Deformation mechanisms at intermediate creep temperatures in the Ni-base superalloy René 88 DT

Creep deformation substructures in superalloy René 88 DT have been investigated at two applied stress levels after small-strain (0.5%) creep at 650 °C using conventional and high resolution transmission electron microscopy. Clear differences in creep strength and substructures have been observed as a function of applied stress. It has been established that at intermediate temperatures microtwinning caused by the passage of Shockley partial dislocations on successive {1 1 1} planes is the dominant deformation process at low applied stress. At higher applied stress the mechanism changes to planar shearing of the matrix by 1/2〈1 1 0〉 unit dislocations and Orowan looping of the precipitates. Detailed experimental evidences for these operating processes are shown and possible explanation is provided.