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We suggest a model, which describes the effect of grain boundary relaxation on the annealing-induced hardening in ultrafine-grained metals. Within the model, grain boundary relaxation during annealing is accompanied by a decrease in the number of grain boundary dislocation sources. The exhaustion of easily activated grain boundary dislocation sources results in the activation of harder grain boundary dislocation sources and/or repetitive action of the same dislocation sources. This gives rise to an increase in the strain hardening rate that can lead to an increase in the ultimate strength of ultrafine-grained solids. The results of the model agree with available experimental data.

A theoretical model describing effect of grain size distribution in the metal matrix of metal-graphene composite on its yield strength. The model describes the initial stage of plastic deformation in metal-graphene composites and takes into account both dislocation mechanisms of plasticity and the process of grain boundary sliding. The yield strength of aluminum-graphene composite was calculated depending on the average grain size of the matrix and the volume fraction of graphene. Our analysis shows that the presence of a dispersion in the grain size distribution of the metal matrix decreases the yield stress so special attention should be paid to reducing this dispersion during synthesis of the composite.

A model is proposed that describes the development of individual and multiple necks in superplastically deformed materials. Within the model, the examined samples have the form of round bars and are subjected to tensile superplastic deformation without strain hardening. It is demonstrated that neck development and necking-induced failure occur faster with a decrease in strain rate sensitivity and/or an increase in the fraction of the sample length occupied by necks. This means that high values of strain to failure observed in small specimens of superplastically deformed ultrafine-grained metals and alloys, where diffuse necking happens in the whole specimen, can be significantly reduced in larger specimens where the necking regions occupy only a small part of the sample.