Molecular Dynamic Computer Simulation of Elastic and Plastic Behavior of Nanophase Ni

1996 ◽  
Vol 457 ◽  
Author(s):  
H. Van Swygenhoven ◽  
A. Caro
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Grain Boundary ◽  
Young Modulus ◽  
Grain Boundary Sliding ◽  
Plastic Behavior ◽  
Grain Rotation ◽  
Mean Grain Size ◽  
Dynamic Computer Simulation ◽  
Elastic And Plastic Deformation

ABSTRACTMolecular dynamics computer simulations of low temperature elastic and plastic deformation of Ni nanophase samples with several mean grain size in the range 3–5 nm are reported. The samples are polycrystals nucleated from different seeds, with random locations and orientations. Bulk and Young modulus are calculated from stress-strain curves and the onsett of plastic deformation is discussed. At higher loads substantial difference in the plastic behaviour with respect to the coarse grain counterpart is observed: among the mechanism responsible for the deformation, grain boundary sliding and motion, as well as grain rotation are identified. An interpretation in terms of grain boundary viscosity is proposed and a linear dependence of strain rate with the inverse of the grain size is obtained.

scholarly journals Molecular Dynamics as a Means to Investigate Grain Size and Strain Rate Effect on Plastic Deformation of 316 L Nanocrystalline Stainless-Steel

Materials ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3223 ◽  
Author(s):  
Abdelrahim Husain ◽  
Peiqing La ◽  
Yue Hongzheng ◽  
Sheng Jie
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Stainless Steel ◽  
Grain Boundary ◽  
Strain Rate ◽  
Deformation Mechanism ◽  
Grain Boundary Sliding ◽  
Plastic Deformation Mechanism ◽  
Grain Sizes ◽  
Critical Grain Size

In the present study, molecular dynamics simulations were employed to investigate the effect of strain rate on the plastic deformation mechanism of nanocrystalline 316 L stainless-steel, wherein there was an average grain of 2.5–11.5 nm at room temperature. The results showed that the critical grain size was 7.7 nm. Below critical grain size, grain boundary activation was dominant (i.e., grain boundary sliding and grain rotation). Above critical grain size, dislocation activities were dominant. There was a slight effect that occurred during the plastic deformation mechanism transition from dislocation-based plasticity to grain boundaries, as a result of the stress rate on larger grain sizes. There was also a greater sensitive on the strain rate for smaller grain sizes than the larger grain sizes. We chose samples of 316 L nanocrystalline stainless-steel with mean grain sizes of 2.5, 4.1, and 9.9 nm. The values of strain rate sensitivity were 0.19, 0.22, and 0.14, respectively. These values indicated that small grain sizes in the plastic deformation mechanism, such as grain boundary sliding and grain boundary rotation, were sensitive to strain rates bigger than those of the larger grain sizes. We found that the stacking fault was formed by partial dislocation in all samples. These stacking faults were obstacles to partial dislocation emission in more sensitive stress rates. Additionally, the results showed that mechanical properties such as yield stress and flow stress increased by increasing the strain rate.

scholarly journals Grain Rotation in Plastic Deformation

2019 ◽  
Vol 3 (3) ◽  
pp. 17 ◽  
Author(s):  
Bin Chen ◽  
Linli Zhu ◽  
Yunchang Xin ◽  
Jialin Lei
Keyword(s):  
Plastic Deformation ◽  
Grain Boundary ◽  
Materials Science ◽  
Theoretical Models ◽  
Grain Boundary Sliding ◽  
Experimental Investigations ◽  
Characterization Methods ◽  
Grain Rotation ◽  
X Ray ◽  
Dynamics Simulations

The plastic deformation behaviors of crystalline materials are usually determined by lattice dislocations. However, below a certain particle or grain size, focus is placed on the grain-boundary-mediated mechanisms (e.g., grain rotation, grain boundary sliding, and diffusion), which has been observed during recrystallization, grain growth, and plastic deformation. However, the underlying mechanisms of grain rotation remain to be studied. In this article, we review the theoretical models, molecular dynamics simulations, and experimental investigations on grain rotation. Especially, the development of in situ transmission electron microscopy (TEM) and X-ray characterization methods for probing grain boundary processes during plastic deformation provides a better understanding of the mechanisms of grain rotation. Moreover, the ability to acquire high-quality X-ray diffraction patterns from individual nanograins is expected to find broad applications in various fields such as physics, chemistry, materials science, physics, and nanoscience.

