Eutectic growth in space

Defect-free eutectic components are favoured for certain applications in view of their improved performance and/or better stability. Eutectics produced even under best conditions possible on earth have some microstructural defects. Unavoidable density driven convectional currents in liquid are considered as a major cause for the production of these defects. Intensity of such convectional currents proportionally reduces with gravity. Therefore the defect density in the eutectics is expected to be very low when processed under microgravity conditions. The advantages and limitations of processing under microgravity conditions are examined. The potential of newly developed ‘skin technology’ for processing eutectic components in space is considered.     

Predictability of Eutectic Microstructures

The interphase spacings σ in the microstructures of most binary and pseudobinary “normal” metallic eutectics can roughly be quan- tified with regard to their respective solidification rates v according to a general relationship constant the constant being commonly between 10^?10 and 10^?11 cm^{3 ?1} The designation “normal” relates to similar degrees of undercooling of either phase on a plain-front solidification process at variance with anomaleous eutectics which solidify at different degrees of under- cooling in an uncoupled or weakly-coupled manner. The “constant”, however, is an individual value for each eutectic system. It is lowest for “simple” eutectics forming no intermetallic com- pounds and having low terminal solid solutions. The constant is raised for systems by 3 orders of magnitude or more if extensive terminal solid solutions are present. A closer fit for deliberate normal eutectics is presented in this pragmatic approach if the concentration differences between the terminal phases in eutectics ΔC_E [at%] are attributed to them as a square term according to λ² + · v · ΔC_E² = constant. The data based on this relation still show some scatter but they are grouping to distinct material families e. g. to Pb-, Ag- or Al-based eutectics. The remanent differences are estimated to disappear as soon as the relation is extended by the interdiffusion coefficient D according to as is confirmed in cases where reliable D values are available. These findings are in contrast to the current published theories on eutectic solidification. Suggestions are given where the bound- ary conditions have to be altered in order to attain full accord be- tween experiment and theory.     

Eutectic and peritectic solidification patterns

Recent advances in the understanding of eutectic and peritectic two-phase pattern formation under purely diffusive transport are reviewed. The parallel progress of two key techniques, namely, in situ experimentation with model, low-melting transparent and metallic alloys in thin and bulk samples, and numerical phase-field simulations, is highlighted. Experiments and simulations are interpreted in the light of the theory of non-equilibrium pattern formation phenomena. Focus is put on microstructure selection and morphological transitions, multiscale patterns in ternary alloys, and the influence of crystallographic effects on pattern formation. Open problems, for example on crystallographic effects, irregular eutectics, and peritectic solidification, are outlined.     

蒙特卡罗法模拟Pb-Sn共晶合金

用蒙特卡罗方法模拟Pb-Sn二元共晶合金在给定的试验条件下晶粒长大过程和凝固组织的形态,及其物理参数温度梯度G,生长速率V,冷却速率GV和晶体的层间距λE之间的关系,模拟的结果与以前试验结果吻合较好。     

定向凝固共晶多相复合陶瓷的研究现状

本文评述了定向凝固共晶多相复合陶瓷的制备方法, 并介绍了定向凝固 Ａｌ_２ Ｏ_３/ Ｙ Ａ Ｇ 共晶复合材料优异的高温强度、热稳定性以及抗蠕变性断裂强度达３５０ ～４００ Ｍ Ｐａ , 且从室温到２０７３ Ｋ 基本不变; 在１９２３ Ｋ 以上拉伸试验, 显示出由位错运动引发的塑性形变; 且观察到类似于金属的屈服现象这种复合材料经１９７３ Ｋ/１０００ｈ 空气中热处理后的显微结构也十分稳定有望成为２１ 世纪新的耐热结构材料     

Eutectic Solidification in Near-eutectic Al-Si Casting Alloys

Eutectic solidification in near-eutectic Al-13 wt pct Si casting alloys and the effect of trace addition of boron or strontium on it have been investigated using thermal analysis and microstructural characterization.In unmodified alloy,dual eutectic structure has been observed.The coarse eutectic(dendrite-like Al+ coarse Si flakes) is formed above the equilibrium temperature of eutectic(Al+Si) reaction(577℃).The coarse eutectic(CE) grains nucleate from the primary silicon particles formed earlier due to loc...     

金-硅共晶键合技术及其应用

采用金属过渡层来实现硅-硅低温键合,首先介绍了选择钛金作为金属过渡层的原因和金硅共晶键合的基本原理,然后探索了不同键合面积和不同金层厚度对金硅共晶键合质量的影响规律,开展了图形化的硅晶圆和硅盖板之间的低温共晶键合实验研究,获取了最优键合面积的阈值和最优金层厚度.最后将该低温金硅共晶键合技术应用到MEMS器件圆片级封装实验中,实验结果表明较好地实现了MEMS惯性器件的封装强度,但是还存在密封性差的缺陷,需进一步进行实验改进.     

Eutectic solidification in the NaF-MgF2 system

The compound NaMgF₃ occurs in the system NaF-MgF₂ and forms a eutectic with either component. The eutectic between NaF and NaMgF₃ has been unidirectionally solidified and the phase morphology and crystallography examined by optical and electron microscopy coupled with electron diffraction. Solidification with the complex-regular morphology from faceted cellular projections on the solid/liquid interface occurs for compositions on both sides of the eutectic point. Extensive regions of rod-like morphology occur in specimens where one of the macrofacet planes, constituting the faceted projections, is perpendicular to the direction of heat extraction.An analysis of twinning observed in the NaMgF₃ phase shows that it occurs in accommodation of lattice strain associated with a distortion of the unit cell axes on cooling from the growth temperature. These small distortions involve a progressive reduction in crystal symmetry from a cubic high temperature form to orthorhombic at ambient temperatures. The twins are not associated with the eutectic growth process in providing re-entrant edges to facilitate coupled growth of the two phases.     

