  Nanoscale inhomogeneities are typical for numerous metallic alloys and
crucially important for their practical applications. At the same time,
stabilization mechanisms of such a state are poorly understood. We present a
general overview of the problem, together with a more detailed discussion of
the prototype example, namely, Guinier-Preston zones in Al-based alloys. It is
shown that coherent strain due to a misfit between inclusion and host crystal
lattices plays a decisive role in the emergence of the inhomogeneous state. We
suggest a model explaining formation of ultrathin plates (with the thickness of
a few lattice constants) typical for Al-Cu alloys. Discreteness of the array of
misfit dislocations and long-ranged elastic interactions between them are the
key ingredients of the model. This opens a way to a general understanding of
the nature of (meta)stable embedded nanoparticles in practically important
systems.
