STRUCTURAL LEDGES AT PRECIPITATE MATRIX INTERFACES IN A (NI, CO) SUPERALLOY - ATOMIC STRUCTURES AND ELASTIC FIELDS

The broad faces of plate-like DO19 precipitates of a (Ni, Co) base sup eralloy are decorated with triangular networks of linear singularities (LS's) accomodating the 2.5% isotropic length misfit in the atomicall y dense planes (111)fcc parallel-to(0001)DO19. High-resolution electro n microscopy images depict the detailed atomic cores of two of these L S's and show that they are associated with ledges of two (111) spacing s in height. The elastic fields surrounding the IS's are analyzed by u sing both multislice computations and the Somigliana dislocation model in anisotropic elasticity theory. As a result, the Burgers-vector con tent of the observed ledges is found to be 1/6[112] vectors.