微波烧结铁素体合金中Ti(Si)-Y-O纳米团簇形成过程及强化机制

Nanocluster ferritic alloy (NFA) is attractive for the first wall due to the outstanding resistance to high temperature creep and irradiation. It is usually fabricated by mechanically alloying (MA) and subsquent hot isostatic pressing(HIP) or hot extrusion(HE), which will lead to expensive production. Meanwhile, the nanocluster in common NFA is simple, and these have limited the properties and the application of the alloy in a certain extent. In this research, Si was added into the material system and the microwave sintering was applied, which was to decrease the sintering temperature and form Ti(Si)-Y-O nanocluster in the alloy. The appropriate ratio of Si,Ti,Y and O atoms is analyzed and calculated by the theory of thermodynamic and first principles. On the basis of this, the dissolution mechanism of Ti, Si and Y2O3 into the matrix in the mechanical alloying and the precipitation and coarsing mechanism of nanocluster in the microwave sintering.with varing temperature are investigated and explained. Meanwhile, the dynamic equation refered to "dissolution-precipitation-coarsing" will be established. The essential relationship between the properties and the structure of the nanocluster is studied so as to control the fabrication and technologies with NFA materials. This work will provide crucial theoretic and practical advices for the improvement of the NFA technologies, and extend the application of the production of powder metallurgy and development of the first wall structure material in the nuclear industry.

纳米团簇铁素体合金（NFA）由于具有较好的抗高温蠕变及辐照性能，在核聚变堆第一壁结构材料上具有极大的应用潜力。该合金一般通过机械合金化+热等静压或热挤压工艺获得，工艺成本高且团簇结构单一，一定程度上限制了该材料的性能及应用。本项目拟向传统NFA材料体系中引入适量Si元素，并采用微波烧结工艺在较低的热固化温度下制备出含有Ti(Si)-Y-O复合纳米团簇的铁素体合金。通过热力学分析及第一性原理计算合理配置Si、Ti、Y、O原子比，在此基础上阐明Ti、Si、Y2O3颗粒在机械合金化中的溶解机理，以及纳米团簇在不同温度条件下微波烧结过程中析出与长大机制，并建立“溶解-析出-长大”的动力学模型，探索制备工艺与合金团簇结构及性能之间的内在联系，实现对NFA材料的工艺控制和技术掌握。这对于完善NFA材料技术体系，扩大粉末冶金应用领域及推动核能工业中结构材料的发展具有重要的理论和实践意义。

纳米团簇铁素体合金（NFA）因其良好的抗蠕变性与抗辐照性，被认为是核聚变堆第一壁结构的候选材料。本项目向传统Fe-Cr-W-Ti-Y2O3系NFA材料中引入Si元素，围绕Fe-Cr-W-Si-Y2O3与Fe-Cr-W-Ti-Si-Y2O3两种材料体系，基于第一性原理对Y、Ti、Si、O原子在bcc结构铁基体内的溶解特性、与空位间的相互作用及纳米团簇结合能等参数进行了计算，从理论上提出了合金成分的设计依据、机械合金化过程中各原子的溶解机理与高温烧结过程中纳米团簇的形成机制：在机械合金化过程中产生的大量空位优先与固溶于八面体间隙位置O原子结合形成稳定的O-空位对，随后会优先吸附Y原子，直到达到饱和，O-Y-空位对进而优先吸附Si原子，饱和O-Y-Si-空位对会吸附Ti，从而逐渐形成具有最低能量的O-Ti(Si)-Y纳米团簇；采用真空烧结与微波烧结制备了Fe-Cr-W-Si-Y2O3与Fe-Cr-W-Ti-Si-Y2O3合金，在合金基体中可观察到弥散分布的Y-Si-O及Y-Si(Ti)-O纳米结构；通过向合金体系中引入Si元素，成功实现了烧结温度的降低、第二相尺寸的减小以及合金性能的优化，1280℃真空烧结Fe-Cr-W-3Si-Y2O3合金的硬度为442.33HV，抗拉强度为1025MPa，该材料在1200℃微波烧结后具有更优的综合性能，其硬度为523.50HV，抗拉强度为1220MPa。Ti、Si同时添加有利于提高材料性能，1200℃微波烧结Fe-Cr-W-Ti-1Si-Y2O3合金的拉伸强度为894.2MPa，硬度为463.1HV。本项目制备出了性能良好的含Si NFA合金，阐述了纳米结构形成的内在规律，建立了工艺-组织-性能的联系，对NFA成功应用于核聚变堆第一壁结构材料提供了一定的理论依据与设计思路。