MASS TRANSFER MECHANICS PROVIDING ULTRAFINE-GRAINED STRUCTURE FORMATION IN METALS AND ALLOYS

The article considers the deformation processes of ultrafine-grained (UFG) structure formation in polycrystalline materials exhibiting superplastic properties, and the theoretical methods of molecular dynamics (MD) and Monte Carlo (MC) for simulating the formation of a nanocrystalline structure. The history
of the interest in grain refinement, caused by the influence of grain size on the strength and superplastic properties of metals and alloys, is briefly described. It is shown that mass transfer underlies the formation of UFG structures, including nanocrystalline ones. In the case of deformation refinement, a new technique for calculating the degree of deformation required to refine the microstructure is proposed. In the case of
theoretical description of nanograin formation using MD and MC methods, the concepts of grain boundary engineering in polycrystalline materials are used, leading to selective mass transfer of grain-boundary atoms forming a dense network of nanoboundaries with high strength and deformation properties. The paper discusses methods of severe plastic deformation and the mechanisms of superplastic deformation.