WEB Thermodynamics and kinetics of core-shell Al3(Sc,Zr) precipitate formation in Al-based alloysWednesday (23.09.2020) 16:25 - 16:40 M: Modelling and Simulation 2 Part of:
One promising route to improve the mechanical behaviour of Al-based alloys is to enhance the coarsening resistance of second phase particles. A typical example is the addition of Zr to Al-Sc alloys where the Al3Sc particles are stabilized due to the Zr segregation at particle interfaces.
Our experiments subjected to varying processing conditions including extrusion, annealing and severe plastic deformation result in a rich microstructure characterized by two distinct categories of second phase Al3(Sc,Zr) particles: one with almost uniform distribution of Sc and Zr and the other with a Sc-rich core and Zr-rich shell. Furthermore, the chemically heterogeneous core-shell structures are found to exhibit an anisotropy in the Zr distribution along different crystallographic orientations of the precipitate-matrix interfaces.
Using density functional theory based calculations, we disentangle the sensitive interplay between the bulk and interfacial thermodynamics explaining the observed microstructure. The computed mixing enthalpy trends obtained from cluster expansion predict the homogeneous distribution of Sc and Zr on the Sc-sublattice as the thermodynamically stable configuration, while the core-shell structures are purely of kinetic origin. Therefore, the relevance of interfacial segregation in determining the growth of core-shell structures is evaluated. While the interface energy of the (100) Al/Al3(Sc,Zr) coherent interfaces is lowest, Zr segregation energy in front of the growing (110) and (111) Al3(Sc) facets is found to be the largest, explaining the chemical anisotropy of the core-shell structures.