scholarly journals Dislocation Models for Strengthening in Nanostructured Metallic Multilayers

2000 ◽  
Vol 634 ◽  
Author(s):  
A. Misra ◽  
J. P. Hirth ◽  
H. Kung ◽  
R. G. Hoagland ◽  
J. D. Embury
Keyword(s):  
High Strength ◽  
Model Systems ◽  
Metallic Materials ◽  
Dislocation Loops ◽  
Metallic Multilayers ◽  
Dislocation Models ◽  
Dislocation Arrays ◽  
Pile Up ◽  
Model Predictions ◽  
Bilayer Period

ABSTRACTUltra-high strength metallic multilayers are ideal for investigating the effects of length scales in plastic deformation of metallic materials. Experiments on model systems show that the strengths of these materials increase with decreasing bilayer period following the Hall-Petch model. However, as the layer thickness is reduced to the nm-scale, the number of dislocations in the pile-up approaches one and the pile-up based Hall-Petch model ceases to apply. For nm-scale semi-coherent multilayers, we hypothesize that plastic flow occurs by the motion of single dislocation loops, initially in the softer layer, that deposit misfit type dislocation arrays at the interface and transfer load to the harder phase. The stress concentration eventually leads to slip in the harder phase, overcoming the resistance from the misfit arrays at the interface. A model is developed within the framework of classical dislocation theory to estimate the strengthening from this mechanism. The model predictions are compared with experimentally measured strengths.

Dislocation-Based Models of Stress-Strain Behavior in Multilayered Thin Films†

1997 ◽  
Vol 505 ◽  
Author(s):  
Peter M. Anderson ◽  
Eric R. Kreidler
Keyword(s):  
Thin Films ◽  
Critical Stress ◽  
Single Layer ◽  
Plastic Strains ◽  
Dislocation Loops ◽  
Strain Behavior ◽  
Dislocation Arrays ◽  
Pile Up ◽  
Softening Process ◽  
Multilayered Thin Films

ABSTRACTElementary dislocation arrays are applied to multilayered thin films to predict the critical stress required to propagate dislocation loops within individual layers and to study the tendency for deformation to be uniform or localized. The analyses suggest that shearing normal to layers is a mechanically unstable, softening process while stretching parallel to layers produces substantial hardening. Further, films with smaller layer thickness, h, require larger plastic strains to initiate pile-up modes of slip. Although the initial stress required to propagate an isolated loop within a single layer scales as ln(h)/h, there is a minimum h below which the critical stress is predicted to depend only on the resistance of the interface to dislocation transmission.

Anisotropy of Nanoindentation – a tool for the determination of nanocrystal orientation ?

2003 ◽  
Vol 779 ◽  
Author(s):  
David Christopher ◽  
Steven Kenny ◽  
Roger Smith ◽  
Asta Richter ◽  
Bodo Wolf ◽  
...  
Keyword(s):  
Crystal Surface ◽  
Scanning Force Microscopy ◽  
Depth Range ◽  
Dislocation Loops ◽  
Force Microscopy ◽  
Pile Up ◽  
Out Of Plane ◽  
Scanning Force ◽  
Dynamics Simulations

AbstractThe pile up patterns arising in nanoindentation are shown to be indicative of the sample crystal symmetry. To explain and interpret these patterns, complementary molecular dynamics simulations and experiments have been performed to determine the atomistic mechanisms of the nanoindentation process in single crystal Fe{110}. The simulations show that dislocation loops start from the tip and end on the crystal surface propagating outwards along the four in-plane <111> directions. These loops carry material away from the indenter and form bumps on the surface along these directions separated from the piled-up material around the indenter hole. Atoms also move in the two out-of-plane <111> directions causing propagation of subsurface defects and pile-up around the hole. This finding is confirmed by scanning force microscopy mapping of the imprint, the piling-up pattern proving a suitable indicator of the surface crystallography. Experimental force-depth curves over the depth range of a few nanometers do not appear smooth and show distinct pop-ins. On the sub-nanometer scale these pop-ins are also visible in the simulation curves and occur as a result of the initiation of the dislocation loops from the tip.

