Ultra‑fine grained and nanocrystalline materials belong to an important group of modern materials with unusual properties that are very attractive for different structural and functional applications. Modern techniques of preparation of these materials are based on the imposition of very high strains leading to exceptional grain refinement without any significant change of the overall dimensions. High hydrostatic pressures are applied during these processes which introduce high densities of lattice defects (e.g. dislocations or vacancies) and result in the formation of special structures. Materials fabricated by these techniques, called severe plastic deformation, exhibit several unique properties including very high‑strength, ductility and fatigue endurance, increased superplastic capabilities as well as multifunctional behaviour when materials exhibit enhanced functional (electric, magnetic, corrosion, etc.) and mechanical properties.
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