The possibility to apply methods of solid state joining for processing large scale billets from microcrystalline materials has been considered. Solid state joining occurs due to development of deformation processes, namely, cooperative grain boundary sliding being the initial stage of solid state joining, and healing of pores due to local grain boundary sliding and replacement of neighbor grains or change of their sites, being the final stage of solid state joining. The efficiency of solid state joining depends on temperature-strain rate conditions of deformation and achieves its maximum under conditions of superplasticity. The strain value providing the strength of the solid state joint being equal to that of the basic material also depends on the initial grain size in the material. The regularities revealed have a universal character and can be applied both to metallic materials and intermetallics and ceramics.