A TEM weak-beam study of dislocations in γ' in a deformed Ni-based superalloy

Abstract

The dislocation structure in γ' in deformed single crystals of nickel-based superalloy SRR99 has been observed by weak-beam electron microscopy. Super-dislocations in γ', dissociated into Shockley partials, are continuous across the γ/γ' interface becoming a pair of unit dissociated dislocations in γ'. In γ' most dislocations are screws and their configurations are those of Kear-Wilsdorf locks; the complex stacking faults between the Shockleys lie on {111} and the antiphase boundaries between the superpartials lie on the cube cross-slip plane (010). Despite this sessile configuration of screw dislocation dissociation, the screw dislocations move on the primary slip plane (111) by the propagation of kinks whose four partials lie entirely on (111). Models of the anomalous increase of yield stress at high temperatures that assume a planar dissociation of screws on (111) require reconsideration in the light of these observations.