The Superstrength of Nanostructured Metallic Materials: Their Physical Nature and Hardening Mechanisms

Abstract

Abstract Ultrafine grained (UFG) metallic materials obtained by severe plastic deformation (SPD) typically exhibit very high strength properties, whose values are much higher than those predicted by the well-known Hall–Petch relation. Our studies show that the basis for this to occur is that SPD not only forms the UFG structure, but also leads to the formation of other nanostructural features, such as dislocation substructures, nanotwins, and nanosized precipitates of second phases, which additionally contribute to strengthening of materials. At the same time, this analysis of hardening mechanisms indicates that the structure and condition of grain boundaries, namely, their nonequilibrium state and the presence of grain boundary segregations, also substantially contribute to hardening. Taking this into consideration, approaches are discussed to achieve very high strengths in metallic materials by SPD.