Atomic structure of interphase boundary of an a precipitate plate in a 03B2 Ti-Cr alloy

The atomic structure of the interphase boundary enclosing an a (hcp) precipitate formed from the aY bcc) 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) [111]_03B3transformation dislocations (structural ledges) on (112)_03B3?[1100)_aplanes is accommodated by a set of glissile dislocation loops existing on every sixth (1100)_aplane 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]_aY= (c/2) [0001]_aJ on the risers of the growth ledges at the side facet. The presence of sessile dislocations implies that the migration of a-aY interfaces is a non-conservative process and should accompany the diffusion of substitutional atoms.