Analysis of Material Behaviour in Experimental and Simulative Setup of Joining by Forming of Aluminium Alloy and High Strength Steel with Shear-Clinching Technology

2014 ◽  
Vol 966-967 ◽  
pp. 549-556 ◽  
Author(s):  
Martin Müller ◽  
Réjane Hörhold ◽  
Marion Merklein ◽  
Gerson Meschut
Keyword(s):  
High Strength ◽  
Cost Effective ◽  
Metallic Materials ◽  
Material Behaviour ◽  
Transportation Sector ◽  
Reference Process ◽  
Key Factor ◽  
Mechanical Clinching ◽  
Safety Parameters ◽  
Systematic Development

In transportation sector the reduction of moving masses without the decrease of safety parameters is a key factor for future economic success. One possible approach for this is the use of different metallic materials in composite construction. Therefore, it is essential to establish a reliable component connection by means of suitable and cost-effective joining technologies. Mechanical joining technologies such as self-piercing riveting and mechanical clinching have proven to be effective methods for joining lightweight materials like aluminium and ductile steels. As these technologies require formability or pre-holing of the joining partners, the field of application is limited by the mechanical properties of the joining partners. Great potential for joining hot stamped steels, which have a very low elongation at fracture and therefore a low formability, offers the shear-clinching technology. For a systematic development of the shear-clinching technology, detailed investigations of the process are required. This paper presents an analysis of the material behaviour during the shear-clinching process and the reference process – clinching with pre-hole.

scholarly journals Ion Irradiation-Induced Microstructural Evolution of Ni–Mo–Cr Low Alloy Steels

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2268
Author(s):  
Hongying Sun ◽  
Penghui Lei ◽  
Guang Ran ◽  
Hui Wang ◽  
Jiyun Zheng ◽  
...  
Keyword(s):  
Irradiation Dose ◽  
Focused Ion Beam ◽  
Ion Irradiation ◽  
Ion Beam ◽  
High Strength ◽  
Positron Annihilation Spectroscopy ◽  
Small Scale ◽  
Low Alloy Steels ◽  
Dislocation Loops ◽  
S Parameter

As leading candidates of sheet steels for advanced nuclear reactors, three types of Ni–Mo–Cr high-strength low alloy (HSLA) steels named as CNST1, CNST2 and CNSS3 were irradiated by 400 keV Fe+ with peak fluence to 1.4 × 1014, 3.5 × 1014 and 7.0 × 1014 ions/cm2, respectively. The distribution and morphology of the defects induced by the sample preparation method and Fe+ irradiation dose were investigated by transmission electron microscopy (TEM) and positron-annihilation spectroscopy (PAS). TEM samples were prepared with two methods, i.e., a focused ion beam (FIB) technique and the electroplating and twin-jet electropolishing (ETE) method. Point defects and dislocation loops were observed in CNST1, CNST2 and CNSS3 samples prepared via FIB. On the other hand, samples prepared via the ETE method revealed that a smaller number of defects was observed in CNST1, CNST2 and almost no defects were observed in CNST3. It is indicated that artifact defects could be introduced by FIB preparation. The PAS S-W plots showed that the existence of two types of defects after ion implantation included small-scale defects such as vacancies, vacancy clusters, dislocation loops and large-sized defects. The S parameter of irradiated steels showed a clear saturation in PAS response with increasing Fe+ dose. At the same irradiation dose, higher values of the S-parameter were achieved in CNST1 and CNST2 samples when compared to that in CNSS3 samples. The mechanism and evolution behavior of irradiation-induced defects were analyzed and discussed.

scholarly journals Hierarchical nanostructured aluminum alloy with ultrahigh strength and large plasticity

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Ge Wu ◽  
Chang Liu ◽  
Ligang Sun ◽  
Qing Wang ◽  
Baoan Sun ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Structural Design ◽  
Flow Behavior ◽  
High Strength ◽  
Al Alloy ◽  
High Ductility ◽  
Metallic Materials ◽  
Trade Off ◽  
Ultrahigh Strength ◽  
Continuous Generation

Abstract High strength and high ductility are often mutually exclusive properties for structural metallic materials. This is particularly important for aluminum (Al)-based alloys which are widely commercially employed. Here, we introduce a hierarchical nanostructured Al alloy with a structure of Al nanograins surrounded by nano-sized metallic glass (MG) shells. It achieves an ultrahigh yield strength of 1.2 GPa in tension (1.7 GPa in compression) along with 15% plasticity in tension (over 70% in compression). The nano-sized MG phase facilitates such ultrahigh strength by impeding dislocation gliding from one nanograin to another, while continuous generation-movement-annihilation of dislocations in the Al nanograins and the flow behavior of the nano-sized MG phase result in increased plasticity. This plastic deformation mechanism is also an efficient way to decrease grain size to sub-10 nm size for low melting temperature metals like Al, making this structural design one solution to the strength-plasticity trade-off.

