材料期刊网

Low cycle isothermal mechanical fatigue testing K40S cobalt-base superalloy was carried out at 700 and 900degreesC with total strain amplitude from +/-0.1 to +/-1.0 pct. Correlations between microscopic cyclic deformation and cycle stress response with various microstructural phenomena were enabled through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), detailing the deformation substructure and carbide precipitation. The results show that K40S superalloy exhibited cyclic stress response of cyclic hardening at 700degreesC, and of initial hardening followed by softening at 900degreesC. In addition, at both temperatures, cyclic hardening during cycle deformation increased with increasing strain amplitude, while the fatigue lifetime decreased. The cyclic stress response behavior can be rationalized based on the mechanisms associated with dislocation-dislocation interactions, dislocation-precipitate (M23C6) interactions and interactions between solute atoms and dislocations. (C) 2002 Elsevier Science B.V. All rights reserved.