Phase-field study of dynamic velocity variations during directional solidification of eutectic NiAl-34Cr

Abstract

Ecological and economical demands require the development of materials with tailored microstructures and properties. The process conditions during the directional solidification of a eutectic alloy directly influence the scale and the type of the arising microstructure and hence the resulting macroscopic properties. Due to dynamic variations of the growth velocity, macroscopic components with locally differing microstructures can be achieved. The underlying rearrangement processes resulting in characteristic patterns are the focus of current research. To investigate the temporal evolution of these processes in three-dimensions, large-scale parallel phase-field simulations of the eutectic NiAl-34Cr alloy with systematically varied growth velocities are conducted. The microstructure evolution is quantitatively assessed by measurements of fiber spacings, shape factors, average front undercoolings and by microstructure adjustment events. Depending on the amount and type of the velocity variations, different microstructures such as a mixture of lamellae and fibers as well as hexagonal arranged rods evolve. The results demonstrate that the ordering rate of the fibers is directly correlated to the process history of the velocity variations.