Double minimum creep in the rafting regime of a single-crystal Co-base superalloy

Abstract

To investigate whether the formation of rafts in Co-base superalloys has a hardening or softening effect, the single crystal deformation behavior was studied in the high temperature/low stress creep regime. The large positive lattice misfit of the investigated Co-base superalloy led to a pronounced directional coarsening of the microstructure normal to the stress axis during compressive creep at 950°C/150MPa. Two creep minima were observed similar to Ni-base superalloys under tensile creep. Rafting was accompanied by a decreasing creep rate indicating a hardening effect, although cutting of γ′ rafts by partial dislocations under the formation of stacking faults occurred.