高性能Nb3Al超导合金低温烧结成相机制及其微观组织调控

Nb3Al合金以其优异的超导性能在大型高场磁体领域具有广阔的应用前景。但由于符合化学计量比超导相成相困难以及加工成形工艺复杂等因素，至今Nb3Al超导线材的研究仍停留在实验室阶段。近几年发展起来的机械合金化+低温烧结工艺简单易操作、成品率高且热处理温度低，有望率先实现低成本Nb3Al超导线材的大规模制备。不过目前该方法形成的超导相仍偏离化学计量比且临界电流密度较低，难以满足实用要求。鉴于此，本项目拟综合采用原位实验监测和计算模拟来澄清Nb(Al)ss过饱和固溶体球磨形成机制及其在低温烧结过程中向超导相转变的动力学机制，并进一步探明低温烧结微观组织形成和演变规律及其与临界电流密度之间的内在关系。以此为指导，优化该制备工艺，开发并引入第三组元添加技术和线材冷压/热压施加技术，实现化学计量比Nb3Al超导相低温可控成相和相应微观组织的有效调控，全面提高合金的超导性能，推动高性能线材规模化制备。

The Nb3Al superconducting alloy has a broad application prospect in the huge high field magnets due to its excellent superconducting properties. However, all the research on the Nb3Al superconducting wires is still in the laboratory now because of its difficult synthesis of superconducting phase with stoichiometric ratio and complicate forming technology. The technique that mechanical alloying and subsequent low-temperature sintering developed these years is expected to firstly achieve large-scale preparation of low cost Nb3Al wires owing to its easy-to-handle, high-yield and low heat treatment temperature. But so far the composition of superconducting phase synthesized with this method still deviates from the stoichiometry and also its critical current density is too low to meet the requirements of practical application. Based on these backgrounds, combined with in-situ experimental measurement and computing simulation, this project will clarify the formation mechanism of Nb(Al)ss supersaturated solid solution during mechanical alloying process and the kinetics mechanism of phase transition from this Nb(Al)ss to Nb3Al during low temperature sintering process. Then the formation and evolution of low-temperature sintered microstructure in Nb3Al will be investigated. Furthermore, the internal relationship between microstructure and critical current density for Nb3Al will be also revealed. Accordingly, the technique that mechanical alloying and subsequent low-temperature sintering can be improved and optimized, and also the technologies of the third component doping and cold/hot pressing will be explored as its beneficial supplement. Finally, the controlled formation of Nb3Al superconducting phase with stoichiometric ratio as well as the design and regulation of corresponding microstructure will be achieved at low sintering temperature. As a result, the superconducting properties of Nb3Al alloy can be comprehensively improved and its high-performance wires will be prepared in large scale.