Hierarchical microstructure and properties of ferritic alloys strengthened by two-phase intermetallic precipitates

本研究的重点是开发通过两相L21-Ni2TiAl / B2-NiAl金属间相强化的铁素体合金及其显微组织演变的表征。两种含铁素体元素Fe、Al、Ni和不同Ti含量的铁素体合金在固溶和时效热处理过程中的组织特征。采用先进的透射电子显微镜技术，如HAADF-STEM、ALCHEMI和原位电子显微镜来确定相分解途径、相应基体和析出相的晶体结构以及析出相-位错的相互作用。研究的重点是从原子层面到微观层面发展导致L21-Ni2TiAl / B2-NiAl两相析出的形成机制。实验观察得到第一性原理计算的补充，并结合热力学方法研究界面性质。通过对金属间化合物的位置偏好和电子结构计算，获得了对相稳定性的进一步了解。

The proposed research focuses on the development of ferritic alloys strengthened through two-phase L21-Ni2TiAl / B2-NiAl intermetallic precipitates and the characterization of their microstructural evolution. The microstructure of two ferritic alloys with base elements Fe, Al, Ni and different Ti levels is characterized in the course of solution and aging heat treatment. Advanced transmission electron microscopy techniques such as HAADF-STEM, ALCHEMI and in-situ electron microscopy are used to determine phase decomposition pathways, the crystallographic configuration of the corresponding matrix and precipitate phases and precipitate-dislocation interactions. The main focus is to develop formation mechanisms from the atomic to the microscopic level that lead to the formation of two-phase L21-Ni2TiAl / B2-NiAl precipitates. The experimental observations are complemented by first-principles calculations, which are coupled with thermodynamic approaches to study interfacial properties. Additional insight on the phase stability is obtained by site-preference and electronic structure calculations of the intermetallic compounds.