的研究

液体的粘度是重要的基本物理参数和结构敏感物性参数。针对高温回转式粘度仪，对纯水、金属铜和锡熔体粘度测试过程中熔体容量、坩埚内表面粗糙度、保温时间、试样升温和降温以及试验气氛等因素对熔体粘度测定进行了研究。通过大量试验并与国际公认值比较，发现这些因素都在不同程度上影响着粘度测量值。     

ELECTRONIC STRUCTURE OF THE LaNi5-xGax INTERMETALLIC COMPOUNDS

The equilibrium structures and electronic structure of LaNi5-xGax （x=0, 0.5, 1.0） compounds have been investigated by all-electron calculations. Based on the full geometry optimization, the densities of states and electron densities of LaNi5-xGax are plotted and analyzed. It is clear that the substitution of Ga at the Ni site leads to a progressive filling of the Ni-d bands, the ionic interaction between Ni and Ni, with Ga plays a dominant role in the stability of LaNi5-xGax compounds. The smaller the shift of EF toward higher energy region, the more stable the compounds will be. The increased contribution of the Ni-d-Ga-d interactions near EF and the low energy metal-gallium bonding bands indicate that the compounds become more stable. The results are compared with experimental data and discussed in light of previous studies.     

热电池阳极材料Li—B合金的密度分析

根据Li-B化合物的六方结构模型，计算了热电池阳极材料Li-B合金随B含量变化的理论密度曲线。采用阿基米德方法分别测量了含24％（摩尔分数）B的Li-B合金反应完全并经冷挤压后的样品和未经第二次放热反应中间样品的密度，综合分析了以往不同研究者所测量的结果，结果表明，反应充分并消除合金中孔隙后合金的实验密度值与理论计算值一致，以往造成实验偏差的主要原因是样品中存在孔隙，中间样品的密度与Li-B元素混合计算密度一致，它支持在第一次反应和第二次反应之间B熔化在Li中的观点。     

A first principles study of the influence of alloying elements on TiAl: site preference

The electronic structure and binding energy of a number of TiAl-X alloy systems (X=V, Cr, Mn, Fe, Co, Ni, Y, Zr, Nb, Mo, Hf, Ta, W, Ga, Ge, In or Sb) were calculated using the discrete variational cluster method, based on the local density approximation of the density functional theory. The site preference of the ternary additions to TiAl was investigated by means of the binding energy data and the Bragg–Williams model. The results showed that Y, Zr, Nb, Mo and Sb preferentially occupy the Ti sublattice sites, Ga and In occupy the Al sublattice sites, while V, Mn, Cr, Co and Ge may occupy either site, depending on the Ti/Al ratio. Investigation of the total and local densities of states for representative elements showed that the substitution behaviour of ternary additions in TiAl is determined by the electronic structure of the systems. The present predictions of the site preference of alloying elements in TiAl show good agreement with the most recent experimental findings.     

The effect of growth rate on anodically formed zirconium oxide films

Anodic oxide films have been grown on zirconium at constant current densities for a range of current densities extending over several orders of magnitude. Optical and scanning electron microscopy have shown structural differences for different current densities and the mechanical failure of the films has been studied by tensile testing after oxidation. As the current density was reduced, blistering and breaking of the oxide layer was found to increase and this has been associated with anomalies in the experimental voltage-time graphs. The relationship between electric field in the oxide and the current density has been investigated and values of the activation energies of diffusion have been estimated for both oxygen ions and zirconium ions. Possible mechanisms are discussed for the stress relaxation found to occur increasingly for current densities from 0·01 to 1 mAcm^?2.     

First principles study of site substitution of ternary elements in NiAl

Site substitution of ternary elements in ordered compounds influences the electronic structure and hence the properties of compounds at the continuous level. The electronic structure and binding energy of a number of NiAl-X alloy systems (X=Ti, V, Cr, Mn, Fe, Co, Zr, Nb, Mo, Hf, Ta, W, Si, Ga, or Ge) were calculated using the discrete variational cluster method based on the local density approximation of the density functional theory. The site preference of the ternary additions to NiAl was investigated by employing the Bragg–Williams model to analyse the calculated binding energy. The results show that all the considered ternary elements possess stronger preference to the Al sublattice sites than a Ni atom does. A new method of identifying sublattice substitution of ternary additions in NiAl was proposed by comparison of the binding energies per atom of the ternary and the binary clusters involving the fourth nearest neighbours. The analysis suggests that Fe and Co atoms occupy the Ni sublattice sites, whereas Si, Ga and Ti atoms occupy the Al sublattice sites. The remaining elements may substitute for both sublattices: Mn is most likely to go for the Ni sublattice; V, Cr, Zr, Nb, Mo, Hf, Ta, W and Ge have a larger preference for the Al sublattice, but Cr and W do not show significant preference to any sublattice. The densities of states involving alloying additions of Co, Si and Cr were further investigated to clarify the site preference of the alloying additions.     

