Dislocation-Based Deformation Mechanisms in Metallic Nanolaminates

The appeal of nanolayered materials from a mechanical viewpoint is that, in principle, plastic deformation can be confined to small volumes of material by Controlling both the frequency and magnitude of obstacles to dislocation motion. As we shall see, the spacing of obstacles can be used to impart large plastic anisotropy and work hardening. However, how strong can such materials be made as layer thickness (and therefore obstacle spacing) is decreased to the nanoscale level? In perspective, large, micron-scale, polycrystalline materials generally display improved yield strength (and fracture toughness) as grain size is decreased. This behavior at the micron scale can be explained via modeis that are built on two assumptions: (1) the strength of obstacles to crystal slip is sufficiently large to require pileups of numerous dislocations in order to slip past them; and (2) the strength of such obstacles does not change, even if their spacing is decreased. The modeling presented here shows that these assumptions may break down at the nanometer scale. The result is that there is a critical layer thickness in the nanometer range, below which improvement in strength does not occur.Our discussion to follow briefly outlines a more macroscopic, micron-scale approach to determine yield strength, and then contrasts that with a sequence of events leading up to yield in nanolayered materials. We also address whether nanoscale materials are expected to exhibit more uniform or coarse slip than micron-scale materials. Finally, a semi-quantitative model of yield strength is developed which requires, as input, the strength of an interface to crystal slip transmission across it. We discuss several contributions to the interfacial strength and apply the theory to demonstrate a peak in strength for a 50 vol% Cu-50 vol% Ni multilayered sample.

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Multiscale modelling of the plastic anisotropy and deformation texture of polycrystalline materials

European Journal of Mechanics - A/Solids ◽

10.1016/j.euromechsol.2006.05.003 ◽

2006 ◽

Vol 25 (4) ◽

pp. 634-648 ◽

Cited By ~ 76

Author(s):

Paul Van Houtte ◽

Anand Krishna Kanjarla ◽

Albert Van Bael ◽

Marc Seefeldt ◽

Laurent Delannay

Keyword(s):

Plastic Anisotropy ◽

Deformation Texture ◽

Multiscale Modelling ◽

Polycrystalline Materials

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Haasen plot analysis of the Hall–Petch effect in Cu/Nb nanolayer composites

Journal of Materials Research ◽

10.1557/jmr.1999.0059 ◽

1999 ◽

Vol 14 (2) ◽

pp. 407-417 ◽

Cited By ~ 31

Author(s):

M. F. Tambwe ◽

D. S. Stone ◽

A. J. Griffin ◽

H. Kung ◽

Y. Cheng ◽

...

Keyword(s):

Activation Analysis ◽

Grain Boundaries ◽

Layer Thickness ◽

Rate Sensitivity ◽

Dislocation Motion ◽

Rate Dependent ◽

Plot Analysis ◽

Sensitivity Data ◽

Simple Models

We investigate the effects of layer thickness (t) on hardness (H) and rate sensitivity of the hardness (∂H/∂ ln ) in 1 μm-thick Cu/Nb nanolayer composites. For t < 10 nm, we find that H correlates with t according to H = H0 = H1t-1/2, suggestive of a Hall–Petch mechanism with layer interfaces replacing grain boundaries as barriers against dislocation motion. The measured levels of ∂H/∂ ln clearly indicate the operation of bulk-like dislocation mechanisms consistent with a Hall–Petch mechanism. However, based on a Haasen-plot activation analysis, it appears that the Hall–Petch coefficient, H1, is strongly rate-dependent, inconsistent with a conventional Hall–Petch mechanism. For specimens with t < 10 nm there is a saturation in hardness, but the rate sensitivity data indicate no clear evidence of a corresponding change in mechanism. Simple models are proposed.

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The Correlation Length: A Measure of Inhomogeneities in Polycrystalline Materials

12th International Conference on Nuclear Engineering, Volume 1 ◽

10.1115/icone12-49603 ◽

2004 ◽

Author(s):

Igor Simonovski ◽

Marko Kovacˇ ◽

Leon Cizelj

Keyword(s):

