On the creep behavior at 1033 K of new generation single-crystal superalloys

The various parameters influencing the creep behavior at 1033 K of the MC544 and MC534 new generation single crystal nickel-based superalloys were analyzed in comparison with that of the first generation AM1 superalloy. A clear relationship was evidenced between the main deformation process and the amplitude of primary creep stage. A large amplitude of primary creep is always associated with heterogeneous deformation resulting from the low mobility of the a/2〈1 1 0〉 perfect matrix dislocation and shearing of γ′ precipitates by 〈1 1 2〉{1 1 1} slip. On the contrary, limited amplitude of primary creep is systematically associated with homogeneous deformation within the γ matrix channels by 〈1 1 0〉{1 1 1} slip. The differences of γ/γ′ microstructure, stacking fault energy of the γ phase, antiphase boundary energy, lattice mismatch amplitude and solid solution strengthening have been taken into account to explain the transition between these two deformation modes. The comparison between the respective solid solution strengthening effects in the γ and γ′ phases of the AM1 and MC544 alloys allows to explain their difference in creep behavior. On the other hand, the beneficial role of a high negative lattice mismatch regarding the creep behavior at 1033 K was clearly evidenced in the MC534 alloy.