Planar Front Growth of Single Crystal Ni-Based Superalloy René N515

A Ni-based superalloy, René N515, was fabricated by the levitation zone melting process to produce planar front single crystal growth. Microstructure, alloy composition, and microhardness properties of the as-zone melted and solution heat treated alloy were investigated and compared with the directionally solidified state to study the effect of microsegregation on these alloy characteristics. In the planar front region, the dendritic structure and microsegregation were eliminated, and the density of casting porosity decreased as well. We modeled the zone melting/planar growth process by solving the zone melting mass balance equation numerically, and the measured and predicted composition profile of the planar front were in good agreement. The Vickers microhardness did not vary throughout the planar front region. These results indicate that a nearly homogeneous planar front of a 2nd-generation single Ni-based superalloy can be fabricated via levitation zone melting, and common casting defects can be eliminated entirely.