On the shearing mechanism of γ′ precipitates by a single (a/6)⟨112⟩ Shockley partial in Ni-based superalloys

The weak-beam technique of transmission electron microscopy has been used to analyse a new shearing configuration of γ′ precipitates after creep at 700°C of a Ni-based superalloy for gas turbine discs. The shearing configurations are made up of superlattice extrinsic stacking faults, matrix stacking faults and individual (a/6)⟨112⟩ Shockley dislocations. This mechanism is initiated by the decorrelated movement of the two Shockley partials of a single (a/2)⟨110⟩ matrix dislocation. The propagation of the leading partial creates this shearing process. This phenomenon that occurs in small γ channels owing to the flexibility of dislocations can be used to evaluate microstructural evolutions during ageing in the alloy.