Functional and Multifunctional Properties of UFG Metallic Materials

The formation of ultrafine grains with nanostructural features in metallic materials by SPD processing can provide superior mechanical and, simultaneously, functional properties of metals and alloys, for example, high strength and electrical conductivity in Cu and Al alloys, enhanced fatigue endurance and high corrosion and erosion resistance in Ti alloys and many other so-called multifunctional properties. This chapter demonstrates that the level of the above properties is determined by small grain size, nonequilibrium grain boundaries with high density of grain boundary dislocations, nanoscale grain boundary segregations and precipitations, etc. Changes in the physical properties of UFG materials are associated with the comparability of grain sizes and characteristics, including the free path length of electrons and the size of magnetic domains. In particular, nanocrystalline magnetic hard materials are characterized by high coercivity, which is due to the interaction of crystal structure defects with the walls of the magnetic domains during the movement of the latter. Nanocrystalline soft magnetic materials are characterized by high magnetic inductive capacity, low coercive force, and relatively high saturation magnetization. The enhancement of the above properties is the result of the domain size becoming smaller than the grain size. UFG materials demonstrate enhanced biomedical properties, but the level of biocompatibility is strongly influenced by the substrate surface quality. Etching and formation of bioactive coatings contribute to the increase of biocompatibility. The formation of UFG structures has a great positive effect on the manifestation of the shape memory effect and the superelasticity of materials. For example, the reactive force increases and the temperature range of the shape memory effect decreases. Chapter 3 not only describes numerous examples of achieving unique multifunctional properties of nanostructured materials obtained by SPD techniques but also discusses their physical origin related to the influence of nanostructuring on the deformation and transport mechanisms that determine the properties of nanomaterials.