Computational Simulations using Time-Dependent Ginzburg–Landau Theory for Nb–Ti-like Microstructures—Critical current data

Simulations based on time-dependent Ginzburg–Landau theory are employed to determine the critical current for a model system which represents a Nb–Ti-like pinning landscape at low drawing strain. The system consists of ellipsoids of normal metal, with dimensions 60ξ × 3ξ × 3ξ, randomly distributed throughout the superconducting bulk with their long axes parallel to the applied current and perpendicular to the field. These preciptates represent the α-Ti elongated precipitates which act as strong pinning centres in Nb–Ti alloys. We present the critical current density as a function of field across the entire range of precipitate volume fractions and find that optimised material in our model system occurs at 32 vol.% ppt., whereas in real materials the optimum occurs at 25 vol.% ppt.本研究采用基于含时金兹堡-朗道理论（time-dependent Ginzburg–Landau theory）的数值模拟方法，针对低拉拔应变下具有类铌钛钉扎分布的模型体系，求解其临界电流（critical current）。该模型体系由尺寸为60ξ × 3ξ × 3ξ的正常金属椭球构成，这些椭球随机分布于超导块体内部，且其长轴均平行于外加电流、垂直于外磁场。上述正常金属椭球即为对应铌钛合金中作为强钉扎中心的α-钛长条状析出相。我们系统表征了临界电流密度（critical current density）随外磁场的变化规律，覆盖了全部析出相体积分数区间；研究发现，本模型体系中性能最优的材料组分对应32%体积分数的析出相（vol.% ppt.），而实际铌钛合金中的最优析出相体积分数则为25%。