Crystal plasticity modeling the deformation in nanodomained heterogenous structures
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Crystal plasticity modeling the deformation in nanodomained heterogenous structures Tianju Chen1
Caizhi Zhou1,a)
1
Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, Missouri 65409, USA Address all correspondence to this author. e-mail: [email protected]
a)
Received: 26 October 2018; accepted: 6 February 2019
Nanodomained heterogenous structures characterized by randomly dispersed nanograins (NGs) embedded in the coarser grains (CGs) have demonstrated an exciting potential to break the strength–ductility trade-off, providing high strength without the loss of ductility. Here, using a combination of discrete crystal plasticity finite element (discrete-CPFE) model and dislocation density-based CPFE model, we study the effects of grain size, volume fraction of nanograins on the strength and deformation in nanodomained materials. Our analysis shows that the overall flow stresses of nanodomained samples are equal or higher than the strengths predicted by rule of mixtures. Smaller NGs or higher volume fraction of NGs can make the nanodomained samples stronger, as they can be more effective to promote the dislocation accumulations inside the CGs and eventually raise the critical resolved shear stress for each slip system during the plastic flow. Areas surrounding NGs stored higher dislocation densities and less plastic strain, due to the restricted dislocation motion. Furthermore, NGs grain embedded in the CGs can effectively reduce the anisotropy of strength in the nanodomained samples.
Introduction Over the past 30 years of research shows that the nanocrystalline (NC) materials usually have high strength and hardness. Without changing the material chemical composition, the strength and hardness of NC materials can be several times or even dozens of times as that to the same component of coarse grain (CG) materials [1, 2, 3, 4, 5, 6]. However, with the significant increment of strength and hardness, the plasticity and toughness of NC materials drop substantially, and work hardening ability disappears. The structural instability and the performance deterioration restrict the performance and applications of NC materials. With the process of new nanotechnologies, building nanostructures into architecture can effectively overcome the drawback of NC materials at the same time giving full play to the advantages of their performance. There are several examples for the architectured NC materials, such as the gradient nanograined structure [1, 2, 3, 4, 5, 6], heterogenous lamella structure [7, 8, 9, 10], bimodal structure [8, 11, 12, 13], and nanodomained structure [14]. These materials have a common feature that a remarkable difference in the strength
ª Materials Research Society 2019
between different domains, while the sizes and shape of the domains may vary significantly. The gradient nanostructure refers to the structure of the unit size, such as grain size or the layer thickness on the space gradient change from the nanoscale continuously increase to macroscale. The essence
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