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Abstract

The further development of Co-based superalloys requires to optimise the gamma/gamma-prime icrostructure and to suppress the precipitation of topologically close-packed (TCP) phases. Both optimisation targets depend directly on the local chemical composition. In order to gain an understanding of the formation of L12 and TCP phases, we apply structure maps that relate the structural stability of a compound to its chemical composition. The alloying elements enter in terms of the number of valence electrons, the atomic volume and the electro-negativity. By combination with casting experiments and microstructure analysis, we demonstrate that a structure map for intermetallic phases correctly predicts TCP-phase precipitates from experimentally determined local chemical compositions in Co-based superalloys. From the stability window of the L12 phase in a structure map for sp-d valent compounds we determine modifications of the chemical composition of Co3(Al,W) that are likely to form a gamma/gamma-prime microstructure.