Interfacial Segregation of Fe and Si on TiB2 Surface and Refinement of Fe-Bearing Intermetallic Compounds and Primary Si

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Abstract
Al–Ti–B-based grain refiners have been successfully used in the aluminium industry for more than six decades. Recent advancements have demonstrated that manipulating the nucleation potency of substrates through interfacial segregation can enhance the heterogeneous nucleation of both single-phase and intermetallic compounds by providing structural and compositional templating. However, the segregation of Fe and Si, two of the most common alloying elements or impurities in Al alloys, on TiB2 surface and its subsequent effects are not fully understood. In this work, TiB2 particles were synthesized in an Al–3.7Ti–1.5B alloy melt containing 0.43 wt pct excess free Ti, followed by isothermal treatment to promote Fe and Si segregation on the TiB2 surface. The segregation behaviour of Fe and Si on different terminated surfaces of the TiB2 particles was investigated using scanning transmission electron microscopy (STEM). The experimental results show that Fe and Si exhibit distinct segregation behaviours depending on the atomic configuration of TiB2 surfaces, leading to the formation of two-dimensional compounds (2DCs) at the Al/TiB2 interfaces. The formation of interfacial segregation layers has been shown to profoundly affect subsequent solidification, particularly nucleation and growth processes of intermetallic compounds (IMCs) in the alloys, resulting in significant refinement of these phases and the final solidification microstructure. In part 1, this research focuses on investigating the nature of interfacial segregation of Fe and Si on TiB2 particles. Experimental results concerning the segregation and the characterization of the structure and chemistry of the resulting interfacial layers are presented. In the subsequent Part II, the investigation will address the effects of Fe and Si interfacial segregation on the solidification behaviour of Al alloys, with particular emphasis on the heterogeneous nucleation and refinement of primary Fe-bearing intermetallic compounds and the primary Si phase in Al–Fe–Si and Al–Si alloys. Graphical Abstract

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