Evolution of stress in individual grains and twins in a magnesium alloy aggregate

Aydıner, C. Can; Bernier, Joel V.; Clausen, B.; Lienert, U.; Tomé, Carlos N.; Brown, Donald W.

doi:10.1103/physrevb.80.024113

Cited by 160 publications

(96 citation statements)

References 17 publications

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“…Such an approach, however, does not take into account the complexity of the local stress state inside or in the vicinity of the primary twin (Aydiner et al 2009) or the mechanisms required for nucleating the secondary twin. As a consequence, the results have proved inconsistent with experimental observations.…”

Section: *Author For Correspondence (Irene@lanlgov)mentioning

confidence: 99%

Double twinning mechanisms in magnesium alloys via dissociation of lattice dislocations

et al. 2012

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In this work, we propose dislocation mechanisms for the formation of {1011}−{1012} double twin structures in hexagonal close packed (HCP) crystals through the nucleation of secondary twins within primary twin domains. The model considers that secondary twins associated with the most commonly observed double twin variants (i.e. type 1 and type 2) nucleate and thicken by a sequence of three distinct dissociation reactions of mixed basal dislocations. Provided that the less frequently observed double twin variants (i.e. type 3 and type 4) also form by a dislocation-based mechanism, we show that their development must proceed by a separate set of dissociation reactions involving pyramidal c + a slip dislocations. Mechanistic, crystallographic and energetic considerations indicate that the type 1 variant should be the most prevalent. The mechanisms proposed here would also apply to the analysis of {1013}−{1012} compound twins and HCP metals other than Mg that exhibit double twinning, such as titanium.

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Section: *Author For Correspondence (Irene@lanlgov)mentioning

confidence: 99%

Double twinning mechanisms in magnesium alloys via dissociation of lattice dislocations

et al. 2012

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“…Aydiner et al [93] used three-dimensional high-energy XRD to study the stress states within the twin and parent grains of a large grain Mg alloy in compression, where the {1012} tensile twin was activated. Resolution of the stress state of twin and parent revealed significantly different shear stresses, attributed to the constraint of the twin domain inhibiting deformation and leading to an increased back stress in the parent grain.…”

Section: (B) Twinning Deformation Studiesmentioning

confidence: 99%

On the mechanistic basis of deformation at the microscale in hexagonal close-packed metals

2015

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This is an overview of micromechanical deformation mechanisms in hexagonal close-packed metals. We start with an in-depth discussion of single-crystal behaviour concerning crystallographic slip, plastic anisotropy and deformation twinning. We move on to discuss some complexities involved in polycrystalline deformation and modelling approaches, focusing on rate effects in titanium alloys that are thought to play a significant role in dwell fatigue. We finish our review with a brief commentary on current understanding and state-of-the-art techniques, and outline some key areas where further study is recommended.

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“…Related arguments, based on self-strain accommodation have been proposed to account for the variant selection during double twinning in Mg-alloys [1,14,25]. Based on in-situ 3D-XRD observations Aydiner et al have reported that the stress state within a twin can be significantly different from that in the untwinned matrix [19]. For the grain tracked by Aydiner et al the stresses within each twin variant were observed to increase with increasing strain, though the stress values within each variant were different and differed to the applied macroscopic stress.…”

Section: Dependence On the Local Stress Conditionsmentioning

confidence: 99%

“…Although it is possible to determine the true twin shape within each grain using either serial sectioning [18] or a 3D-XRD approach [19], both of these methods are time consuming and require complicated apparatus. In order therefore to estimate the twin extent (variant volume fraction) within each grain some assumptions were made concerning the 3-dimensional geometry of the twin to allow the use of standard stereological methods [20].…”

Section: Twin Volume Fractionmentioning

confidence: 99%

Extension twin variant selection during uniaxial compression of a magnesium alloy

Pei

Godfrey

Jiang

et al. 2012

Materials Science and Engineering: A

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Samples of the magnesium alloy AZ31 have been deformed by compression to strains of 5% and 10% and microstructural observations made to investigate the activation of specific {10-12} extension twin variants. The twinning has been analyzed on a grain-by-grain basis for more than 260 grains to determine both the number of extension twin variants in each grain, and the volume fraction of each. At 5% strain approx. 30% of the grains contain twins corresponding to variants with the third or lower ranked Schmid factor, with the fraction increasing to 40% after 10% compression. A grain size effect is also observed in that smaller grains are less likely to contain lower ranked twin variants. For both 5% and 10% compression no clear relationship exists between the volume fraction of each twin variant in a given grain population and the Schmid factor for the twin variant. A positive linear relationship can be defined, however, between the maximum twinning fraction that a twin variant can reach and its Schmid factor. TITLE PAGE Abstract:Samples of the magnesium alloy AZ31 have been deformed by compression to strains of 5% and 10% and microstructural observations made to investigate the activation of specific {1012} extension twin variants. The twinning has been analyzed on a grain-by-grain basis for more than 260 grains to determine both the number of extension twin variants in each grain, and the volume fraction of each. At 5% strain approx. 30% of the grains contain twins corresponding to variants with the third or lower ranked Schmid factor, with the fraction increasing to 40% after 10% compression. A grain size effect is also observed in that smaller grains are less likely to contain lower ranked twin variants. For both 5% and 10% compression no clear relationship exists between the volume fraction of each twin variant in a given grain population and the Schmid factor for the twin variant. A positive linear relationship can be defined, however, between the maximum twinning fraction that a twin variant can reach and its Schmid factor.

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Evolution of stress in individual grains and twins in a magnesium alloy aggregate

Cited by 160 publications

References 17 publications

Double twinning mechanisms in magnesium alloys via dissociation of lattice dislocations

Double twinning mechanisms in magnesium alloys via dissociation of lattice dislocations

On the mechanistic basis of deformation at the microscale in hexagonal close-packed metals

Extension twin variant selection during uniaxial compression of a magnesium alloy

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