GOALI: Microalloying and Improvement of the Solidification Characteristics of Nickel-Base Single Crystals

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This project is aimed at greater understanding of the mechanisms responsible for the breakdown of single crystal solidification and their dependence on alloy chemistry of nickel-base superalloy single crystals that find technological applications in improving performance and efficiency of aircraft engines. Carbon additions represent a promising new approach to improving the solidification characteristics of a broad range of alloys. However, the underlying mechanisms are not well understood. Careful control of carbon and other microalloying constituents could have a substantial impact on the production of large single crystal components. The main goals of the project are to determine the influence of microalloying additions, including boron, zirconium, nitrogen, hafnium and magnesium that affect the carbide precipitation process, the liquidus temperature and partitioning of major elements during solidification. The project examines the influence of these additions on freckling, segregation during solidification and precipitation processes near the liquidus. Directional solidification experiments are conducted in a Bridgman apparatus with conventional radiation cooling and with the use of liquid metal tin as a coolant. The role of alloying is examined with the use of segregation mapping techniques, differential thermal analysis and electrochemical extractions of precipitates. The work is performed in close collaboration between University of Michigan and General Electric Company (Corporate Research and Development, GE-CRD and General Electric Power Systems, GE-PS). GE-CRD will provide support for an extended sabbatical visit of the co-P.I. to the University of Michigan, to facilitate the interaction with student(s) supported on the program. Additionally, student(s) will jointly design experiments with GE-PS personnel as well as visit their engineering and manufacturing facilities.This research develops new understanding of the mechanisms involved with solidification of nickel-base superalloy single crystals for improved performance and efficiency of aircraft engines. The research will lend significant opportunity for academic personnel and students to interact with industrial counterparts.