HIGH-TEMPERATURE TENSILE CREEP OF CMSX-2 NICKEL-BASE SUPERALLOY SINGLE-CRYSTALS

CMSX-2 single crystal specimens were submitted to tensile creep tests along [001] between 923 K (650-degrees-C) and 1223 K (950-degrees-C). The secondary creep rate values are analysed in terms of a Dom creep law. Three temperature domains have to be considered for the values of the apparent parameters in the creep law. Between 973 K (700-degrees-C) and 1073 K (800-degrees-C), the Dorn formalism is no longer valid, since it leads to negative apparent values of the thermal activation energy. From the apparent parameters, a model of the evolution of friction stress with temperature and applied stress is established and effective parameters are determined. The effective parameters are then discussed in terms of deformation mechanisms, taking into account TEM observations of deformed specimens: the anomalous behaviour was thus attributed to the effect of the reinforcing gamma' phase. Maps of active deformation mechanisms are sketched for small strains with reduced coarsening of precipitates.