scholarly journals Structure and Mechanical Behavior of Bulk Nanocrystalline Materials

MRS Bulletin ◽  
1999 ◽  
Vol 24 (2) ◽  
pp. 44-53 ◽  
Author(s):  
J.R. Weertman ◽  
D. Farkas ◽  
K. Hemker ◽  
H. Kung ◽  
M. Mayo ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Grain Size ◽  
Mechanical Behavior ◽  
Nanocrystalline Materials ◽  
Volume Fraction ◽  
Grain Boundary Sliding ◽  
Uniaxial Tensile ◽  
Fine Grained ◽  
Grain Sizes

The reduction of grain size to the nanometer range (˜2-100 nm) has led to many interesting materials properties, including those involving mechanical behavior. In the case of metals, the Hall-Petch equation, which relates the yield stress to the inverse square root of the grain size, predicts great increases in strength with grain refinement. On the other hand, theory indicates that the high volume fraction of interfacial regions leads to increased deformation by grain-boundary sliding in metals with grain size in the low end of the nanocrystalline range. Nanocrystalline ceramics also have desirable properties. Chief among these are lower sintering temperatures and enhanced strain to failure. These two properties acting in combination allow for some unique applications, such as low-temperature diffusion bonding (the direct joining of ceramics to each other using moderate temperatures and pressures). Mechanical properties sometimes are affected by the fact that ceramics in a fine-grained form are stable in a different (usually higher pressure) phase than that which is considered “normal” for the ceramic. To the extent that the mechanical properties of a ceramic are dependent on its crystal-lographic structure, these differences will become evident at the smaller size scales.It is uncertain how deformation takes place in very fine-grained nanocrystalline materials. It has been recognized for some time that the Hall-Petch relationship, which usually is explained on the basis of dislocation pileups at grain boundaries, must break down at grain sizes such that a grain cannot support a pileup. Even some of the basic assumptions of dislocation theory may no longer be appropriate in this size regime. Recently considerable progress has been made in simulating the behavior of extremely fine-grained metals under stress using molecular-dynamics techniques. Molecular-dynamics (MD) simulations of deformation in nanophase Ni and Cu were carried out in the temperature range of 300–500 K, at constant applied uniaxial tensile stresses between 0.05 GPa and 1.5 GPa, on samples with average grain sizes ranging from 3.4 nm to 12 nm.

scholarly journals Is Superplasticity in the Future of Nanophase Materials?

1990 ◽  
Vol 196 ◽  
Author(s):  
R. W. Siegel
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Room Temperature ◽  
Grain Boundary Sliding ◽  
Atomic Clusters ◽  
Diffusional Creep ◽  
Ultrafine Grain ◽  
Grain Sizes ◽  
Nanophase Materials ◽  
Boundary Sliding

ABSTRACTThe ultrafine grain sizes and high diffusivities in nanophase materials assembled from atomic clusters suggest that these materials may have a strong tendency toward superplastic mechanical behavior. Both small grain size and enhanced diffusivity can be expected to lead to increased diffusional creep rates as well as to a significantly greater propensity for grain boundary sliding. Recent mechanical properties measurements at room temperature on nanophase Cu, Pd, and TiO2, however, give no indications of superplasticity. Nonetheless, significant ductility has been clearly demonstrated in these studies of both nanophase ceramics and metals. The synthesis of cluster-assembled nanophase materials is described and the salient features of what is known of their structure and mechanical properties is reviewed. Finally, the answer to the question posed in the title is addressed.

Characterization of Defect Nucleation and Propagation in Fe2O3+FCC-Al Nanocomposites During Uniaxial Tensile and Compressive Deformations

2006 ◽  
Author(s):  
Vikas Tomar ◽  
Min Zhou
Keyword(s):  
Molecular Dynamics ◽  
Grain Size ◽  
Defect Formation ◽  
Voronoi Tessellation ◽  
Orientation Distribution ◽  
Uniaxial Tensile ◽  
Grain Sizes ◽  
Classical Molecular Dynamics ◽  
Average Grain Size ◽  
Nanocrystalline Structures

