The creep-rupture properties of the cast superalloy were studied over a wide range of temperatures and stresses. Observations of the dislocation structures during steady-state creep confirmed that the creep mechanism was different in the high- and low-stress regions. The results showed that in the high stress region, shear mechanisms including stacking fault formation and antiphase boundary creation were operative and in the low stress region, a by-passing mechanism occurred by either looping or dislocation climb and glide. With increasing exposure time in the high-temperature low-stress region, dislocations formed networks at γ/γ’ interfaces, as well as inside γ’ particles. The transition in the mode of dislocation-γ’ precipitate interaction from shearing to by-passing was found to depend upon creep conditions (stress and temperature) and microstructural characteristic of the alloy. The present work provided transmission electron microscopic microstructural evidence for a high-temperature by-passing mechanism operating in the superalloy.

Dislocation Network Formation during Creep in Ni-Base Superalloy GTD-111. S.Nategh, S.A.Sajjadi: Materials Science and Engineering A, 2003, 339[1-2], 103-8