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31.
Wanghui Yu 《偏微分方程(英文版)》1996,9(1):55-70
A quasisteady Stefan problem with curvature correction and kinetic undercooling is considered. It is a problem with phase transition, in which not only the Stefan condition, but also the curvature correction and kinetic undercooling effect hold on the free boundary, and in phase regions elliptic equations are satisfied by the unknown temperature at each time. The existence and uniqueness of a local classical solution of this problem are obtained. 相似文献
32.
The rapid solidification of Al-30%Cu-18%Ag ternary alloy is investigated by using the free fall method. Its solidified microstructure
is composed of θ(Al2Cu), α(Al) and ξ(Ag2Al) phases. The liquidus temperature and solidus temperature are determined as 778 and 827 K, respectively. The alloy melt
undercooled amounts up to ΔT
Max=171 K (0.20T
L). Its microstructural evolution is investigated based on the theoretical analysis of undercooling behavior and nucleation
mechanics. It is found that the undercooling increases with the decrease of the diameter of the alloy droplet. When ΔT<78 K, the primary θ(Al2Cu) phase of the alloy grows into coarse dendrite. When 78 K⩽ΔT⩽171 K, its refined θ(Al2Cu) phase grows alternatively with α(Al) phase. Once ΔT⩾171 K, its microstructure is characterized by the anomalous (θ+α+ξ) ternary eutectic.
Supported by the National Natural Science Foundation of China (Grant Nos. 50121101 and 50395105) 相似文献
33.
<正>This paper investigates the solidification behaviour of the Ag—Cu eutectic alloy melt undercooled up to 100 K.It is revealed that lamellar eutectics grow in a dendritic form in the Ag-Cu eutectic melt with undercooling equal to or greater than 76 K.As undercooling increases,the remelted fraction of the primary eutectics during recalescence rises. The severe remelting and the subsequent ripening of the primary eutectic dendrites lead to the formation of anomalous eutectics. 相似文献
34.
Electromagnetic levitation technique was used to undercool bulk samples of Co-20% Cu and Co-60% Cu alloys and high undercoolings up to 303 and 110 K were achieved,respectively.The dendritic growth velocities were measured as a function of undercooling.The dendrite growth velocity of the Co-20% Cu alloy was much higher than that of the Co-60% Cu alloy.The experimental data were analyzed on the basis of the LKT/BCT dendritic growth model by taking into account non-equilibrium interface kinetics.It has been re... 相似文献
35.
Pedersen A. S. Pryds N. Linderoth S. Larsen P. H. Kjøller J. 《Journal of Thermal Analysis and Calorimetry》2001,64(3):887-894
Differential Scanning Calorimetric measurements were performed for accurate determination of the solidus and liquidus temperature
of Sn–Pb alloys. The difference between onset and end temperature of the melting peak depended clearly on alloy composition.
The results obtained were found to be in good agreement with the existing equilibrium phase diagram for the Sn–Pb system,
although the data suggested a slight correction of the eutectic composition. Under cooling conditions a large variation in
the onset temperature for solidification was found. A large number of heating and cooling cycles were performed in order to
investigate the statistical variation of the solid nucleation process.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
36.
在落管无容器条件下实现了Cu-10%Pb亚偏晶和Cu_374%Pb偏晶的快速生长. 发现随着液滴 过冷度的增大, 亚偏晶中初生(Cu)相的生长形态经历“粗大枝晶→碎断枝晶→等轴晶”的转 变. 偏晶的组织形态从多个偏晶胞组织演化为单个偏晶胞组织. 理论计算表明,直径在1000 —60 μm之间的亚偏晶和偏晶合金液滴, 最大过冷度分别为269 K (02 TLL )和245 K (02 TMM). 亚偏晶合金中初生(Cu)枝晶的最大生长速度为24 m/s ,
关键词:
无容器处理
深过冷
晶体生长
相分离 相似文献
37.
A Ni-P solid solution phase was obtained by quenching of melts under a pressure of 4.5 GPa. This was considered as a metastable high pressure phase. Despite the lack of thermodynamic parameters for Ni80, P20 alloy under pressure, the degree of undercooling, nucleation frequency and crystal growth velocity were calculated. We conclude that metastable phases with the same composition as the melting phase, such as supersaturated solid solution phase and amorphous phase, are easily prepared by high-pressure quenching. 相似文献
38.
The undercooling of Ni–Fe alloy coating melt was in situ investigated by differential scanning calorimeter with flux processing technique. The highest undercooling of Ni–Fe alloy with 426 K was obtained as the thermal treatment temperature of the melt being 1904 K and the cooling rate being 50 K min?1. When cooling rate is fixed, the undercooling depends on the melt processing temperature, and increases rapidly at the first stage. The effects of thermal treatment temperature and cooling rates on the undercooling were discussed. 相似文献
39.
The phase separation and dendrite growth characteristics of ternary Fe-43.9%Sn- 10%Ge and Cu-35.5%Pb-5%Ge monotectic alloys were studied systematically by the glass fluxing method under substantial undercooling conditions. The maximum undercoolings obtained in this work are 245 and 257 K, respectively, for these two alloys. All of the solidified samples exhibit serious macrosegregation, indicating that the homogenous alloy melt is separated into two liquid phases prior to rapid solidification. The solidification structures consist of four phases including α-Fe, (Sn), FeSn and FeSn2 in Fe-43.9%Sn-10%Ge ternary alloy, whereas only (Cu) and (Pb) solid solution phases in Cu-35.5%Pb-5%Ge alloy under different undercoolings. In the process of rapid monotectic solidification, α-Fe and (Cu) phases grow in a dendritic mode, and the transition "dendrite→monotectic cell" happens when alloy undercoolings become sufficiently large. The dendrite growth velocities of α-Fe and (Cu) phases are found to increase with undercooling according to an exponential relation. 相似文献
40.
Through phase transformation kinetic analysis and experimental observation, the δ/γ transformation occurring in the non-equilibrium peritectic Fe-4.33at.%Ni alloys was systematically investigated. According to JMA solid-state transformation kinetic theory, the Time-Temperature-Transformation (TTT) curves of the δ/γ transformation in peritectic Fe-Ni alloy were calculated. On this basis, the physical correlation between the δ/γ transformation and the initial undercooling of melt (△T) was elucidated. The results indicate that the change of △T can alter not only the overall δ/γ transformation pathways but also the transformation fraction with respect to each transformation mechanism. 相似文献