论文部分内容阅读
近年来原位法Cu—Nb_3Sn纤维复合超导材料的研究工作相当活跃。本文报导用电子探针研究在制备Nb_3Sn时热处理过程中元素分布的主要实验结果,并作了初步讨论。样品为由芯部Cu—95wt％Sn的合金外面依次包复无氧Cu、Cu—20wt％Nb合金,再无氧Cu组成的线材。经不同温度和时间热处理的样品横断面元素的含量变化如图1。从图中观察到在400℃以下热处理时,出现Sn、Cu浓度台阶,这种台阶来源于成分范围很窄的ε和η相。400℃热处理后,元素的扩散分布有几个明显的特征:Cu—Nb合金管内壁相对样品中心向外移动了约6μm;合金管内壁Nb含量增高了一倍,形成一个厚约10μm的富Nb区;Sn—Cu合金芯已全部形成ε相。Nb纤维的移动,与Silva等研究Kirkendall效应时所观察到的惰性标记向αCu(Sn)一方移动恰好相反。Nb纤维向纯Cu一方移动表明Cu原子进入Sn—Cu合金的扩散流大于Sn原子进入Cu中的扩散流。产生这个现象的原因是形成了ε相。在我们这里则服从于Dyson等提出的Cu在Sn中的间隙扩散模型。550℃热处理时,CU—Nb合金管内壁及富Nb区不再变化,这和芯部祗能形成一定数量的ε相有关。这从实际计算和实验测定的ε相扩展范围和富Nb区的边界基本一致得到证实。
In recent years, in situ Cu-Nb_3Sn fiber composite superconducting materials research work quite active. In this paper, the main experimental results of the elemental distribution during heat treatment in the preparation of Nb_3Sn by electron probe were reported and discussed. The sample is composed of an outer layer of Cu-95 wt% Sn alloy coated with an oxygen-free Cu, a Cu-20 wt% Nb alloy and an oxygen-free Cu composition. The changes of the content of the cross-section elements of the samples heat-treated at different temperatures and times are shown in FIG. 1. It is observed from the figure that when the heat treatment is performed below 400 ° C, Sn and Cu concentration steps appear, which step is derived from the ε and η phases with a narrow composition range. After heat treatment at 400 ℃, there are several obvious characteristics of element diffusion distribution: the inner wall of Cu-Nb alloy tube moves outwardly about 6μm from the center of the sample; the content of Nb in the inner wall of the alloy tube doubled to form a Nb Region; the Sn-Cu alloy core has all formed the ε phase. The movement of Nb fibers is exactly the opposite of the movement of the inert marker towards αCu (Sn) on the one observed by Silva et al. For the Kirkendall effect. Movement of the Nb fibers toward pure Cu shows that the diffusive flow of Cu atoms into the Sn-Cu alloy is greater than the diffusion flow of Sn atoms into the Cu. The reason for this phenomenon is the formation of ε phase. In our case, we follow the diffusion diffusion model of Cu in Sn proposed by Dyson et al. When heat treatment at 550 ℃, the inner wall of Cu-Nb alloy tube and Nb-rich region no longer change, which is related to the fact that only a certain amount of ε phase can be formed in the core. This is confirmed by the fact that the calculated and experimentally determined ε-phase extension range is basically in agreement with the boundary of the Nb-rich region.