Contents INTRODUCTION 1 STRUCTURAL SUPERPLASTICITY OF POLYCRYSTALLINE MATERIALS 2 CHARACTERISTICS OF GRAIN BOUNDARY ENESEMBLES 3 ORIENTATION-DISTRIBUTED PARAMETERS OF THE POLYCRYSTALLINE STRUCTURE 4 EXPERIMENTAL INVESTIGATIONS OF GRAIN BOUNDARY ENSEMBLES IN POLYCRYSTALS 5 GRAIN BOUNDARY SLIDING IN METALLIC BI-AND TRICRYSTALS 6 PERCOLATION MECHANISM OF DEFORMATION PROCESSES IN ULTRAFINE-GRAINED POLYCRYSTALS 7 PERCOLATION PROCESSES IN A NETWORK OF GRAIN BOUNDARIES IN ULTRAFINE-GRAINED MATERIALS 8 MICROSTRUCTURE AND GRAIN BOUNDARY ENSEMBLES IN ULTRAFINE-GRAINED MATERIALS 9 GRAIN BOUNDARY PROCESSES IN ULTRAFINE-GRAINED NICKEL AND NANONICKEL 10 DURATION OF THE STABLE FLOW STAGE IN SUPERPLASIC DEFORMATION 11 DERIVATION OF COMSTITUTIVE EQUATIONS IN MULTICOMPONENT LOADING CONDITIONS CONCLUSION INDEX