  A systematic study of the compression creep properties of a
single-crystalline Co-base superalloy (Co-9Al-7.5W-2Ta) was conducted at 950
{\deg}C, 975 {\deg}C and 1000 {\deg}C to reveal the influence of temperature
and the resulting diffusion velocity of solutes like Al, W and Ta on the
deformation mechanisms. Two creep rate minima are observed at all temperatures
indicating that the deformation mechanisms causing these minima are quite
similar. Atom-probe tomography analysis reveals elemental segregation to
stacking faults, which had formed in the $\gamma\prime$ phase during creep.
Density-functional-theory calculations indicate segregation of W and Ta to the
stacking fault and an associated considerable reduction of the stacking fault
energy. Since solutes diffuse faster at a higher temperature, segregation can
take place more quickly. This results in a significantly faster softening of
the alloy, since cutting of the $\gamma\prime$ precipitate phase by partial
dislocations is facilitated through segregation already during the early stages
of creep. This is confirmed by transmission electron microscopy analysis.
Therefore, not only the smaller precipitate fraction at higher temperatures is
responsible for the worse creep properties, but also faster diffusion-assisted
shearing of the $\gamma\prime$ phase by partial dislocations. The understanding
of these mechanisms will help in future alloy development by offering new
design criteria.
