Bi-2212超导线材的微观相调控及力学性能优化研究

Bi-2212（Bi2Sr2CaCu2Ox）superconductor has excellent high-field critical current characteristics, and is one of the ideal superconducting materials for high-field magnet applications. Further improving its critical current and improving mechanical properties are two major issues that need to be solved currently. The powder prepared by spray pyrolysis method can effectively improve critical current, but there is no report about corresponding mechanism research. In this project, Bi-2212 precursor powder will be prepared by spray pyrolysis method. Phase evolution of pre-decomposed powder and its influence mechanism on non-superconducting phase will be studied systematically to obtain a reasonable control method. What's more, high strength materials is cladded on Bi-2212 wire by the innovative 3D printing technology, and the outer surface is further protected by silver with electroplating method. Based on this strengthening method, the kinetics of oxygen diffusion and the kinetics of nucleation and recrystallization of superconducting phase will be studied. This work will possibility offer scientific basis for development of Bi-2212 wire with ideal superconducting and mechanical properties, which can satisfy the requirement of high-field magnet applications.

Bi-2212（Bi2Sr2CaCu2Ox）超导材料具有优异的高场临界电流特性，是面向高场磁体应用的理想超导材料之一。进一步提高其临界电流和改善力学性能是当前需要解决的两个主要问题。喷雾热分解方法制备的粉末可以有效提高线材临界电流，但相关机理研究尚属空白。本项目将基于喷雾热分解方法，系统研究预分解粉末的相演变规律及对非超导相的影响机制，获得合理的调控方法。另一方面，创新的采用3D打印技术在Bi-2212线材表面进行高强度材料镀化增强，外表面采用纯银进行电镀保护，并对该强化方式下线材热处理过程中的氧扩散动力学及超导相的形核再结晶动力学进行研究。本项目的开展将为探索满足未来高场磁体应用的具有理想超导性能和力学性能的Bi-2212超导线材提供科学依据。

Bi-2212超导材料具有优异的高场性能，是高场磁体应用和加速器磁体应用的理想材料。提高临界电流和改善力学性能是实现Bi-2212工程化需要解决的关键问题。本项目开发出了具有球状粉末颗粒、平均粒度小、均匀性好、反应活性高的Bi-2212粉末的喷雾热分解制备工艺。研究发现升高分解温度，可以加快粉末的分解和反应，但会形成不利于超导性能的Bi-2212相。对前驱粉末的成相热处理工艺研究发现，热处理气氛中的氧含量对粉末反应活性、相组分和晶粒结构有显著影响，增加氧含量可以提高线材的临界电流。将圆线进行轧制变形，可以提高芯丝致密度，减小热处理液相形成的孔洞，进而改善力学性能和临界电流密度。通过对线材引入预高压热处理，可以实现线材的减径，进而在后续高压热处理中全面消除芯丝孔洞。对线材的热处理发现，Bi-2212线材的热处理窗口很小，晶粒形核生长时间对提高线材临界电流密度具有显著的影响。基于本项目的研究，成功制备出500米长的Bi-2212线材，为后续工程化研究奠定了基础。