L12-phase cutting during high temperature and low stress creep of a Re-containing Ni-base single crystal superalloy

In the present study, we investigate dislocation processes in a Ni-base single crystal superalloy (LEK94) after high temperature and low stress creep. Specimens were creep deformed at 240 MPa and 980 °C to a strain of 20%. We use diffraction contrast transmission electron microscopy (TEM) to show that two γ-channel dislocations with different Burgers vectors combine and form a super dislocation that shears the γ′-particle. This type of cutting event has now been observed for three single crystal superalloys with different alloy chemistry (CMSX-4, CMSX-6 and LEK94 in the present work) and we therefore conclude that it represents a generic elementary dislocation process which governs high temperature (around 1000 °C) and low stress (around 240 MPa) creep. The present paper provides microstructural evidence for this type of cutting processes and discusses the results in the light of previous work published in the literature.