固体雾化铝硅合金的粉末特性

固体雾化是一种新型的制粉方法 ,通过改变雾化介质来改善雾化效果。本文利用固体雾化方法制备了共晶铝硅合金 ,并与在相同条件下的普通气体雾化的同种粉末作了比较 ,发现采用固体雾化法制备的粉末细 ,粒度分布窄 ,冷却速度高     

基于共晶系相变材料的研究进展

基于相变材料的热能储存技术已被公认为是提高可再生能源利用效率和保护环境的先进能源技术之一.相变材料(PCMs)可以作为储能介质,在熔融或凝固过程中,PCMs可以在几乎恒定的温度下储存或释放大量的能量,被广泛应用于潜热储能系统和热管理系统中.相变温度是对相变材料进行选择的一个重要参数.通常具有特定要求相变温度的PCMs不存在,并且单一相变材料的相变温度和潜热比较固定,也难以同时满足对潜热、相变温度等的要求.因此,许多学者开展了二元或多元共晶相变体系的研究.文中介绍了近年来国内外共晶相变储能材料及其复合材料的研究进展及应用;探讨了共晶相变储能材料的相变理论推测及热力学建模;针对共晶体系在应用过程中存在的过冷、相分离、热导率低及相变时易泄露等问题,详述了解决这些问题的方法及进展,并提出了相关建议;最后对共晶系相变材料的热力学模型的建立与设计、热传导及循环稳定性等研究重点进行了展望.     

Sn40Pb共晶合金电镀工艺

目的对Sn40Pb共晶合金电镀工艺过程进行研究。方法采用电镀和超声辅助搅拌,Sn40Pb作为电镀阳极,在铜片上成功的制备了Sn40Pb共晶合金镀层。结果研究表明随着电流密度增大,镀层厚度增加,镀层中铅含量增加较快,电流密度过大时阴极析氢反应剧烈,锡铅镀层会变得粗糙,致密性变差。结论当电镀液成分为甲基磺酸为12 m L(24 g/L)、甲基磺酸锡为8 m L(16 g/L)、甲基磺酸铅为3.7 m L时,控制电流密度在4 A/dm~2、电镀时间为5 min左右,可以获得接近锡铅共晶的理想合金镀层。     

铁路冷藏车相变蓄冷材料的研制

通过研究添加剂对水合盐最低共熔点的影响，研制出一种-10～12℃相变蓄冷材料的组成为：10．5％NS、5％硝酸钾、0．01％苯骈三氮唑、0．1％硫酸铜、0．1％植酸和0．01％钼酸钠，其相变潜热为303．6kJ／kg，可以满足铁路冷藏车对相变蓄冷材料设计要求。     

快速凝固条件下的共晶生长理论

本文通过理论分析,导出了共晶生长条件下液相中溶质分布规律的一般表达式。理论结果表明,在快速生长条件下,λ~2V 不为常数,与生长速度 V、分配系数 K 和相体积比 f 等因素有关。Jackson—Hunt 模型中的λΔT、(ΔT~2)/V 关系在一般条件下应为λ(ΔT-ms)、(ΔT-ms)~2/V。在快速凝固条件下λ(ΔT-ms)和(ΔT-ms)~2/V 均不为常数,与 V、K、f 等因素有关。     

Heat Capacity of Nickel–Phosphorus Eutectic Melts

High Temperature - Ni–P alloys containing phosphorus from 15 to 23 at %, which is close to the eutectic concentration, are studied with differential scanning calorimetry. The heat capacity CP...     

The SnSe-SnSe2 Eutectic; aP-N multilayer structure

The conditions required to grow a two-phaseP-N heterojunction from a eutectic melt are discussed from general principles. It is shown that the lamellar SnSe-SnSe₂ eutectic exhibits 10³ to 10⁴ P-N heterojunctions per cm, and the crystallographic relationship between the SnSe- and the SnSe₂-lamellae is reported. A simple, chemical vapouretching technique is discussed which enables the components of the eutectic to be identified.     

氧化物共晶陶瓷定向凝固研究进展

定向凝固氧化物共晶自生复合陶瓷具有优异的高温强度、抗氧化性、抗蠕变性以及良好的高温结构稳定性,被认为是新一代在高温氧化性气氛中长期工作的首选超高温结构材料之一。回顾了氧化物共晶自生复合陶瓷的发展历史,总结了目前定向凝固氧化物共晶陶瓷凝固组织和力学性能方面的研究现状,同时结合作者在本领域的研究,着重分析了高温度梯度定向凝固条件下氧化铝基共晶陶瓷的组织特征、凝固特性、力学性能以及增韧机制。最后展望了定向凝固氧化物共晶陶瓷的发展趋势。     

铁路冷藏车共晶液的开发研究

通过研究不同无机盐对单一无机盐水溶液最低共熔点的影响,结果表明:添加无机盐可降低单一无机盐水溶液的最低共熔点;添加5%无机盐Kx的10.9%KNO3水溶液,其最低共熔点从-2.5℃下降到-5.4℃,相变潜热为307.16kJ/kg,可以满足铁路冷藏车共晶液的设计要求.