Phase Mixture Models for Metallic Materials with Submicrometer Grain Size

2003 ◽  
Vol 791 ◽  
Author(s):  
Yuri Estrin ◽  
Hyoung Seop Kim ◽  
Mark Bush
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Mixture Models ◽  
Cell Walls ◽  
Mechanical Response ◽  
Metallic Materials ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Model Predictions ◽  
Phase Mixture

ABSTRACTPhase mixture models describing the mechanical properties of submicrometer grained metals are presented. In this approach, grain boundaries or cell walls are treated as a separate phase. Two cases are considered: the mechanical response of an ultrafine grained material and the process of grain refinement by equal channel angular pressing. Model predictions with regard to the evolution of the microstructure, strength and texture are verified for Cu.

Influence of high-strength nanostructural states on properties of multifunctional metallic materials based on iron

2014 ◽  
Vol 5 (4) ◽  
pp. 364-371 ◽  
Author(s):  
V. V. Rusanenko ◽  
E. N. Blinova ◽  
V. P. Filippova ◽  
S. Yu. Makushev ◽  
O. P. Zhukov
Keyword(s):  
High Strength ◽  
Metallic Materials ◽  
Nanostructural States

A Review of Electrically-Assisted Manufacturing With Emphasis on Modeling and Understanding of the Electroplastic Effect

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Brandt J. Ruszkiewicz ◽  
Tyler Grimm ◽  
Ihab Ragai ◽  
Laine Mears ◽  
John T. Roth
Keyword(s):  
Fuel Economy ◽  
Elastic Recovery ◽  
Fuel Efficiency ◽  
High Strength ◽  
Carbon Steels ◽  
Metallic Materials ◽  
Low Carbon ◽  
Electroplastic Effect ◽  
Electrically Assisted ◽  
Electrically Assisted Manufacturing

Increasingly strict fuel efficiency standards have driven the aerospace and automotive industries to improve the fuel economy of their fleets. A key method for feasibly improving the fuel economy is by decreasing the weight, which requires the introduction of materials with high strength to weight ratios into airplane and vehicle designs. Many of these materials are not as formable or machinable as conventional low carbon steels, making production difficult when using traditional forming and machining strategies and capital. Electrical augmentation offers a potential solution to this dilemma through enhancing process capabilities and allowing for continued use of existing equipment. The use of electricity to aid in deformation of metallic materials is termed as electrically assisted manufacturing (EAM). The direct effect of electricity on the deformation of metallic materials is termed as electroplastic effect. This paper presents a summary of the current state-of-the-art in using electric current to augment existing manufacturing processes for processing of higher-strength materials. Advantages of this process include flow stress and forming force reduction, increased formability, decreased elastic recovery, fracture mode transformation from brittle to ductile, decreased overall process energy, and decreased cutting forces in machining. There is currently a lack of agreement as to the underlying mechanisms of the electroplastic effect. Therefore, this paper presents the four main existing theories and the experimental understanding of these theories, along with modeling approaches for understanding and predicting the electroplastic effect.

The Influence of Amorphizing Implants on Boron Diffusion in Silicon

1997 ◽  
Vol 469 ◽  
Author(s):  
H. S. Chao ◽  
P. B. Griffin ◽  
J. D. Plummer
Keyword(s):  
Point Defects ◽  
Field Enhancement ◽  
Enhancement Effect ◽  
Dislocation Loops ◽  
Boron Diffusion ◽  
Electric Field Enhancement ◽  
Diffusion Behavior ◽  
Enhanced Diffusion ◽  
Pile Up ◽  
Experimental Structure

ABSTRACTThe transient enhanced diffusion behavior of B after ion implantation above the amorphization threshold is investigated. The experimental structure uses a layer of epitaxially grown Si, uniformly doped with B to act as a diffusion monitor. Wafers using this structure are implanted with amorphizing doses of Si, As, or P and annealed for various times at various temperatures. The experimental results show that upon annealing after Si implantation, there is a large amount of B pile-up that occurs at the amorphous/crystalline (A/C) interface while B is depleted from the region just beyond the A/C interface. This pile-up/depletion phenomenon can be attributed to the dislocation loops that form at the A/C interface. These loops act as sinks for interstitial point defects. There is also B pile-up/depletion behavior for As and P implants as well. However, this behavior may be explained by an electric field enhancement effect. While dislocation loops are known to form at the A/C interface for all of the investigated implant conditions, it appears that while they are necessary to simulate for Si amorphizing implants, they may not be necessary to simulate for As and P amorphizing implants.

Changes in the dislocation arrays of high-strength structural steel during fatigue

1974 ◽  
Vol 16 (2) ◽  
pp. 144-146
Author(s):  
V. I. Bol'shakov ◽  
V. S. Zoteev ◽  
L. G. Orlov ◽  
M. A. Tylkin
Keyword(s):  
Structural Steel ◽  
High Strength ◽  
Dislocation Arrays
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