Interface defects associated with the coalescence of γ' precipitates of the MC2 superalloy

A heat-treated 001 oriented MC2 superalloy is observed by conventiiional and high resolution electron microscopy (HREM) to characterize the defects associated with the early stage of the coalescence phenomenon. From a HREM image of two contiguous γ' precipitates and a suitable image treatment, a rigid shift 1/2 left angle 101 right angle is derived between the two ordered lattices. Coalescence is more in progress near subgrain boundaries than in dendrite cores where the dislocation density is close to zero. 1/2 left angle 110 right angle matrix dislocations sweep the γ corridors and interact with the γ/γ' interfaces they bend locally to produce interfacial ledges (15 to 22 nm in height). All the observed interfacial dislocations have their edge components relaxing the coherency stresses. (orig.)