Prunitsa V. Nanocrystallization in amorphous alloys based on aluminum and iron.

The dissertation research focuses on studying the structure and phase transformations of amorphous metallic alloys based on the Al-Ni-Si, Fe-Si-B, and Co-Ni-Fe-Si-B systems. Amorphous alloys are distinguished by their unique physicochemical properties, such as high resistance to corrosion and radiation, as well as improved magnetic and mechanical characteristics. These properties enable the extensive application of amorphous materials in various industries, including mechanical engineering, energy, aviation, and electronics. Nanocrystallization, which occurs in the amorphous matrix under thermal treatment, is of particular interest as it allows significant changes in the material's structure and improves its performance characteristics. During thermal treatment, nanocrystalline phases are formed, which possess stable structures under specific thermodynamic conditions, enhancing many properties, particularly magnetic and mechanical ones. This study established that the structural evolution of amorphous alloys Al65Ni10Si25 and Al70Ni10Si20 follows a three-stage process and demonstrated that changes in the chemical element concentrations in these alloys result in shifts in the crystallization onset temperature. The stability of the hexagonal phase in aluminum-enriched amorphous alloys of the Al-Ni-Si system was investigated, allowing the hypothesis that the decomposition of the metastable H-phase in aluminum-based alloys depends on temperature but is independent of annealing duration. The method of electro-contact heating was used to study the structural modification of the amorphous alloy Fe73,5Nb3Cu1Si15,5B7. It was shown that heating through Joule heat generated during the passage of electric current leads to structural transformations and crystallization of the amorphous phase, which depend on the applied voltage. The magnetic properties, thermodynamic stability, and crystallization mechanism of the amorphous alloy Co57Ni10Fe5Si11B17 were also studied. It was found that this alloy is stable at temperatures below 760 K, while structural transformations occur at higher temperatures, leading to the crystallization of the alloy. Additionally, it was shown that the crystallization of the Co57Ni10Fe5Si11B17 alloy follows a two-stage process. No formation of ternary intermetallics was observed in the studied amorphous alloys based on aluminum, iron, and cobalt, consistent with equilibrium phase diagrams.