Atomic structure of interphase boundary of an a precipitate plate in a p Ti-Cr alloy

摘要

The atomic structure of the interphase boundary enclosing an a (hep) precipitate formed from the p (bec) matrix in a Ti-Cr alloy was examined. All the interfaces of an a lath exhibit continuity of atomic planes between the matrix and the precipitate and thus are considered to be coherent or semicoherent. Such observations imply that there is an atomic site correspondence during transformation. The shear component of the transformation strains arising from the passage of (a/12) [lll]p transformation dislocations (structural ledges) on (112))/1100)a_planes is accommodated by a set of glissile dislocation loops existing on every sixth (Il00)a plane at the side facet and the edge of an a lath. The volumetric component of the transformation strain is accommodated by a set of sessile misfit dislocations (b = (a/2)[110]p = (c/2) [0001]) on the risers of the growth ledges at the side facet. The presence of sessile dislocations implies that the migration of a-(3 interfaces is a non-conservative process and should accompany the diffusion of substitutional atoms.