  This work deals with an investigation of general principles of
superplasticity (SP) in deformed materials. It is shown that a non-linear, wave
plastic deformation is the basic process for all plastic deformation phenomena,
it makes an individual contribution into these phenomena, allows describing
them from the same standpoints, and offers a way to follow the relationship
between the physics of defects and the mechanics of plasticity. It is to be
noted that macro and meso defects - discontinuities in the vector fields of
macro and meso elastic displacements, are no less fundamental than are the
microdefects - dislocations and disclinations, it is the latter which form the
process of localized macrodeformation. General mechanisms of this process are
analyzed in this study. Constitutive equation of superplastic state is
obtained, which relates the strain rate, its rotational modes, local
irreversible stresses, temperature, and density of heat and mass transfer.
Special cases and their derived relations are analyzed. It is shown that SP is
determined by plastic equilibrium concurrent with the composition and structure
fluctuations. An expression is obtained for the superplastic flow velocity,
containing three terms: velocity of wave plastic macroprocess, increased by
fluctuations, velocity prescribed by the gradient of external sources
(diffusion, etc.), and velocity of the delayed intragranular slip. It should be
noted that transformation is a characteristic and necessary feature of SP flow.
In the absence of transformations, deformation occurs via creep. Fragmentation
of the deforming region and grain-boundary sliding (GBS) are discussed and so
are their mechanisms and characteristic features. Formulas are derived for the
strain rate under conditions of GBS and the reasons for its non-monotonic
dependence on grain size, applied stresses and temperature are analyzed.