The objective of this research is to analyze uniaxial tensile and compressive mechanical deformations of α-Fe2O3 + fcc Al nanoceramic-metal composites using classical molecular dynamics (MD). Specifically, variations in the nucleation and the propagation of defects (such as dislocations and stacking faults etc.) with variation in the nanocomposite phase morphology and their effect on observed tensile and compressive strengths of the nanocomposites are analyzed. For this purpose, a classical molecular dynamics (MD) potential that includes an embedded atom method (EAM) cluster functional, a Morse type pair function, and a second order electrostatic interaction function is developed, see Tomar and Zhou (2004) and Tomar and Zhou (2006b). The nanocrystalline structures (nanocrystalline Al, nanocrystalline Fe2O3 and the nanocomposites with 40% and 60% Al by volume) with average grain sizes of 3.9 nm, 4.7 nm, and 7.2 nm are generated using a combination of the well established Voronoi tessellation method with the Inverse Monte-Carlo method to conform to prescribed log-normal grain size distributions. For comparison purposes, nanocrystalline structures with a specific average grain size have the same grain morphologies and the same grain orientation distribution. MD simulations are performed at the room temperature (300 K). Calculations show that the deformation mechanism is affected by a combination of factors including the fraction of grain boundary (GB) atoms and the electrostatic forces between atoms. The significance of each factor is dependent on the volume fractions of the Al and Fe2O3 phases. Depending on the relative orientations of the two phases at an interface, the contribution of the interface to the defect formation varies. The interfaces have stronger effect in structures with smaller average grain sizes than in structures with larger average grain sizes.

Effect of Grain Size on Mechanical Properties of Dual Phase Steels Composed of Ferrite and Martensite

MRS Advances ◽  
2016 ◽  
Vol 1 (12) ◽  
pp. 811-816 ◽  
Author(s):  
Myeong-heom Park ◽  
Akinobu Shibata ◽  
Nobuhiro Tsuji
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Grain Size ◽  
Tensile Test ◽  
Coarse Grained ◽  
Dual Phase ◽  
Fine Grained ◽  
Grain Sizes ◽  
Dp Structure ◽  
Dp Steels

ABSTRACTIt is well-known that dual phase (DP) steels composed of ferrite and martensite have good ductility and plasticity as well as high strength. Due to their excellent mechanical properties, DP steels are widely used in the industrial field. The mechanical properties of DP steels strongly depend on several factors such as fraction, distribution and grain size of each phase. In this study, the grain size effect on mechanical properties of DP steels was investigated. In order to obtain DP structures with different grain sizes, intercritical heat treatment in ferrite + austenite two-phase region was carried out for ferrite-pearlite structures having coarse and fine ferrite grain sizes. These ferrite-pearlite structures with coarse and fine grains were fabricated by two types of heat treatments; austenitizing heat treatment and repetitive heat treatment. Ferrite grain sizes of the specimens heat-treated by austenitizing and repetitive heat treatment were 47.5 µm (coarse grain) and 4.5 µm (fine grain), respectively. The ferrite grain sizes in the final DP structures fabricated from the coarse-grained and fine-grained ferrite-pearlite structures were 58.3 µm and 4.1µm, respectively. The mechanical behavior of the DP structures with different grain sizes was evaluated by an uniaxial tensile test at room temperature. The local strain distribution in the specimens during tensile test was obtained by a digital image correlation (DIC) technique. Results of the tensile test showed that the fine-grained DP structure had higher strength and larger elongation than the coarse-grained DP structure. It was found by the DIC analysis that the fine-grained DP structure showed homogeneous deformation compared with the coarse-grained DP structure.

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

2019 ◽  
Vol 55 (7) ◽  
pp. 2661-2681 ◽  
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.

Grain-size dependence of mechanical properties in polycrystalline boron-nitride: a computational study

2015 ◽  
Vol 17 (34) ◽  
pp. 21894-21901 ◽  
Author(s):  
Matthew Becton ◽  
Xianqiao Wang
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Grain Size ◽  
Boron Nitride ◽  
Molecular Dynamics Simulations ◽  
Failure Mechanism ◽  
Size Dependence ◽  
Computational Study ◽  
Grain Sizes ◽  
Dynamics Simulations

Molecular dynamics simulations are performed to investigate the mechanical properties and failure mechanism of polycrystalline boron nitride sheet with various grain sizes.

scholarly journals Influence of Temperature on Mechanical Properties of Nanocrystalline 316L Stainless Steel Investigated via Molecular Dynamics Simulations

Materials ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 2803 ◽  
Author(s):  
Abdelrahim Husain ◽  
Peiqing La ◽  
Yue Hongzheng ◽  
Sheng Jie
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Grain Size ◽  
Stainless Steel ◽  
Molecular Dynamics Simulations ◽  
Yield Stress ◽  
316L Stainless Steel ◽  
Deformation Mechanisms ◽  
Grain Sizes ◽  
Dynamics Simulations

Molecular dynamics simulations were conducted to study the mechanical properties of nanocrystalline 316L stainless steel under tensile load. The results revealed that the Young’s modulus increased with increasing grain size below the critical average grain size. Two grain size regions were identified in the plot of yield stress. In the first region, corresponding to grain sizes above 7.7 nm, the yield stress decreased with increasing grain size and the dominant deformation mechanisms were deformation twinning and extended dislocation. In the second region, corresponding to grain sizes below 7.7 nm, the yield stress decreased rapidly with decreasing grain size and the dominant deformation mechanisms were grain boundary sliding and also grain rotation. The yield strength and Young’s modulus were both found to decrease with increasing temperature, which increased the interatomic distance and thereby decreased the interatomic bonding force.

