Défauts interfaciaux liés au début de la coalescence des précipités γ' du superalliage MC2

Abstract
A heat-treated [001] oriented MC2 superalloy is observed by conventional 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<101> 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<110> 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.