1 STRUCTURAL SUPERPLASTICITY OF POLYCRYSTALLINE MATERIALS 1
1.1．Structural levels,spatial scales and description levels 1
1.2．Structural superplasticity:from the combination of mechanisms to cooperative grain boundaries sliding 5
1.3．Structural superplasticity:from meso-description to nacrocharacteristics 14
References 18
2 CHARACTERISTICS OF GRAIN BOUNDARY ENESEMBLES 20
2.1．Crystal geometry and structure of intercrystalline boundaries 20
2.1.1．Methods for describing the structure of the grain boundaries 20
2.1.2．Analytical representation of the basis of the coincident-site lattice for cubic lattices 26
2.2．Special grain boundaries in the monoclinic lattice 32
2.3．Description of the grain boundary misorientation distribution(GBMD) 37
2.4．Computer model of a polycrystal:a calculation algorithm 42
References 47
3 ORIENTATION-DISTRIBUTED PARAMETERS OF THE POLYCRYSTALLINE STRUCTURE 49
3.1．The distribution function of the grains with respect to crystallographic orientations:calculation methods 49
3.2．Relationship between the grain boundary misorientation distribution and the ODF 53
3.3．Correlation orientation of adjacent grains:the concept of the basis spectra of misorientation of the grain boundaries 59
3.4．Modelling the misorientation spectra of the grain boundaries in the FCC crystals with modelling ODF 65
References 74
4 EXPERIMENTAL INVESTIGATIONS OF GRAIN BOUNDARY ENSEMBLES IN POLYCRYSTALS 75
4.1．Diffraction methods of measuring misorientation 75
4.1.1．Methods of measuring the misorientation of two adjacent grains 75
4.1.2．The experimental measurement error 80
4.2．Experimental spectra of the grain boundaries in FCC polycrystals 89
4.3．Orientation distribution function in Ni-Cr alloy:experimental and modelling GBMDs 93
4.3.1．Orientation distribution function in Ni-Cr alloy and stainless steels 93
4.3.2．Modelling spectra of the misorientation of the grain boundaries in Ni-Cr alloy and AISI stainless steels:comparison with the experimental results 99
4.4．Special features of the grain boundaries in the FCC materials with a high stacking fault energy 104
4.4.1．Rolling and annealing texture of aluminium 104
4.4.2．Grain boundary ensembles in aluminium:experiments and modelling 107
References 117
5 GRAIN BOUNDARY SLIDING IN METALLIC BI-AND TRICRYSTALS 119
5.1．Dislocation nature of grain boundary sliding(GBS) 119
5.2．Formulation of the model of stimulated grain boundary sliding 125
5.3．Formal solution and its analysis 132
5.4．Special features of pure grain boundary sliding 136
5.5．Local migration of the grain boundary as the mechanism of reorganisation of the triple junction:weak migration approximation 140
5.6．Variance formulation of the system of equations for the shape of the boundary and pile-up density 149
5.7．The power of pile-ups of grain boundary dislocations 155
References 160
6 PERCOLATION MECHANISM OF DEFORMATION PROCESSES IN ULTRAFINE-GRAINED POLYCRYSTALS 162
6.1．Percolation mechanism of the formation of a band of cooperative grain boundary sliding 162
6.2．Conditions of formation of CGBS bands as the condition of realisation of the superplastic deformation regime 167
6.3．Shear rate along the CGBS band 170
6.4．Kinetics of deformation in CGBS bands 172
6.5．Comparison of the calculated values with the experimental results 176
References 186
7 PERCOLATION PROCESSES IN A NETWORK OF GRAIN BOUNDARIES IN ULTRAFINE-GRAINED MATERIALS 187
7.1．Effect of grain boundaries on oxidation and diffusion processes in polycrystalline oxide films 187
7.2．High-resolution electron microscopy of zirconium oxide:grain clusters,surrounded only by special boundaries 191
7.3．Effect of the statistics of the grain boundaries on diffusion in zirconium oxide 196
7.4．Special features of oxidation kinetics under the effect of stresses at the metal/oxide boundary 202
7.5．Texture and spectrum of misorientation of the grain boundaries in an NiO film on(100)and(111)substrates:modelling and experiments 208
References 222
8 MICROSTRUCTURE AND GRAIN BOUNDARY ENSEMBLES IN ULTRAFINE-GRAINED MATERIALS 224
8.1．Methods of producing ultrafine-grained and nanostructured materials by severe plastic deformation 224
8.2．Effect of the parameters of quasi-hydrostatic pressure on the microstructure and grain boundary ensembles in nickel 231
8.3．Spectrum of misorientation of grain boundaries in ultrafine-grained nickel 236
8.4．Advanced methods of automatic measurement of the grain boundary parameters 237
8.5．The misorientation distribution of the grain boundaries in ultrafine-grained nickel:experiments and modelling 239
References 247
9 GRAIN BOUNDARY PROCESSES IN ULTRAFINE-GRAINED NICKEL AND NANONICKEL 249
9.1．Grain growth kinetics in ECAP specimens 250
9.2．Activation energy and stored enthalpy in ultrafine-grained nickel 257
9.3．Evolution of the microstructure and texture in HPT nickel in annealing 264
9.4．Superplasticity of nanocrystalline nickel 267
References 274
10 DURATION OF THE STABLE FLOW STAGE IN SUPERPLASTIC DEFORMATION 276
10.1．Superplastic capacity and the rate sensitivity parameter 276
10.2．Description of thickness differences of a flat specimen in tensile deformation 279
10.3．Formation of thickness difference as a random process 280
10.4．Absorption condition and the equation for limiting strain 284
10.5．Some properties of limiting strain 290
References 292
11 DERIVATION OF CONSTITUTIVE EQUATIONS IN MULTICOMPONENT LOADING CONDITIONS 293
11.1．From the deformation mechanism to constitutive equations 293
11.2．Kinematics of polycrystalline continuum 296
11.3．Strain rate tensor determined by shear along the CGBS bands 299
11.4．Degenerate cases and variants of coaxiality of the tensors 304
References 307
CONCLUSION 309
INDEX 311