The Effect of Grain Boundary State on Deformation Process Development in Nanostructured Metals Produced by the Methods of Severe Plastic Deformation

2011 ◽  
Vol 683 ◽  
pp. 69-79 ◽  
Author(s):  
Evgeny V. Naydenkin ◽  
Galina P. Grabovetskaya ◽  
Konstantin Ivanov
Keyword(s):  
Plastic Deformation ◽  
Grain Boundary ◽  
Severe Plastic Deformation ◽  
Deformation Process ◽  
Process Development ◽  
Grain Boundary Sliding ◽  
Total Deformation ◽  
Nanostructured Metals ◽  
Boundary State ◽  
Boundary Sliding

In this review the investigations of deformation process development are discussed which were carried out by tension and creep in the temperature range Т<0.4Tm (here Тm is the absolute melting point of material) for nanostructured metals produced by the methods of severe plastic deformation. The contribution of grain boundary sliding to the total deformation in the above temperature interval is also considered. An analysis is made of the effect of grain size and grain boundary state on the evolution of grain boundary sliding and cooperative grain boundary sliding in nanostructured metals.

scholarly journals The role of grain size evolution in the rheology of ice: implications for reconciling laboratory creep data and the Glen flow law

2021 ◽  
Vol 15 (9) ◽  
pp. 4589-4605
Author(s):  
Mark D. Behn ◽  
David L. Goldsby ◽  
Greg Hirth
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Stress Exponent ◽  
Ice Sheets ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Ice Flow ◽  
Size Evolution ◽  
Boundary Sliding ◽  
Flow Law

Abstract. Viscous flow in ice is often described by the Glen flow law – a non-Newtonian, power-law relationship between stress and strain rate with a stress exponent n ∼ 3. The Glen law is attributed to grain-size-insensitive dislocation creep; however, laboratory and field studies demonstrate that deformation in ice can be strongly dependent on grain size. This has led to the hypothesis that at sufficiently low stresses, ice flow is controlled by grain boundary sliding, which explicitly incorporates the grain size dependence of ice rheology. Experimental studies find that neither dislocation creep (n ∼ 4) nor grain boundary sliding (n ∼ 1.8) have stress exponents that match the value of n ∼ 3 in the Glen law. Thus, although the Glen law provides an approximate description of ice flow in glaciers and ice sheets, its functional form is not explained by a single deformation mechanism. Here we seek to understand the origin of the n ∼ 3 dependence of the Glen law by using the “wattmeter” to model grain size evolution in ice. The wattmeter posits that grain size is controlled by a balance between the mechanical work required for grain growth and dynamic grain size reduction. Using the wattmeter, we calculate grain size evolution in two end-member cases: (1) a 1-D shear zone and (2) as a function of depth within an ice sheet. Calculated grain sizes match both laboratory data and ice core observations for the interior of ice sheets. Finally, we show that variations in grain size with deformation conditions result in an effective stress exponent intermediate between grain boundary sliding and dislocation creep, which is consistent with a value of n = 3 ± 0.5 over the range of strain rates found in most natural systems.

Superplasticity of Mg-Zn-Y Alloy Prepared by Extrusion of Machined Chip

2012 ◽  
Vol 735 ◽  
pp. 259-264
Author(s):  
Takaomi Itoi ◽  
Syuichi Fudetani ◽  
Mitsuji Hirohashi
Keyword(s):  
Grain Size ◽  
Hot Extrusion ◽  
Initial Strain Rate ◽  
Grain Boundary Sliding ◽  
Initial Strain ◽  
Strain Rates ◽  
Long Period ◽  
Dominant Deformation Mechanism ◽  
Mean Grain Size ◽  
Boundary Sliding

Mg96Zn2Y2 (at.%) extruded alloy was fabricated by hot-extrusion of the Mg96Zn2Y2 machined chip. The Mg96Zn2Y2 extruded alloy consisted of a long period stacking ordered (LPSO)-, Mg3Zn3Y2- and Mg- phases. The Mg phase with mean grain size of 450 nm was confirmed by TEM. However, the LPSO- and Mg3Zn3Y2- phases had relatively large grain size compared with Mg phase. The Mg96Zn2Y2 extruded alloy also showed superplasticity at temperatures of 623 K and 723 K with initial strain rates from 2×10−1 s−1 to 2×10−3 s−1. The maximum elongation of 450 % was achieved at 723 K with an initial strain rate of 2×10−3 s−1. From TEM observation, it is considered that grain boundary sliding of Mg grains was dominant deformation mechanism of the Mg96Zn2Y2 extruded alloy at high temperature range.

