R. R. Unocic, L. Kovarik, M. J. Mills, The Ohio State University, Columbus, OH
The influence of microstructure on the creep rate controlling deformation mechanisms in Ni-base disk superalloy Rene 104 has been investigated through a combination of creep experiments and TEM deformation mechanism characterization. Particular emphasis was placed on the role of the secondary and tertiary γ′ precipitate size scale, volume fraction and γ channel width spacing on the dislocation substructure that formed during creep deformation. A direct comparison was made by testing specimens with different initial microstructures at the same stress (724MPa) and temperature (677ºC). Furthermore, the evolution was tracked by characterizing creep specimens that were interrupted at varying levels of plastic deformation. The TEM results show that the less creep resistant microstructure possessed a greater secondary γ′ size, wider γ channel width, and higher volume fraction of tertiary γ′ precipitates. Deformation in this microstructure commences by way of a/2<110> dislocations that are concentrated in the γ matrix at lower strains, which then transition to a SISF related precipitate shearing mode at larger strains. The more creep resistant microstructure possessed a finer γ channel width spacing, which promoted a/2<110> dislocation dissociation into a/6<112> Shockley partials at lower strains and led to microtwinning at higher strains.
Summary: The influence of microstructure on the creep rate controlling deformation mechanisms in Ni-base disk superalloy Rene 104 has been investigated through a combination of creep experiments and TEM deformation mechanism characterization. Particular emphasis was placed on the role of the secondary and tertiary γ′ precipitate size scale, volume fraction and γ channel width spacing on the dislocation substructure that formed during creep deformation. A direct comparison was made by testing specimens with different initial microstructures at the same stress (724MPa) and temperature (677ºC). Furthermore, the evolution was tracked by characterizing creep specimens that were interrupted at varying levels of plastic deformation. The TEM results show that the less creep resistant microstructure possessed a greater secondary γ′ size, wider γ channel width, and higher volume fraction of tertiary γ′ precipitates. Deformation in this microstructure commences by way of a/2<110> dislocations that are concentrated in the γ matrix at lower strains, which then transition to a SISF related precipitate shearing mode at larger strains. The more creep resistant microstructure possessed a finer γ channel width spacing, which promoted a/2<110> dislocation dissociation into a/6<112> Shockley partials at lower strains and led to microtwinning at higher strains.
