![]() Unlike GBM during recrystallisation or grain growth, SGBM decouples SGBs from solidification microsegregation of solutes and/or impurities. In general, SGBM is less often observed in commercial cast alloys that contain a noticeable presence of second-phase particles, due to the particle pinning effect (note that GB particles can migrate along with moving GBs, known as ‘mobile particles’ 28, especially at elevated temperatures, depending on their properties, sizes, and interactions with GBs). More SGBM phenomena were subsequently observed in as-cast, welded, wire-deposited (AM-fabricated) metals or alloys. Chernyshova reported SGBM in both as-cast niobium-tantalum alloys and weld seams of niobium metal in 1967 according to ref. 1b, referred to as SGB migration (SGBM).īiloni 8 first pointed out the prospect of SGBM in 1961 to elucidate the grain structures observed in as-cast pure aluminium (Al, 99.99 wt.%). However, exceptions do occur, where SGBs can migrate to decouple themselves from their initial as-solidified boundaries, as shown schematically in Fig. 1a 1, SGBs normally coincide with the peripheries of the coalescing crystals of different orientations. In this last stage, the liquid film composition and thickness remain little changed until the required coalescence or bridging undercooling is reached for the liquid film to solidify as a SGB 3, 4, 5, 6, 7. It results from the solidification of the last liquid film (~1 nm thick) between two grains with solute composition \(\) denotes the solid fraction. The basic principles for the formation of such an interface or solidification grain boundary (SGB) in the last-stage solidification have been delineated by Rappaz 3, 4 and other researchers 5, 6, 7. During solidification, an interface will form between two coalescing crystals of different orientations. Solidification is an essential manufacturing process or step for various metal products, including metal additive manufacturing (AM). They are an integral part of polycrystalline materials and exert a profound influence on almost all of their useful properties 2. Grain boundaries (GBs) are interfaces where crystals of different orientations meet 1. hot or liquation cracking during reheating, intergranular corrosion or fracture). The findings of this study extend perspectives on solidification grain structure formation and control for improved performance (e.g. SGMB does not depend on cooling rate or time but relates to grain size. A theoretical model is then developed for SGBM in dilute binary alloys, focusing on the effect of solute type and content, and applied to 10 alloy systems with remarkable agreement. Here, we first show the salient features of SGBM in magnesium-tin alloys solidified with cooling rates of 8−1690 ☌/s. They can migrate, but unlike normal GB migration, SGB migration (SGBM) decouples SGBs from solidification microsegregation, further affecting material properties. Solidification grain boundaries (SGBs) result from the solidification of the last liquid film between two abutting grains of different orientations. Solidification processing is essential to the manufacture of various metal products, including additive manufacturing.
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