Abstract
A new nickle-base single crystal superslloy was developed by applying an "alloy designing" method, which was originated by Watanabe and improved by a group of the National Research Institute of Metals (NRIM). The typical composition range was 6-7 %Cr, 5-6 %Al, 5-8 %W, 5-8 %Ta and 4-6 %Mo (mass%). This alloy had more stable microstructure and higher creep rupture strength than single crystal superalloys so far developed. The basic flow of the designing was as follows. First, the composition of γ and γ' phases and the volume fraction of γ'phase were determined according to the NRIM scheme varying the combination of molar percentages of tungsten, tantalum and molybdenum included in γ' phase. Second, the most desirable combination of γ and γ' couples were selected to maximize the summed values of γ and γ' lattice constants and minimize the misfit between γ and γ' phases. Third, the stability of γ phase during solution heat treatment was assesed by introducing a new parameter of "Solubility Limit Index", whose value was defined by the solubility of included elements into nickel matrix.
