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111.
《科学通报(英文版)》2007,(19)
Rapid growth behavior of ■ phase has been investigated in the undercooling experiments of Cu-14%Ge, Cu-15%Ge, Cu-18.5%Ge and Cu-22%Ge alloys. Alloys of the four compositions obtain the maximum undercoolings of 202 K(0.17TL), 245 K(0.20TL), 223 K(0.20TL) and 176 K(0.17TL), respectively. As the content of Ge increases, the microstructural transition of "α (Cu) dendrite ■ peritectic phase →■ peritectic phase →■ dendrite (ε ■ ) eutectic" takes place in the alloy at small undercooling, while the microstructural transition of "fragmented α (Cu) dendrite ■ peritectic phase →■peritectic phase →■ dendrite ε phase" happens in the alloy at large undercooling. EDS analysis of the Ge content in ■ peritectic phase indicates that undercooling enlarges the solid solubility of α dendrite, which leads to a decrease in the Ge content in ■ phase as undercooling increases. In the Cu-18.5%Ge alloy composed of ■ peritectic phase, the Ge content in ■ phase increases when undercooling increases, which is due to the restraint of the Ge enrichment on the grain boundaries by high undercooling effect. 相似文献
112.
113.
基于轴对称电磁悬浮模型,理论计算了二元Fe_(50)Cu_(50)合金熔体内部的磁感应强度和感应电流,分析了其时均洛伦兹力分布特征,进一步耦合Navier-Stokes方程组计算求解了合金熔体内部流场分布规律.计算结果表明,电磁悬浮状态下合金内部流场呈现环形管状分布,并且电流强度、电流频率或合金过冷度的增加,均会导致熔体内部流动速率峰值减小,平均流动速率增大,并使流动速率大于100 mm·s~(-1)区域显著增大.通过与静态凝固实验对比发现,电磁悬浮条件下熔体中强制对流使得合金内部富Fe和富Cu区的相界面呈波浪状起伏形貌,并且富Cu相颗粒在熔体上部分出现的概率增加. 相似文献
114.
Under the conventional solidification condition, a liquid aluminium alloy can be hardly undercooled because of oxidation.
In this work, rapid solidification of an undercooled liquid Al80.4Cu13.6Si6 ternary eutectic alloy was realized by the glass fluxing method combined with recycled superheating. The relationship between
superheating and undercooling was investigated at a certain cooling rate of the alloy melt. The maximum undercooling is 147
K (0.18T
E). The undercooled ternary eutectic is composed of α(Al) solid solution, (Si) semiconductor and θ(CuAl2) intermetallic compound. In the (Al+Si+θ) ternary eutectic, (Si) faceted phase grows independently, while (Al) and θ non-faceted
phases grow cooperatively in the lamellar mode. When undercooling is small, only (Al) solid solution forms as the leading
phase. Once undercooling exceeds 73 K, (Si) phase nucleates firstly and grows as the primary phase. The alloy microstructure
consists of primary (Al) dendrite, (Al+θ) pseudobinary eutectic and (Al+Si+θ) ternary eutectic at small undercooling, while
at large undercooling primary (Si) block, (Al+θ) pseudobinary eutectic and (Al+Si+θ) ternary eutectic coexist. As undercooling
increases, the volume fraction of primary (Al) dendrite decreases and that of primary (Si) block increases.
Supported by the National Natural Science Foundation of China (Grant Nos. 50121101, 50395105) and the Doctorate Foundation
of Northwestern Polytechnical University (Grant No. CX200419) 相似文献
115.
Metastable phase separation and rapid solidification of undercooled Co-Cu alloy under different conditions 下载免费PDF全文
The metastable liquid phase separation and rapid solidification behaviours
of Co61.8Cu38.2 alloy were investigated by using differential
thermal analysis (DTA) in combination with glass fluxing, electromagnetic
levitation (EML) and drop tube techniques. It is found that the liquid
phase separation process and the solidification microstructures intensively
depend on the experimental processing parameters, such as undercooling
level, cooling rate, gravity level, liquid surface tension and the wetting
state of crucible. Large undercooling and surface tension difference of the
two liquids tend to facilitate further separation and cause severe
macrosegregation. On the other hand, rapid cooling and low gravity
effectively suppress the coalescence of the minority phase. Severe
macrosegregation patterns are formed in the bulk samples processed by both
DTA and EML. In contrast, disperse structures with fine spherical Cu-rich
spheres homogeneously distributed in the matrix of Co-rich phase have been
obtained in drop tube. 相似文献
116.
