Clean metal nucleated casting of superalloys

Abstract

The clean metal nucleated casting program is a cooperative research program between GE Energy and Allvac, sponsored by the National Institute of Standards and Technology under the Advanced Technology Program. The goal of the program is to develop a spray-casting technology for the production of extremely large, segregation-free, superalloy ingots for use in turbine wheels in land-based gas turbines. The raw material for the process is a superalloy vacuum induction melted (VIM) electrode; in the CMNC process it is melted in a bottom-pouring Electro-Slag Remelting (ESR) furnace that forms a stream of liquid superalloy for subsequent atomization and collection in a withdrawal mold. Gas atomization of the stream to form a spray occurs in a chamber where spray distance and gas-to-metal flow rates can be adjusted to cool the metal to a desired level before collection. The approach taken in the R&D program is to address key technical risks associated with the system through construction of a one-ton research plant. These risks include the design and operability of the ESR furnace, pouring system, and collection system. Computational models of all key components of the process are developed and validated against experiments performed on the research plant. The validated models will be used to extrapolate to commercial-sized ingots.