Effect of geometrical distribution of sub-grain boundaries on creep properties of Ni-based superalloys

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Geometrically required dislocations are distributed at sub-grain boundaries that corresponds to interfaces of dendrites grown in Ni-based superalloys. In the present study, we have performed compressive creep tests to observe the development of creep dislocation networks at gamma/gamma-prime interfaces, and of parallel raft structure. When a compressive stress is applied along tothe growth direction, the magnitude of primary creep is very small compared with that applied perpendicular to the growth direction. We have constructed a creep testing machine that can use a very small specimen without dislocation networks in it.