[SY-F5] Symposium F-5

[SY-F5] Phase-field study of eutectic colony formation in NiAl-34Cr

^○Michael Kellner^1,2, Johannes Hötzer^1,2, Markus Linnenberg¹, Marco Seiz¹, Britta Nestler^1,2 (1.Institute of Applied Materials - Computational Materials Science (IAM-CMS), Karlsruhe Institute of Technology, Germany, 2.Institute of Digital Materials Science (IDM), Karlsruhe University of Applied Science, Germany)

The properties of a material are mainly defined by their chemical composition and by their underlying microstructure. Therefore, the development of tailored microstructures is crucial for the applicability in high-performance materials with specified properties. Depending on the material properties and process conditions, multi-scale microstructures evolve during the directional solidification of eutectics. Beside the microscopic eutectic lamellar and/or fibrous structures, macroscopic structures like eutectic colonies occur at certain process conditions. Eutectic colonies are mainly observed in ternary systems when the composition of the alloy is in the vicinity of a binary eutectic reaction. The formation of colonies is driven by microscopic instabilities in a macroscopic planar solidification front, due to the impurities by the third component that diffuse from the two solidifying phases into the liquid.

To simultaneously investigate the formation processes of micro- and macroscopic structures in their complex spatial arrangement, two- and three-dimensional large-scale phase-field simulations based on a Grand potential formalism are conducted for the high-performance material NiAl-34Cr. By systematic variations of the solidification velocity beyond the stability range the underlying mechanisms leading to the formation of eutectic colonies are studied. Further the interactions and the coherences between the eutectic rod-like structure of NiAl-34Cr and the arrangement of the eutectic colony are investigated. Especially the contact zones between the colonies are of interest, as these are indicated to be the weak points for the applicability. In additional studies the stability of the colonies for different temperature gradients and off-eutectic melt compositions is observed.