Phase Instability of Nanocrystalline Driven Alloys

A new fundamental phenomenon of phase instability (decomposition) of nanocrystalline alloys and appearance of metastable phases under intensive plastic deformation is considered. Various experimental data illustrating phase transformations of nanocrystalline alloys in the process of deformation treatment are analyzed. The fundamental physical criteria of instability of a solid solution and diffusion equations based on the idea of existence of nonequilibrium vacancy fluxes are formulated. The vacancy fluxes are generated on stress concentrators at grain boundaries in the process of their relaxation. The decomposition appears as a result of the self-consistent interaction of non-equilibrium vacancies with the alloy components having the different diffusion mobility. Within the framework of diffusion model the stability of a regular solid solution in relation to phase decomposition is theoretically investigated. On the base of qualitative and numerical analysis of the diffusion equations the phase instability of the solid solution is demonstrated.