Discrete dislocation simulations of precipitation hardening in inverse superalloys

The low-temperature yield stress of a gamma' (Ni3Al) matrix-gamma (Ni) precipitate 'inverse' superalloy, containing 40% Ni precipitates (gamma), is calculated by discrete-dislocation simulations. Two different precipitate sizes and two anti-phase boundary energies are considered. The results of these simulations are compared with corresponding results from gamma-gamma' superalloys (S. Rao, T. A. Parthasarathy, D. Dimiduk, et al., Phil. Mag. 84 3195 (2004)). In general, the results show that precipitation hardening in inverse superalloys is weaker than for regular superalloys. Similar to studies of superalloys, many of these results can be rationalized from the results of simulations on simple homogenized precipitate structures. The Hirsch, Kelly and Ardell precipitation-strengthening model (Metall. Trans. A 16 2131 (1985); Phil. Mag. 12 881 (1965); Trans. Jpn. Inst. Metals 9 1403 (1968).), developed for low-stacking-fault-energy spherical precipitates in a high-stacking-fault-energy matrix, adapted for inverse superalloys, shows qualitative agreement with the simulation results for spherical gamma precipitates.