Effect of withdrawal rate on microstructure and lattice misfit of a Ni ₃Al based single crystal superalloy

A newly developed Re-containing Ni₃Al based single crystal superalloy was prepared by seeding technique. We investigated the effect of withdrawal rate (1-400 μm/s) on the microstructure and the γ/γ′ lattice misfit. With increasing withdrawal rate, the as-cast microstructure changed from planar to cellular and then to dendritic, accompanied by the significant refinement of dendrite arm and γ′ phases. The morphology of γ′ phases also transformed in response to different withdrawal rates, which was ascribed to the influence of the γ/γ′ lattice misfit. In association with the evolution of the microstructures, the liquid diffusion coefficients of Ni and Ni₃Al based superalloys were estimated by Kurz-Fisher model.