The solidification characteristics of three types of Pb-Sb-Sn ternary alloys with different primary phases were studied under
substantial undercooling conditions. The experimental results show that primary (Pb) and SbSn phases grow in the dendritic
mode, whereas primary (Sb) phase exhibits faceted growth in the form of polygonal blocks and long strips. (Pb) solid solution
phase displays strong affinity with SbSn intermetallic compound so that they produce various morphologies of pseudobinary
eutectics, but it can only grow in the divorced eutectic mode together with (Sb) phase. Although (Sb) solid solution phase
and SbSn intermetallic compound may grow cooperatively within ternary eutectic microstructures, they seldom form pseudobinary
eutectics independently. The (Pb)+(Sb)+SbSn ternary eutectic structure usually shows lamellar morphology, but appears as anomalous
eutectic when its volume fraction becomes small. EDS analyses reveal that all of the three primary (Pb), (Sb) and SbSn phases
exhibit conspicuous solute trapping effect during rapid solidification, which results in the remarkable extension of solute
solubility.
Supported by the National Natural Science Foundation of China (Grant Nos. 50121101 and 50395105) 相似文献
117.
研究了深过冷条件下三元Ni80Cu10Co10合金的快速枝晶生长, 采用电磁悬浮无容器处理方法获得了335 K(0.2TL)的最大过冷度. X射线衍射分析与差示扫描量热分析均表明,凝固组织为α-Ni单相固溶体. 随过冷度增大, 凝固组织显著细化, 并且当过冷度达110 K时,凝固组织的形态由粗大形枝晶转变为等轴晶. 深过冷条件下溶质截留效应增强, 使得微观偏析程度减小. 对不同过冷度下合金枝晶的生长速度进
关键词:
深过冷
枝晶生长
快速凝固
溶质截留 相似文献
118.
Results of thermal expansion prediction from atomic scale for metastable liquid metals are reported herein. Three pure liquid metals Ni, Fe, and Cu together with ternary Ni60Fe20Cu20 alloy are used as models. The pair distribution functions were employed to monitor the atomic structure. This indicates that the simulated systems are ordered in atomic short range and disordered in long range. The thermal expansion coefficient was computed as functions of temperature and atom cutoff radius, which tends to maintain a constant when the cutoff radius increases to approximately 15 Å. In such a case, slightly more than 1000 atoms are required for liquid Ni, Cu, Fe and Ni60Fe20Cu20 alloy, that is, the macroscopic thermal expansion can be predicted from the volume change of such a tiny cell. Furthermore, the expansion behaviors of the three types of atoms in liquid Ni60Fe20Cu20 alloy are revealed by the calculated partial expansion coefficient. This provides a fundamental method to predict the macroscopic thermal expansion from the atomic scale for liquid alloys, especially in the undercooled regime. 相似文献
119.
We discuss a 2D moving boundary problem for the Laplacian withRobin boundary conditions in an exterior domain. It arises asa model for Hele–Shaw flow of a bubble with kinetic undercoolingregularization and is also discussed in the context of modelsfor electrical streamer discharges. The corresponding evolutionequation is given by a degenerate, non-linear transport problemwith non-local lower-order dependence. We identify the localstructure of the set of travelling-wave solutions in the vicinityof trivial (circular) ones. We find that there is a unique non-trivialtravelling wave for each velocity near the trivial one. Therefore,the trivial solutions are unstable in a comoving frame. Thedegeneracy of our problem is reflected in a loss of regularityin the estimates for the linearization. Moreover, there is anupper bound for the regularity of its solutions. To prove ourresults, we use a quasi-linearization by differentiation, indexresults for degenerate ordinary differential operators on thecircle and perturbation arguments for unbounded Fredholm operators. 相似文献