Paired Dislocations and Their Interactions with γ′ Particles in Polycrystalline Superalloy GH4037

The microstructural characteristics of nickel-based polycrystalline superalloy GH4037 turbine blades that have been in service for 1600 h have been studied by transmission electron microscopy. In particular, emphasis has been placed on paired dislocations and their interactions with γ′ precipitates. Paired dislocations are universal and coexist with Orowan loops occasionally. The attractive force due to anti-phase boundary energy and the repulsive force between two 1/2<110> dislocations act on paired dislocations simultaneously, causing different morphologies of edge dislocations. Since the shear stress required by paired dislocations to cut through γ/γ′ structure is much lower than Orowan stress of single matrix dislocation, the major formation mechanism is dislocation pairing. A large number of paired dislocations slipping on the same {111} plane can form slip band and can shear off γ′ particles, which may directly lead to the formation of microcracks.