Estimation of Dislocation Concentration in Plastically Deformed FeCrNi Alloy by Positron Annihilation Lifetime

2017 ◽  
Vol 373 ◽  
pp. 162-166
Author(s):  
Er Yang Lu ◽  
Xing Zhong Cao ◽  
Shuo Xue Jin ◽  
Yi Hao Gong ◽  
Peng Zhang ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Point Defects ◽  
Trapping Efficiency ◽  
Model Alloy ◽  
Positron Annihilation Lifetime ◽  
Pile Up ◽  
Cold Rolled ◽  
The Mean ◽  
Positron Lifetimes ◽  
Trapping Sites

Dislocations would be induced after plastic deformation, which might change the mechanical properties of solids. FeCrNi austenitic model alloy and its Mo-diluted alloy were cold rolled with different degree of thickness reduction. Positrons are sensitive to point defects, which are easily trapped and annihilated around the trapping sites. The mean positron lifetimes have been used to estimate the average dislocation concentration in solids. Meanwhile, the trapping efficiency μ was calculated from the lifetime results. The trapping efficiency value is estimated about 3.31×10-7 cm3s-1 for FeCrNi alloy and 3.31×10-7 cm3s-1 for Mo-diluted alloy, respectively. The increment of the hardness value during plastic deformation is related to the increase of the dislocation density and dislocation pile up in solids.

Modelling of Recrystallization Nucleation at Hard Inclusions

2012 ◽  
Vol 715-716 ◽  
pp. 593-598
Author(s):  
Werner Mitter ◽  
Christof Sommitsch
Keyword(s):  
Plastic Deformation ◽  
Dislocation Density ◽  
Point Defects ◽  
Strain Energy ◽  
Metallic Structure ◽  
Pile Up ◽  
High Gradients ◽  
Diffusional Flow ◽  
Edge Dislocations

During plastic deformation, a metallic structure is deformed inhomogeneously near hard inclusions. Hence both the materials strengthening and recovery and thus softening depends on the local position. There are thus high gradients of point defects, such as vacancies and interstitials, of the dislocation density and hence of the strain energy. Those gradients govern the diffusional flow, whose pile-up influences the climbing of edge dislocations, i.e. recovery and materials softening, respectively.

Determination of the activation enthalpy for migration of dislocations in plastically deformed 8006 Al-alloy by positron annihilation lifetime technique

2016 ◽  
Vol 30 (18) ◽  
pp. 1650110 ◽  
Author(s):  
Mohammed Salah ◽  
M. Abdel-Rahman ◽  
Emad A. Badawi ◽  
M. A. Abdel-Rahman
Keyword(s):  
Plastic Deformation ◽  
Positron Annihilation ◽  
Point Defects ◽  
Isothermal Annealing ◽  
Activation Enthalpy ◽  
Hydraulic Press ◽  
Al Alloy ◽  
Slow Cooling ◽  
Positron Annihilation Lifetime

The activation enthalpy for migration of dislocations of plastically deformed 8006 Al-alloy was investigated by positron annihilation lifetime technique. Plastic deformation using a hydraulic press produces mainly dislocations and may produce point defects. The type of defect was studied by isochronal annealing which determines the temperature range of recovery of each type. Only one type of defect (dislocations) was observed for the investigated sample and was found to be recovered within the range 455–700 K. Isothermal annealing by slow cooling was performed through this range and used in determination of the activation enthalpy of migration of dislocations which was found to be 0.26 ± 0.01 eV.

Microstructure and Texture Evolution in a Cold-Rolled High Mn Steel with Microadditions of Ti and Nb

2013 ◽  
Vol 203-204 ◽  
pp. 71-76
Author(s):  
Sławomir Kołodziej ◽  
Joanna Kowalska ◽  
Wiktoria Ratuszek ◽  
Wojciech Ozgowicz ◽  
Krzysztof Chruściel
Keyword(s):  
Plastic Deformation ◽  
Texture Evolution ◽  
Hexagonal Structure ◽  
Cold Plastic Deformation ◽  
Α Phase ◽  
Ε Phase ◽  
Cold Rolled ◽  
Goss Orientation ◽  
Mn Steel ◽  
Microscopic Investigations

