HIGH-RESOLUTION STUDY OF A FCC DO24 INTERFACE IN A WIDMANSTATTEN STRUCTURE/

An air-cooled lamellar Ni-Ni3Ti eutectic alloy exhibits a Widmansttatt en structure in the Ni matrix. The precipitates are thin plates of the hexagonal phase Ni3Ti (DO24). Observations by high resolution electro n microscopy (HREM) of the facetted interfaces (11 (1) over bar)Ni//(0 001)Ni3Ti show the atomic structures of misfit dislocations. A good HR EM image has been studied in detail, enabling the core structure of a misfit dislocation to bi:established for the first time : the dislocat ion is associated with an interfacial ledge with a height of four clos e-packed planes spacings and its Burgers vector is (-1/6)[112]Ni. The theoretical analysis uses the Somigliana dislocation model (Bonnet, Lo ubradou and Penisson, Phys. Rev. Lett., 69, 104, 1992) coupled with th e multislice method to simulate the image contrast.