材料期刊网

An investigation has been carried out on the cyclic deformation and changes in microstructure of a directionally solidified cobalt-base superalloy. The tests are conducted at 700 degrees C and 850 degrees C in air under different total strain amplitudes. The alloy tested at 700 degrees C exhibits an initial hardening, a short saturation stage and an evident secondary hardening, while the alloy at 850 degrees C suffers continuous cyclic hardening until fracture. TEM examinations indicate that the initial hardening of the alloy at 700 degrees C is caused by the pile-ups of dislocations and stacking faults at the stacking fault intersections, while the stress saturation is due to the weakening of obstacles against the dislocation movement. The secondary hardening has a contribution from the formation of sessile dislocation tangles. The early stage of continuous hardening of the alloy at 850 degrees C is related to the pile-ups of dislocations and stacking faults at the intersections, and the later stage is controlled by the interaction between precipitates and dislocations.