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 l aw. 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 Between 973 K (700-degrees-C ) and 1073 K (800-degrees-C), the Dorn formalism is no longer valid, s ince it leads to negative apparent values of the thermal activation en ergy. From the apparent parameters, a model of the evolution of fricti on stress with temperature and applied stress is established and effec tive parameters are determined. The effective parameters are then disc ussed in terms of deformation mechanisms, taking into account TEM obse rvations of deformed specimens: the anomalous behaviour was thus attri buted to the effect of the reinforcing gamma' phase. Maps of active de formation mechanisms are sketched for small strains with reduced coars ening of precipitates.