Influence of Ga and Hg on microstructure and electrochemical corrosion behavior of Mg alloy anode materials

The effects of Hg and Ga on the electrochemical corrosion behavior of Mg-5%Hg （molar fraction） alloys were investigated by the measurement of polarization curves and galvanostatic test. The microstructure of the alloys and the corroded surface of the specimens were investigated by scanning electron microscopy, X-ray diffractometry and emission spectrum analysis. It can be concluded that the addition of l%Ga （molar fraction） reduces corrosion current density from 26.98 mA/cm^2 to 2.34 mA/cm^2; while the addition of l%Hg （molar fraction） increases corrosion current density. The addition of Ga and Hg both promotes the electrochemical activity of the alloys and the influence of Ga is more effective than Hg. Mg-5%Hg-l%Ga alloy has the best electrochemical activity, showing mean potential of-1.992 V. The activation mechanism of the magnesium alloy produced by Hg and Ga was put forward. Magnesium atoms are dissolved in liquid Hg and Ga to form amalgam and undergo severe oxidation at the amalgam/electrolyte interface.     

新型无铅焊料合金Sn-Zn-Ga的研究

以Sn-Zn合金为母合金，添加Ga元素，得到了新型的无铅焊料合金。测量了其熔点、硬度、剪切强度和可焊性等性能。研究发现，Ga元素的添加使焊料的熔点降低，熔程增大。焊料的硬度和剪切强度有所降低。焊料的铺展率增大，浸润角减小，提高了焊料的可焊性。通过实验研究确定了具有较好综合性能的焊料的成分范围。     

The effect of alloying element gallium on the polarization characteristics of Pb-free Sn-Zn-Ag-Al-XGa solders in NaCl solution

The polarization characteristics of Sn-8.5Zn-0.5Ag-0.1Al-XGa lead-free solders were investigated in 3.5% NaCl solution where X ranges from 0.05-1.5 wt%. The results show that Ga affects the anodic polarization behaviour of the solders. Passivation behaviour is observed for all the investigated Sn-8.5Zn-0.5Ag-0.1Al-XGa solders. Increase in the Ga content from 0.05 to 0.25 wt% increases the ability for passivation but the oxide film formed due to passivity is not so protective. However Ga content > 0.25 wt% enhances corrosion and decreases the protective power of the passive film. The magnitude of the passivation current densities depend on the composition of the solders and the potentials applied. Layers of oxides of tin and zinc are responsible for the passivation behaviour. XRD and SEM results revealed the formation of corrosion products like SnO, ZnO, SnO₂ at different potentials during the polarization study.     

Effect of Ga content in Cu(Ga) on the growth of V3Ga following bronze technique

Diffusion–controlled growth rate of V₃Ga in the Cu(Ga)/V system changes dramatically because of a small change in Ga content in Cu(Ga). One atomic percent increase from 15 to 16 leads to more than double the product phase layer thickness and a decrease in activation energy from 255 to 142 kJ/mol. Kirkendall marker experiment indicates that V₃Ga grows because of diffusion of Ga. Role of different factors influencing the diffusion rate of Ga and high growth rate of V₃Ga are discussed.     

Effect of current density on micro‐arc oxidation of Q235 steel and corrosion resistance in liquid Pb‐Bi

An attempt has been made to improve the corrosion resistance in liquid Pb‐Bi by micro‐arc oxidation (MAO), and the effects under different current densities on the corrosion resistance of the coatings were discussed. Scanning electron microscope, energy dispersive spectrometer, and X‐ray diffraction were used to analyze the surface morphology and phase constituents of the MAO coatings produced under different current densities. The corrosion resistance of the coatings was evaluated by studying the element changes and morphology evolution. The results show that the compactness of the ceramic coating decreases with the current density increasing. In contrast to the performance of matrix metal, the ceramic coating exhibited a much better corrosion resistance in liquid Pb‐Bi. Moreover, the ceramic coating produced under current density of 10 A/dm ² shows the best corrosion resistance.