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

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.

Microstructural Transformation and Enhanced Strength of Wire‐Feed Electron‐Beam Additive Manufactured Ti–6Al–4V Alloy Induced by High‐Pressure Torsion

“…In addition, the structure and state of the grain boundaries, which usually have a nonequilibrium structure and contain a significant amount of grain boundary segregations and precipitates, are also a crucial issue. [47,48] In turn, it is known that grain size can affect the k HP coefficient in the Hall-Petch relation. [48,49] With grain sizes smaller than 50-100 nm, the Hall-Petch curve often deviates from the linear relationship and its slope can become even negative.…”

“…[47,48] In turn, it is known that grain size can affect the k HP coefficient in the Hall-Petch relation. [48,49] With grain sizes smaller than 50-100 nm, the Hall-Petch curve often deviates from the linear relationship and its slope can become even negative. [48,49] This effect is probably caused by the state of the grain boundaries after SPD treatment.…”

“…[48,49] With grain sizes smaller than 50-100 nm, the Hall-Petch curve often deviates from the linear relationship and its slope can become even negative. [48,49] This effect is probably caused by the state of the grain boundaries after SPD treatment. It may also influence the grain size contribution to the high-strength state.…”

Electroplastic Effect during Tension and Bending in Duplex Stainless Steel

“…The influence of loading rate on hardening is a well-known phenomenon in coarsegrained metallic materials [27]. In general, an increase in deformation rate leads to an increase in the resistance of metals to deformation.…”

Design and Development of High-Strength and Ductile Ternary and Multicomponent Eutectoid Cu-Based Shape Memory Alloys: Problems and Perspectives

“…However, only TiNi-based alloys (based on titanium nickelide) are distinguished by a unique combination of the strengthand plastic properties and SM effects and are increasingly being used in engineering and medicine. Previously, it was found that their fine-and ultrafine-grained (FG and UFG) structure leads to improvements in the strength, plastic, and fatigue characteristics of SM alloys [27][28][29][30][31][32]. The special UFG structure of TiNi-based alloys is provided by various thermal deformation technologies using severe megaplastic deformation (SMD) methods, including multi-pass equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) [33][34][35][36][37][38][39][40], rolling, drawing into strips, rods or wire [41].…”