Mechanical Properties of Novel Nanocrystalline Materials

2001 ◽  
Author(s):  
J. Narayan ◽  
H. Wang ◽  
A. Kvit
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Nanocrystalline Materials ◽  
High Surface ◽  
Grain Boundary Sliding ◽  
Boundary Shear ◽  
Functionally Gradient ◽  
Boundary Sliding ◽  
First Time ◽  
Critical Grain Size

Abstract We have synthesized nanocrystalline thin films of Cu, Zn, TiN, and WC having uniform grain size in the range of 5 to 100 nm. This was accomplished by introducing a couple of manolayers of materials with high surface and have a weak interaction with the substrate. The hardness measurements of these well-characterized specimens with controlled microstructures show that hardness initially increases with decreasing grain size following the well-known Hall-Petch relationship (H∝d−½). However, there is a critical grain size below which the hardness decreases with decreasing grain size. The experimental evidence for this softening of nanocrystalline materials at very small grain sizes (referred as reverse Hall-Petch effect) is presented for the first time. Most of the plastic deformation in our model is envisioned to be due to a large number of small “sliding events” associated with grain boundary shear or grain boundary sliding. This grain-size dependence of hardness can be used to create functionally gradient materials for improved adhesion and wear among other improved properties.

Mechanical Behaviour of Nanocrystalline Copper Related to Grain-boundary Structure

2002 ◽  
Vol 727 ◽  
Author(s):  
Y. Champion ◽  
P. Langlois ◽  
S. Guérin-Mailly ◽  
C. Langlois ◽  
M. J. Hÿtch
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Structural Analysis ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Mechanical Behaviour ◽  
Tensile Testing ◽  
Metallic Nanostructures ◽  
Nanocrystalline Powders ◽  
Clear Understanding

AbstractUnderstanding the mechanical behaviour of metallic nanostructures is a key issue for their development. On the one hand, knowledge of the plastic behaviour at various temperatures is essential to control the synthesis, forming, and machining of such materials. Equally, a clear understanding of atomic and mesoscopic mechanisms, involving defects and their interactions, is essential for the control of ageing and functional properties. Regarding plastic deformation at room temperature, there is now evidence for unusual behaviour in nanostructured metals. In addition to high resistance and ductility, tensile testing reveals peculiar elasto-plastic deformation. Such behaviour was initially attributed to grain-boundary sliding. However, intergranular areas (including triple junctions) may possess special properties compared to their microcrystalline counterparts. For example, low activation energies have been measured for grain-boundary diffusion and it has been observed that grain-boundaries may act as dislocation sources and nucleation sites for deformation twinning.In this paper, we report on analysis on bulk copper nanostructures. Grain-boundaries are studied, by cross-correlating information from mechanical tensile testing and structural analysis, including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Macroscopic bulk specimens (with grain size of about 80 nm) are prepared by powder metallurgy techniques, modified to fit to the special properties of nanocrystalline powders. Processing includes coldisostatic pressing, sintering and differential extrusion. The powders used (grain size of 40 nm) are synthesised by evaporation and cryo-condensation of a metallic vapour within liquid nitrogen. Results on mechanical testing and structural analysis will be reported. Emphasis will be placed on the structure of grain-boundaries (type of grain-boundary, grain-boundary thickness) studied by TEM and high resolution TEM image analysed using the geometric phase technique. The nanostructure was revealed to be consist in agglomerate of nano-size grains separated by low angle grain-boundaries. Agglomerates are themselves separerated by general high angle boundaries. These observations will then be related to the unusual mechanical true stress-true strain curves of the metallic nanostructures.

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