scholarly journals Prediction of mechanical properties of nanocrystalline materials using Voronoi FE models of representative volume elements

2018 ◽  
Vol 233 ◽  
pp. 00029
Author(s):  
Panagiotis Bazios ◽  
Konstantinos Tserpes ◽  
Spiros Pantelakis
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Volume Fraction ◽  
Voronoi Tessellation ◽  
Numerical Results ◽  
Element Analysis ◽  
Representative Volume ◽  
Representative Volume Elements

In the present work, a numerical model is developed to predict the mechanical properties of nanocrystalline materials using a Finite Element Analysis. The model is based on Representative Volume Elements (RVE) in which the microstructure of the material is described using the Voronoi tessellation algorithm. The use of the Voronoi particles was based on the observation of the morphology of nanocrystalline materials by Scanning Electron and Transmission Electron Microscopy. In each RVE, three-dimensional modelling of the grain and grain boundaries as randomlyshaped sub-volumes is performed. The developed model has been applied to pure nanocrystallline copper taking into account the parameters of grain size and grain boundary thickness. The mechanical properties of nanocrystalline copper have been computed by loading the RVE in tension. The numerical results gave a clear evidence of grain size effect and the Hall-Petch relationship, which is a consequence of macroscopic strain being preferentially accumulated at grain boundaries. On the other hand, for a given grain volume fraction, the results for elastic moduli showed no effect of the grain size. The model predictions have been validated successfully against numerical results from the literature and predictions of the Rule of Mixtures and the Mori-Tanaka analytical model.

Effect of Grain Size and Grain Boundary on Mechanical Yielding Behavior of Fully Stabilized Zirconia

2006 ◽  
Author(s):  
Jie Lian ◽  
Javier Garay ◽  
Junlan Wang
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Grain Boundary ◽  
Boundary Effect ◽  
Coarse Grained ◽  
Stabilized Zirconia ◽  
Fine Grained ◽  
Grain Sizes ◽  
Reduced Modulus ◽  
Grain Boundary Effect

Mechanical properties of fully yttria stabilized zirconia (F-YSZ) with different grain sizes were investigated using instrumented indentation. While the grain size effect on the yield strength was performed on both the coarse-grained and fine-grained F-YSZ, the grain boundary effect was studied on the coarse-grained F-YSZ by performing nanoindentation within the grains and on/near the grain boundaries. Little variations were observed on mechanical properties such as hardness and reduced modulus, interesting results were obtained on the grain boundary effect on the yielding load for the course-grained F-YSZ.

Nanograin size effects on deformation mechanisms and mechanical properties of nickel: A molecular dynamics study

2021 ◽  
Vol 11 (11) ◽  
pp. 1841-1855
Author(s):  
Alexandre Melhorance Barboza ◽  
Ivan Napoleão Bastos ◽  
Luis César Rodríguez Aliaga
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Grain Size ◽  
Stress Relaxation ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Rate Sensitivity ◽  
Deformation Mechanisms ◽  
Triple Junctions ◽  
Grain Sizes

The grain size refinement of metallic materials to the nanometer scale produces interesting properties compared to the coarse-grained counterparts. Their mechanical behavior, however, cannot be explained by the classical deformation mechanisms. Using molecular dynamics simulations, the present work examines the influence of grain size on the deformation mechanisms and mechanical properties of nanocrystalline nickel. Samples with grain sizes from 3.2 to 24.1 nm were created using the Voronoi tessellation method and simulated in tensile and relaxation tests. The yield and ultimate tensile stresses follow an inverse Hall-Petch relationship for grain sizes below ca. 20 nm. For samples within the conventional Hall-Petch regime, no perfect dislocations were observed. Nonetheless, a few extended dislocations were nucleated from triple junctions, suggesting that the suppression of conventional slip mechanism is not uniquely responsible for the inverse Hall-Petch behavior. For samples respecting the inverse Hall-Petch regime, the high number of triple junctions and grain boundaries allowed grain rotation, grain boundary sliding, and diffusion-like behavior that act as competitive deformation mechanisms. For all samples, the atomic configuration analysis showed that Shockley partial dislocations are nucleated at grain boundaries, crossing the grain before being absorbed in opposite grain boundaries, leaving behind stacking faults. Interestingly, the stress relaxation tests showed that the strain rate sensitivity decreases with grain size for a specific grain size range, whereas for grains below approximately 10 nm, the strain rate sensitivity increases as observed experimentally. Repeated stress relaxation tests were also performed to obtain the effective activation volume parameter. However, the expected linear trend in pertinent plots required to obtain this parameter was not found.

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