Grain Size ◽

Finite Element ◽

Stress Field ◽

Yield Strength ◽

Correlation Length ◽

Shear Bands ◽

Polycrystalline Materials ◽

Internal Length ◽

Correlation Lengths ◽

Average Grain Size

This paper deals with the correlation length estimated from a mesoscopic model of a polycrystalline material. The correlation length can be used in some macroscopic material models as a material parameter that describes the internal length. It can be estimated directly from the strain and stress fields calculated from a finite-element model, which explicitly accounts for the selected mesoscopic features such as the random orientation, shape and size of the grains. The crystal plasticity material model was applied during the finite-element analysis. Different correlation lengths were obtained depending on whether the strain or the stress field was used. The correlation lengths also changed with the macroscopic load. While the load is below the yield strength the correlation lengths are constant, and of the order of the average grain size. Increasing the load above the yield strength creates shear bands that temporarily increase the values of the correlation lengths calculated from the strain fields. With a further load increase the correlation lengths decrease slightly below the average grain size. The correlation lengths calculated from the stress field are smaller than the ones calculated from the strain field. However, with the exception of the load region where significant shear bands appear, both seem to follow the same qualitative rules.

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The Hall–Petch and inverse Hall–Petch relations and the hardness of nanocrystalline metals

Journal of Materials Science ◽

10.1007/s10853-019-04160-w ◽

2019 ◽

Vol 55 (7) ◽

pp. 2661-2681 ◽

Cited By ~ 18

Author(s):

Sneha N. Naik ◽

Stephen M. Walley

Keyword(s):

Grain Size ◽

Yield Strength ◽

Nanocrystalline Materials ◽

Grain Boundary Sliding ◽

Polycrystalline Materials ◽

Size Dependent ◽

Physical Mechanisms ◽

Grain Sizes ◽

Boundary Sliding ◽

Fundamental Physical

AbstractWe review some of the factors that influence the hardness of polycrystalline materials with grain sizes less than 1 µm. The fundamental physical mechanisms that govern the hardness of nanocrystalline materials are discussed. The recently proposed dislocation curvature model for grain size-dependent strengthening and the 60-year-old Hall–Petch relationship are compared. For grains less than 30 nm in size, there is evidence for a transition from dislocation-based plasticity to grain boundary sliding, rotation, or diffusion as the main mechanism responsible for hardness. The evidence surrounding the inverse Hall–Petch phenomenon is found to be inconclusive due to processing artefacts, grain growth effects, and errors associated with the conversion of hardness to yield strength in nanocrystalline materials.

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Shear deformation mechanical performance of Ni–Co alloy nanoplate by molecular dynamics simulation

Modern Physics Letters B ◽

10.1142/s0217984921503231 ◽

2021 ◽

pp. 2150323

Author(s):

Qing Gao ◽

Xuefeng Lu ◽

Xin Guo ◽

Junqiang Ren ◽

Hongtao Xue ◽

...

Keyword(s):

Yield Strength ◽

Deformation Mechanism ◽

Mechanical Performance ◽

Dislocation Motion ◽

Industrial Applications ◽

Shear Loading ◽

Dynamics Simulation ◽

Extraction Algorithm ◽

Micro Deformation ◽

And Control

Ni–Co alloy has great advantages in the fields of micro-electromechanical systems and aerospace, however, the lack of micro-deformation mechanism restricts its industrial application. Herein, the deformation mechanism and microstructure evolution of Ni–Co alloy nanoplate under shear loading are investigated by MD. The yield strength increases gradually with the increase of the velocity, and the highest shear modulus is 111.43 GPa. The stress concentration leads to the nucleation and expansion of the dislocation, and the stacking fault expands with the dislocation motion, swallowing most of the disordered atoms. By Dislocation Extraction Algorithm (DXA), it is found that Shockley and Perfect dislocations make a major role, and the interactions between dislocations are responsible for the high mechanical properties. As the temperature increases, the yield strength decreases significantly, the stress fluctuations in the plastic phase at 100 K and 200 K are greater compared to other temperatures. Meanwhile, the coherence of the dislocations motion decreases, and the atoms in the stacking faults are scattered, leading to the decreasing of area. The above results are helpful for the design and control of nanoelectronic facilities and provide a significant guide for the industrial applications of Ni–Co alloy nanoplate.

