Numerical prediction of primary dendrite arm spacing (PDAS), properties of the mushy zone, and freckle risk for various multicomponent Ni-base superalloys using the 3D-phase-field method

Thermo-physical data of the semi-solid region in directionally solidified materials are difficult to obtain by experiments, but at the same time of high importance for the prediction of casting defects like freckles, hot-tears, or micro-porosity, and further provide input for mesoscopic or macroscopic models. This paper shows how data like phase fractions, compositions, enthalpies, densities, as well as the melt permeability can be obtained for the whole range between liquidus and solidus temperature, and how an integral alloy-specific freckle risk can be assessed by performing 3D-phase-field simulations of a representative volume of the mushy zone. A phase-field model has been set up, and simulations have been done for the multicomponent Ni-base superalloys CMSX-4, SC2000, MAR-M247, and an MTU-test alloy using the software MICRESS® with online-coupling to thermodynamic and mobility databases. Furthermore, a numerical prediction of the primary dendrite arm spacing (PDAS) is provided by systematic variation of the simulation domain size using different methods based on the dendrite tip temperature and the diffusion fields in the liquid phase. The results are discussed against analytical relations.