The aim of this work was the microstructure and texture analysis of a deformed via cold-rolling 24.5Mn-3.5Si-1.5Al-Ti-Nb TWIP/TRIP type steel. It was found, that during cold plastic deformation a phase transformation of austenite into martensite takes place. The transformation progress was confirmed by the microscopic investigations. The texture of austenite is characterized by a limited α1=||RD fibre and the γ=||ND fibre. The texture of austenite changed with increasing deformation rate. In the texture of deformed austenite the strongest orientation is the {110} Goss orientation, which belongs to the α=||ND orientation fibre. During cold plastic deformation γ→ε and γ→ε→α’ phase transformations as well as the deformation of γ, ε and α’ phases are taking place in the steel. The formed ε phase (hexagonal structure) also possesses a distinct texture.

The Behavior of Long Beams Under Impact Loading

1950 ◽  
Vol 17 (1) ◽  
pp. 27-34
Author(s):  
P. E. Duwez ◽  
D. S. Clark ◽  
H. F. Bohnenblust
Keyword(s):  
Plastic Deformation ◽  
Cross Sections ◽  
Constant Velocity ◽  
Bending Moment ◽  
Infinite Length ◽  
Longitudinal Impact ◽  
Deflection Curve ◽  
Transverse Impact ◽  
Cold Rolled ◽  
Annealed Copper

Abstract This paper presents the results of a theoretical and experimental investigation of the plastic deformation of long beams which are subjected to a concentrated transverse impact of constant velocity. In the theoretical analysis, the beam is supposed to be of infinite length, and plane cross sections are assumed to remain plane. The bending moment is assumed to depend on the curvature according to a function that is obtained from the stress-strain curve of the material. The theory neglects both the lateral displacement of the cross sections against each other due to the shearing force and the rotary kinetic energy of the motion of the beam. The theory shows that a strain is not propagated along a beam at constant velocity, as in the case of longitudinal impact. The strain depends on the ratio between the square of the distance from the point of impact and the time. This is correct regardless of the shape of the moment - curvature curve. If certain approximations are applied to the bending moment - curvature curve, the theory provides a method of computing the deflection curve of a beam at any instant during impact. An experimental study has been made in which the deflection curves of long simply supported beams have been obtained during impact. The deflection characteristics of a cold-rolled steel and an annealed-copper beam have been computed by approximating the bending moment - curvature curves. It is shown that for materials such as cold-rolled low-carbon steel, for which plastic deflection is localized at the point of impact, the observed deflection curve is closely approximated by computing a curve based on the assumption that the beam remains elastic. For a soft material like annealed copper, plastic deformation extends over a relatively large distance from the point of impact and, taking plastic deformation into account, a satisfactory agreement is obtained between theory and experimental results.

Effect of Strain Amounts on Cold Compression Deformation Mechanism of Ti-55531 Alloy with Bimodal Microstructure

2021 ◽  
Vol 1035 ◽  
pp. 182-188
Author(s):  
Jian Hua Cai ◽  
She Wei Xin ◽  
Lei Li ◽  
Lei Zou ◽  
Hai Ying Yang ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Deformation Mechanism ◽  
True Strain ◽  
Bimodal Microstructure ◽  
Free Zone ◽  
Β Phase ◽  
Α Phase ◽  
Initial Stage ◽  
Pile Up ◽  
Dislocation Tangle

The plastic deformation mechanism of Ti-55531 alloy with bimodal microstructure was investigated by compression testing at room temperature. The bimodal microstructure was composed of equiaxed primary α phase (αp) and transformed β (βtrans) that consisted of acicular secondary α phase (αs) and residual β phase (βr). In the initial stage of deformation, the αp grains first underwent plastic deformation, the dislocations germinated and increased, forming the dislocation loop with the dislocation free zone in αp at the true stain of 0.083. With the true strain subsequently increasing to 0.105, the dislocation tangle and dislocation pile-up occurred in αp, and a lot of dislocations were also activated in most of αs. Moreover, the dislocation density was increasing gradually in βr with the adding of strain. Finally, the dislocation pile-up and dislocation tangle appeared in αs and βr at the true strain of 0.163. The whole deformation process was coordinated by αp, αs and βr. They accommodated mutually and completed deformation together.

