Simulation of Solidification Structures of Faceted 123 Peritectic Crystals in Superconductive YBCO Oxide
Simulation of Solidification Structures of Faceted 123 Peritectic Crystals in Superconductive YBCO Oxide
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超导 YBCO 氧化物中刻面 123 包晶晶体的凝固结构模拟
DOI：
10.2320/matertrans.42.220
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发表时间：
2001
影响因子：
1.2
通讯作者：
K. Ōgi
中科院分区：
文献类型：
--
作者：
N. Mori;K. Ōgi
由于微观/宏观结构会影响超导YBCO氧化物的临界电流密度（Jc）和力学性能，因此对液相+211 （Y2BaCuO5）相中多面123 （YBa2Cu3O7−X）晶体的凝固过程进行数值和分析研究对于阐明凝固机理和改善YBCO的性能至关重要。为了阐明生长方式和条件对123晶体微观结构的影响，通过考虑(a) 123晶体的生长，(b) 211颗粒在液体中的熔化，(c)溶质在液体中的扩散，对123晶体的面形包晶生长进行了二维数值模拟。123晶体的生长速率R近似为：R=ag·ΔTk2，其中ag为动力学生长常数，ΔTk为多面界面的动力学过冷。采用动力学熔融常数（am）和过热度（ΔTm）对211相的熔化速率进行了评价。利用FDM计算了123生长过程中液体中的溶质分布，并根据实验得到的YBCO液体中211颗粒的对数正态分布，评价了多面体123晶体中残余211颗粒和液池的分布。计算结果与实验结果吻合较好。实验和分析还研究了单向凝固YBCO中柱状到等轴123晶体的宏观组织转变。根据成核和生长理论计算了临界转变条件（生长速率R与温度梯度G的关系），并与实验结果进行了比较。
Since the micro/macro-structures affect the critical current density (Jc) and the mechanical properties of superconductive YBCO oxides, the following 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 . To clarify the effects of growth mode and conditions on the microstructures of 123 crystals, two-dimensional numerical simulation of faceted peritectic growth of 123 crystal was performed by considering (a) growth of 123 crystal, (b) melting of 211 particles in the liquid, and (c) solute diffusion in the liquid. The growth rate (R) of 123 crystal was approximated by: R=ag·ΔTk2, where ag was kinetic growth constant, and ΔTk was kinetic undercooling of faceted interface. The kinetic melting constant (am) and superheating (ΔTm) was also used for evaluation of melting rate of 211 phase. Solute distributions in the liquid during the 123 growth were calculated by FDM, and the distributions of residual 211 particles and liquid pools in the faceted 123 crystals were evaluated from the experimentally obtained log-normal distributions of 211 particles in the liquid of YBCO . The calculated results agreed well with the experimental ones. Transition of macrostructures from columnar to equiaxed 123 crystals in unidirectionally solidified YBCO was also studied experimentally and analytically. Critical transition conditions (:relations of growth rate (R) and temperature gradient (G)) were calculated by equations obtained from nucleation and growth theories, and compared with experimental results.