Morphological characteristics of triple junction region and process of the peritectic reaction during directional solidification of Cu–Ge alloys

A huge triple phase region of the nonfaceted–nonfaceted peritectic reaction within a large temperature region (around 8 K) was obtained in directionally solidified Cu–Ge alloys, which provides a convincing experimental evidence for studying the morphology of peritectic reaction trijunction region. The huge non-isothermal triple phase region suggests that the peritectic reaction occurs in a composition range, which is different from the classic isothermal model with a fixed composition (Liquid + solid solution α(CuGe12) → solid solution ζ(CuGe12.8)). The geometrical morphology of triple junction region shows that the primary α phase remelted ahead of the growing peritectic phase and resolidified near the triple phase junction. And some new characteristics of the peritectic reaction were also observed and systematically analyzed. The results demonstrate that the peritectic reaction during directional solidification occurs in the style: Liquid + remelted α(CuGe(12∼12−x)) → ζ(CuGe(12.8–12.8+y)) + resolidified α(CuGe12). The x and y depend on growth conditions and alloy composition. The remelting and resolidification phenomenon were discussed in detail, in which the effects of temperature gradient, mechanical equilibrium and solute diffusion were considered. Orientation relationship between the phases was studied by the electron back-scatter diffraction (EBSD) technology.

► A huge triple-phase region (HTR) of the peritectic reaction (PR) was obtained.
► The morphology of the HTR shows that the primary phase remelted and resolidified.
► The HTR suggests that the PR occurs in a composition range.
► The mechanism of the remelting and resolidification of primary phase was given.
► The structure of the triple phase region was studied by EBSD.