Positron annihilation in fatigued copper

1982 ◽  
Vol 60 (2) ◽  
pp. 201-204 ◽  
Author(s):  
S. Kupca ◽  
D. P. Kerr ◽  
B. G. Hogg ◽  
Z. S. Basinski
Keyword(s):  
Single Crystals ◽  
Point Defects ◽  
High Purity ◽  
Low Temperatures ◽  
Annealing Process ◽  
Simple Diffusion ◽  
Diffusion Limited ◽  
Annealing Study ◽  
Positron Lifetimes ◽  
Trapping Process

Positron lifetimes have been measured in an isochronal annealing study of dynamically fatigued, high purity Cu single crystals. Decomposition of the lifetime spectra into two components results in a description of the annealing process in terms of the lifetime and fraction of trapped positrons. Positron lifetimes were also determined at a series of low temperatures (10–300 K) at different stages of annealing. The lifetime of positrons trapped at point defects is found to vary with temperature indicating that a description of the trapping process according to a simple diffusion limited model is not applicable.

scholarly journals Parameter Screening in Microfluidics Based Hydrodynamic Single-Cell Trapping

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
B. Deng ◽  
X. F. Li ◽  
D. Y. Chen ◽  
L. D. You ◽  
J. B. Wang ◽  
...  
Keyword(s):  
Single Cell ◽  
Microfluidic Device ◽  
Single Cell Analysis ◽  
Fine Tuning ◽  
Trapping Efficiency ◽  
Cell Analysis ◽  
Cell Trapping ◽  
Micro Channels ◽  
Single Cell Trapping ◽  
Trapping Sites

Microfluidic cell-based arraying technology is widely used in the field of single-cell analysis. However, among developed devices, there is a compromise between cellular loading efficiencies and trapped cell densities, which deserves further analysis and optimization. To address this issue, the cell trapping efficiency of a microfluidic device with two parallel micro channels interconnected with cellular trapping sites was studied in this paper. By regulating channel inlet and outlet status, the microfluidic trapping structure can mimic key functioning units of previously reported devices. Numerical simulations were used to model this cellular trapping structure, quantifying the effects of channel on/off status and trapping structure geometries on the cellular trapping efficiency. Furthermore, the microfluidic device was fabricated based on conventional microfabrication and the cellular trapping efficiency was quantified in experiments. Experimental results showed that, besides geometry parameters, cellular travelling velocities and sizes also affected the single-cell trapping efficiency. By fine tuning parameters, more than 95% of trapping sites were taken by individual cells. This study may lay foundation in further studies of single-cell positioning in microfluidics and push forward the study of single-cell analysis.

The Cold Rolling Effect on the Precipitation Sequence and Microstructural Changes of an Al-Mg-Si Alloy

2019 ◽  
Vol 397 ◽  
pp. 51-58
Author(s):  
Hichem Farh ◽  
Toufik Ziar ◽  
Hanna Belghit ◽  
Mourad Khechba ◽  
Abdelouahab Noua ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Rolling Mill ◽  
Rolling Direction ◽  
Coarse Particles ◽  
Microstructural Properties ◽  
Precipitation Sequence ◽  
Initial Thickness ◽  
Cold Rolled ◽  
Mechanical And Microstructural Properties ◽  
Kinetics Of

The rolling operation consists of deforming the material by passing it between two rolls whose spacing is smaller than the initial thickness of the sample, the reduction in thickness is obtained discontinuously by successive passes in the rolling mill whose spacing between the cylinders gradually decreases. This operation can influence on the mechanical and microstructural properties of the deformed materials The effect of cold rolled on microstructural evolution and precipitation sequence in Al-Mg-Si alloy has been investigated by using optical microscopy and Differential Scanning Calorimetry (DSC) in this study . The results revealed that the distribution of the grains are elongated along the rolling direction. We also noted that i nsoluble coarse particles that originated during the manufacturing process of the alloy have become visible after the rolling processes . The dislocations generated by the plastic deformation during cooled rolling constitute preferential sites for the germination and the growth of the phases, which accelerates the kinetics of the precipitation.

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