Geometrically necessary dislocations and strain-gradient plasticity: a few critical issues

Kubin, L.P.; Mortensen, Alicja

doi:10.1016/s1359-6462(02)00335-4

Cited by 753 publications

(150 citation statements)

References 20 publications

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“…A straightforward estimation of the geometrically necessary dislocation density (q GND ) can be obtained from KAM following Kubin and Mortensen: [28,30] q GND ¼ 1:5c# ub ; ½1…”

Section: A Grain Substructures Size and Boundary Densitymentioning

confidence: 99%

Effect of Prior Austenite Grain Size Refinement by Thermal Cycling on the Microstructural Features of As-Quenched Lath Martensite

Hidalgo

Santofimia

2016

Metall Mater Trans A

177

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Current trends in steels are focusing on refined martensitic microstructures to obtain high strength and toughness. An interesting manner to reduce the size of martensitic substructure is by reducing the size of the prior austenite grain (PAG). This work analyzes the effect of PAGS refinement by thermal cycling on different microstructural features of as-quenched lath martensite in a 0.3C-1.6Si-3.5Mn (wt pct) steel. The application of thermal cycling is found to lead to a refinement of the martensitic microstructures and to an increase of the density of high misorientation angle boundaries after quenching; these are commonly discussed to be key structural parameters affecting strength. Moreover, results show that as the PAGS is reduced, the volume fraction of retained austenite increases, carbides are refined and the concentration of carbon in solid solution as well as the dislocation density in martensite increase. All these microstructural modifications are related with the manner in which martensite forms from different prior austenite conditions, influenced by the PAGS.

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“…A straightforward estimation of the geometrically necessary dislocation density (q GND ) can be obtained from KAM following Kubin and Mortensen: [28,30] q GND ¼ 1:5c# ub ; ½1…”

Section: A Grain Substructures Size and Boundary Densitymentioning

confidence: 99%

Effect of Prior Austenite Grain Size Refinement by Thermal Cycling on the Microstructural Features of As-Quenched Lath Martensite

Hidalgo

Santofimia

2016

Metall Mater Trans A

177

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“…The parameter K depends on the postulated dislocation structure, that in practice may depend on straining conditions: it was proposed K = 1 for the bending [23] and K = 2 for the torsion [24] of a cylinder, assuming the presence of tilt and twist rotations, respectively. Since the present study is based on torsion tests, k = 2 was chosen.…”

Section: Estimation Of the Competing Forcesmentioning

confidence: 99%

Selective Growth of Low Stored Energy Grains During δ Sub-solvus Annealing in the Inconel 718 Nickel-Based Superalloy

Agnoli¹,

Bernacki

Logé

et al. 2015

Metall Mater Trans A

107

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The microstructure stability during d sub-solvus annealing in Inconel 718 was investigated, focusing on the conditions that may lead to the development of very large grains (about 100 lm) in a recrystallized fine grained matrix (4 to 5 lm) despite the presence of second-phase particles. Microstructure evolution was analyzed by EBSD (grain size, intragranular misorientation) and SEM (d phase particles). Results confirm that, in the absence of stored energy, the grain structure is controlled by the d phase particles, as predicted by the Smith-Zener equation. If the initial microstructure is strained (e < 0.1) before annealing, then low stored energy grains grow to a large extent, despite the Zener pinning forces exerted by the second-phase particles on the grain boundaries. Those selectively growing grains could be those of the initial microstructure that were the least deformed, or they could result from a nucleation process. The balance of three forces acting on boundary migration controls the growth process: if the sum of capillarity and stored energy driving forces exceeds the Zener pinning force, then selective grain growth occurs. Such phenomenon could be simulated, using a level set approach in a finite element context, by taking into account the three forces acting on boundary migration and by considering a realistic strain energy distribution (estimated from EBSD measurements).

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“…Measurements were performed on multiple grains showing different degrees of pile up. For each slit, multiple SEM images of resolution 768 x 768 pixels were acquired at high magnifications (field of view of [10][11][12][13][14][15] ) to ensure a high spatial resolution of measured displacement field. In order to obtain statistically sufficient data points, DIC was performed using a facet size of 19 x 19 pixels with a step width of 16 pixels.…”

Section: Residual Stress Measurement By Fib-dic Slit Millingmentioning

confidence: 99%

“…6(a)). GND density ( ) values from EBSD data were calculated using the strain gradient approach [15], [16], given by the expression:…”

Section: Residual Stress Measurement By Fib-dic Slit Millingmentioning

confidence: 99%

Experimental Determination and Theoretical Analysis of Local Residual Stress at Grain Scale

Basu¹,

Ocelík²,

Hosson³

2017

WIT Transactions on Engineering Sciences

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Grain/phase boundaries contribute significantly to build up of residual stresses, owing to varied plastic/thermal response of different grain orientations or phases during thermomechanical treatment. Hence, accurate quantification of such local scale stress gradients in commercial components is important in understanding their mechanical performance. The current work introduces a correlative method utilizing Electron Back Scattered Diffraction and Focused Ion Beam -Digital Image slit milling methodology to accurately determine spatially resolved stress profiles in the vicinity of grain boundaries using commercially pure titanium as a model material. Measured local stress gradients were in good agreement with local misorientation values. The role of dislocation-grain boundary interactions on buildup of local stress gradients is elucidated. Stress profiles near grain boundaries initially display non Hall-Petch characteristics, followed by a typical Hall-Petch type variation of "one over square root of distance". The observed trends allude to local stress relaxation mechanisms very close to the grain boundaries. The findings indicate that grain scale stress gradients can be significant in terms of playing a crucial role in macroscopic fatigue behavior.

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Geometrically necessary dislocations and strain-gradient plasticity: a few critical issues

Abstract: A few issues related to the modeling of size effects in terms of geometrically necessary dislocations (GNDs) are critically discussed, viz. strain hardening, length scale dependence, types of GND arrays. Consequences are drawn regarding the continuum modeling of size effects in plasticity.

Cited by 753 publications

References 20 publications

Effect of Prior Austenite Grain Size Refinement by Thermal Cycling on the Microstructural Features of As-Quenched Lath Martensite

Effect of Prior Austenite Grain Size Refinement by Thermal Cycling on the Microstructural Features of As-Quenched Lath Martensite

Selective Growth of Low Stored Energy Grains During δ Sub-solvus Annealing in the Inconel 718 Nickel-Based Superalloy

Experimental Determination and Theoretical Analysis of Local Residual Stress at Grain Scale

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