Influence of Structural Defects, Low-Stability Pre-transitional States and Phase-Structural Transformations on the Stability of Alloys

The relationship between point, planar defects and their complexes and low-stability pre-transition states, phase transitions, structural transformations and alloy stability relative to structural-phase transformations in a low-stability state of systems was studied on the examples of FCC-alloys. Computer simulation methods have shown that in a low-stability state of a condensed system, cooperative interaction of point and planar defects can lead to their ordered arrangement, and the arising static displacement fields can both stabilize the B2-structure and contribute to its instability and martensitic phase transition. In the presence of a certain type of defects in the B2-structure, the latter becomes unstable to shifts of planes of the {111} type along the <111> direction. In the final structure, displacement fields around defects are localized, and the defects themselves organically fit into the structure of the formed phase. Structural defects of the parent phase become natural elements of the structure of the final daughter phase. Structural defects in the low-stability state of the parent phase determine, in fact, the structure of the final daughter phase. It has been shown that in the vicinity of structural-phase transformations in CuPd alloys in the area of 40 at.% Pd, low-stability states are realized, in which a whole range of anomalous phenomena is observed (for example, anisotropy of atomic displacements, concentration inhomogeneities, delamination, heterophase fluctuations, non-linearities in the dependencies of lattice parameters and long-range order parameters, etc.), preparing the system for transformation. The inheritance of defects of the structure by the daughter phase during structural-phase transformations in the pre-transition low-stability state of metallic OCP-system.