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

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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.