Analysis and Simulation of Growth Process of Faceted 123 Crystals in Superconductive Oxide
Analysis and Simulation of Growth Process of Faceted 123 Crystals in Superconductive Oxide
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超导氧化物中123面晶体生长过程的分析与模拟
DOI：
10.2320/jinstmet1952.66.6_634
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发表时间：
2002
影响因子：
--
通讯作者：
K. Ōgi
中科院分区：
文献类型：
--
作者：
N. Mori;K. Ōgi
通过数值模拟和解析方法研究由+211（Y2 BaCuO 5）液相转变为小面123（YBa 2Cu 3 O 7-X）晶体的凝固过程，对于阐明YBCO的凝固机制和提高YBCO的性能具有重要意义。考虑123晶体的生长、211粒子在液相中的熔化和溶质在液相中的扩散，对123晶体的小面周晶生长进行了二维数值模拟。123晶体的生长速率（Vk）近似为：Vk=ak·（DTk/Tp），其中ak为动力学生长系数，ak= ak 0·[（tan j/B）· tan h（B/tan j）·{1/cos（p/4）1}+1]，ak 0为生长常数，B为常数，j为界面与晶面的夹角，DTk为晶面界面的动力学过冷度，Tp为过晶温度。用有限差分法计算了123晶体生长过程中液相中的溶质分布，并由实验得到的YBCO熔体中211粒子的对数正态分布模拟了小面123晶体中残留211粒子和液池的分布。计算结果与实验结果吻合较好。此外，还对定向凝固YBCO中123晶体从柱状到等轴的宏观组织转变进行了实验和分析研究。根据成核和生长理论得到的方程计算了临界转变条件（生长速率R和温度梯度G的函数），并与实验结果进行了比较。
The numerical and analytical studies of solidification process of faceted 123(YBa2Cu3O7-X) crystals from liquid +211 (Y2BaCuO5) phases are essential to clarify the solidification mechanism and improve the properties of YBCO. Twodimensional numerical simulations of faceted peritectic growth of 123 crystal were performed by considering growth of 123 crystal, melting of 211 particles in the liquid, and solute diffusion in the liquid. The growth rate (Vk) of 123 crystal was approximated by: Vk=ak・ (DTk/Tp), where ak: kinetic growth coefficient, ak=ak0・[(tan j/b)・ tan h (b/tan j)・{1/cos (p/4)1}+1], ak0: growth constant, b: constant, j: angle between the interface and facet plane, and DTk: kinetic undercooling of faceted interface, Tp: peritectic temperature. Solute distributions in the liquid during the 123 growth were calculated with FDM, and the distributions of residual 211 particles and liquid pools in the faceted 123 crystals were simulated from the experimentally obtained lognormal distribution of 211 particles in the YBCO melt. The calculated results agreed well with the experimental ones. Further, the transition of macrostructures from columnar to equiaxed 123 crystals in unidirectionally solidified YBCO was also studied experimentally and analytically. The critical transition condition (:a function of growth rate (R) and temperature gradient(G)) were calculated by equations obtained from nucleation and growth theories, and compared with experimental results.