HIGH-RESOLUTION MICROSCOPY OF A SEMI-COHE RENT MU-PHASE GAMMA-GAMMA'-PHASE INTERFACE

Among different orientation relationships between rhomboedral mu preci pitates and the gamma-gamma' two-phase medium of a nickel base superal loy, one is found appropriate for the observation of the heterointerfa ce by high resolution electron microscopy. Misfit dislocations (MD's) are observed, associated with interfacial ledges. They accommodate a 0 .6 % length misfit and a small long range angular departure equal to 1 .9 degrees between the planes (542)(mu) and (113)gamma'. The relative position of the crystals along the interface facets has been determine d, as well as the common Burgers vector of the MD's. A computer analys is of a MD image, observed at near-atomic scale, demonstrates that the experimental elastic displacement field of the surrounding atomic col umns is in good agreement with the dislocation-ledge theory developed by the authors (Phys. Rev. Lett., 1992, 69, 104-107).