The saturation state of strength and ductility of bimodal nanostructured metals

Abstract

Bimodal nanostructured metals have ultrahigh strength and good ductility, but their values are highly dependent on the cohesive strength of both phases. To explore this dependence, we apply the strain-gradient plasticity theory to the nanograined phase and a cohesive finite element method to determine the overall fracture process. The results show that when the cohesive strength of both phases reaches certain level, the stress-strain curves will reach a saturation state. This finding points to the significance of designing the cohesive strength to such a critical value so that the maximum strength and ductility could be attained.

Nanostructured Metals with an Excellent Synergy of Strength and Ductility: A Review

“…Therefore, the toughening of nanostructured metals has aroused the interest of researchers. In the recent 20 years, in order to improve their ductility, researchers have multilevel-constructed the composition, size, and distribution of different nanostructures, and some significant achievements have been made: (1) the bimodal structure is the introduction of a certain volume of micron-leveled coarse grains into the nanograined metal, and the resulting metal has the strength of the nanograined metal and the plasticity of the coarse-grained metal, i.e., good mechanical properties [ 17 , 18 , 19 , 20 ]; (2) by introducing nanotwinned (NT) structure inside the grains, the metal exhibits excellent mechanical properties, including high strength, plasticity, work-hardening rate, and fatigue performance, due to the relatively low interface energy and coherent characteristics of twin boundaries (TBs) [ 21 , 22 , 23 , 24 ]; (3) microstructure in which grain size, structure, and/or composition continuously change from nanometer-scale to micrometer-scale, i.e., a gradient nanostructure, has the performance advantages of each scale structure, so as to simultaneously realize strengthening and toughening [ 25 , 26 , 27 , 28 ]; (4) the supra-nano-dual-phase (SNDP) nanostructure consists of two phases with differences in structure or composition, i.e., heterogeneous two-phase nanostructure, and not only exhibits excellent mechanical properties, but also presents other functional properties, such as soft magnetic properties and thermal stability [ 29 , 30 ].…”

Effect of Annealing Temperature on the Microstructure and Mechanical Properties of High-Pressure Torsion-Produced 316LN Stainless Steel

“…As mentioned, the annealing temperature has a great influence on microstructure evolution and mechanical properties of SPD-produced materials. In general, the annealing process can promote grain recrystallization, resulting in the reduction in strength [ 34 , 35 , 36 , 37 ]. However, unexpected strengthening was observed in the annealed HPT-produced 316L steels [ 31 ].…”

Microstructure‐Property Relations in the Tensile Behavior of Bimodal Nanostructured Metals

“…[34] It turns out that the CFEM is feasible to investigate the fracture behavior of engineering materials. [35][36][37][38] By CFEM, the microcrack initiation and propagation can be vividly tracked; [35][36][37][38] the interface effects can also be revealed. [34,38] Comparing with the 2D numerical simulations, the 3D numerical simulations have been verified to have superiority in investigating the fracture behavior of materials.…”

“…The overall strength and ductility is saturated when the cohesive strength of interfaces surpasses a certain level . It turns out that the CFEM is feasible to investigate the fracture behavior of engineering materials . By CFEM, the microcrack initiation and propagation can be vividly tracked; the interface effects can also be revealed …”