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Simulation of Deformation Behavior in Aluminum Alloys Having Bimodal Structures Based on the Theory of Crystal Plasticity Considering Dislocation Distributions

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.353-358.1102 ◽

2007 ◽

Vol 353-358 ◽

pp. 1102-1105

Author(s):

Yuji Nakasone ◽

Takeshi Yokoi ◽

Yasunao Sato

Keyword(s):

Yield Strength ◽

Size Effect ◽

Deformation Behavior ◽

Volume Fraction ◽

Tensile Deformation ◽

Polycrystalline Materials ◽

Bimodal Structure ◽

Polycrystal Plasticity ◽

Coarse Grains ◽

Proof Strength

The present paper describes the FEM code the present authors have developed based on the theory of the polycrystal plasticity with dislocation distributions taken into account and the simulations of tensile deformation behavior in FCC polycrystalline materials having bimodal structures by using the developed FEM code. In order to simulate the deformation behavior of materials having bimodal structures, it is necessary for the code to simulate the mesoscopic deformation behavior with the size effect of the initial yield strength, or the 0.2% proof strength. The present study has attempted to simulate the size effect of 0.2% proof strength by modifying the Bailey-Hirsch relation. By using the modified relation, the size effect of the initial plastic yield is successfully reproduced by FE polycrystal plasticity analysis. The results also showed that the 0.2% yield strength is decreased as the volume fraction of coarse grains is increased in the bimodal structure. As the ratio of the average diameter of fine grains to that of coarse grains is increased, the yield strength of the bimodal structure is decreased. The yield strength and work hardening rate of the bimodal structure, however, is not so much decreased as that of fine grain models. It was also revealed that the reason why materials having bimodal structures show higher ductility is that coarse grains yield in earlier stage of deformation and lower the maximum stress in the materials.

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The Mechanical Properties in the Vicinity of Grain Boundaries in Ultrafine-Grained and Polycrystalline Materials Studied by Nanoindentations

MRS Proceedings ◽

10.1557/proc-819-n4.9/p4.9 ◽

2004 ◽

Vol 819 ◽

Cited By ~ 2

Author(s):

E. Schweitzer ◽

K. Durst ◽

D. Amberger ◽

M. Göken

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Grain Boundaries ◽

Rate Sensitivity ◽

Dislocation Motion ◽

Polycrystalline Materials ◽

Petch Relation ◽

Angular Pressing ◽

Ultrafine Grained ◽

Second Phases

AbstractThe strength of structural materials strongly depends on the structure and properties of grain boundaries. Interfaces usually act as barriers to dislocation motion and therefore strengthen materials with decreasing grain size, quantitatively described by the well-known Hall-Petch relation. However, interfaces in nanocrystalline materials are often covered with impurities or second phases, which may influence the mechanical properties. With nanoindentation testing it is now possible to probe the strength of interfaces like grain boundaries directly on a nanometer scale. Therefore this method was used to investigate the properties in the vicinity of grain boundaries in polycrystalline materials with conventional grain size and in ultrafine-grained metals prepared by equal channel angular pressing (ECAP), where no impurities are introduced during processing. Measurements on an austenitic steel clearly show a decreasing hardness close to the interface opposite to the general expected behavior of strengthening. In this case segregation effects strongly influence the mechanical properties near the boundaries. The nanoindentation investigations on ultrafine-grained Al and Cu show a strong strain rate sensitivity. Inelastic effects are also found between unloading-loading segments during indentations.

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Microstructure and Formability of Different-Speeds Rolled AZ31 Mg Sheet

Materials Science Forum ◽

10.4028/www.scientific.net/msf.544-545.407 ◽

2007 ◽

Vol 544-545 ◽

pp. 407-410 ◽

Cited By ~ 3

Author(s):

Jae Seol Lee ◽

Hyeon Taek Son ◽

Young Kyun Kim ◽

Ik Hyun Oh ◽

Chang Seog Kang ◽

...

Keyword(s):

Mechanical Properties ◽

Tensile Strength ◽

Yield Strength ◽

Grain Boundary ◽

Microstructure Evolution ◽

Hot Rolling ◽

Potential Application ◽

Plastic Anisotropy ◽

Mg Alloys ◽

Az31 Mg Alloy

The aims of this study ares to investigate the microstructure evolution of AZ31 Mg alloys with normal rolling and different speeds rolling during hot rolling affects microstructure, texture and mechanical properties of AZ31 Mg alloy. In the microstructures of as-rolled both samples, twins are clearly apparent, small and recrystallized grains are visible along some grain boundary and twinned regions. The tensile strength and yield strength of DSR sample were slightly higher than that of NR sample. Also, in the case of the NR sample, tensile strength indicated different values to the rolling directions. From this result, NR sample compared to DSR sample strongly indicated to the plastic anisotropy tendency. Therefore, it is noted that DSR sample could be presented to the good formability, comparing to the NR sample. DSR samples deformed at 473K and 523K could be perfectly formed, indicating the potential application of the DSR process to improve formability of the Mg alloys at warm temperatures.

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