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Gerhard Dehm - One of the best experts on this subject based on the ideXlab platform.
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dislocation slip transmission through a coherent σ3 111 copper Twin Boundary strain rate sensitivity activation volume and strength distribution function
Acta Materialia, 2018Co-Authors: Nataliya Malyar, Gerhard Dehm, Blazej Grabowski, Christoph KirchlechnerAbstract:Abstract We present the first measurement of the strain rate sensitivity of the ideal dislocation slip transmission through a coherent Σ3{111} copper Twin Boundary. For this purpose we have deformed 129 geometrically identical samples at different strain rates. The micron-sized samples are either single crystalline (87 pillars) or contain one vertical Σ3{111} Twin Boundary (42 pillars). The strain rate sensitivity of the ideal slip transmission event is 0.015 ± 0.009. This value is considerably lower than the strain rate sensitivity observed for nano-Twinned bulk materials, which is addressed to multiple simultaneously activated deformation processes present in the latter case. The activation volume of the ideal slip transmission points towards a cross-slip like transmission process of dislocations through the Twin Boundary. Furthermore, the high number of geometrically identical samples is used to discuss the ability to identify the strength distribution function of micropillars.
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on the nature of Twin Boundary associated strengthening in fe mn c steel
Scripta Materialia, 2018Co-Authors: Wonseok Choi, Stefanie Sandlobes, Nataliya Malyar, Christoph Kirchlechner, Sandra Kortekerzel, Gerhard Dehm, Pyuckpa Choi, Dierk RaabeAbstract:Abstract We unravel the nature of Twin Boundary-associated strengthening in Fe-Mn-C Twinning-induced plasticity steel (TWIPs) by micro-pillar compression tests. Dislocation interactions with a coherent Twin Boundary and their role on strain hardening were investigated. The results indicate that Twin-matrix bundles dynamically introduced by deformation Twinning and their interaction with dislocations are required for strengthening Fe-Mn-C TWIPs, while single coherent Twin boundaries enable dislocation transmission. Correlative studies on orientation dependent deformation mechanisms, detailed dislocation-Twin Boundary interactions, and the resulting local stress-strain responses suggest that Twin Boundary-associated strengthening is primarily caused by the reduction of the mean free dislocation path in nano-Twinned microstructures.
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formation of dislocation networks in a coherent cu σ3 1 1 1 Twin Boundary
Scripta Materialia, 2015Co-Authors: Jong Bae Jeon, Gerhard DehmAbstract:Molecular dynamics simulations were performed to investigate dislocation network formations in a coherent Twin Boundary in Cu. Depending on the activated glide system, the initial flawless Twin Boundary can be heavily or sparsely decorated by a dislocation network. The dislocation mechanism leading to a heavy dislocation network at the Twin Boundary and its consequence on mechanical properties will be discussed.
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Internal and external stresses: In situ TEM compression of Cu bicrystals containing a Twin Boundary
Scripta Materialia, 2015Co-Authors: Peter Julian Imrich, Christoph Kirchlechner, Daniel Kiener, Gerhard DehmAbstract:Uniaxial compression experiments on single- and Twinned bicrystalline Cu samples using conventional and scanning in situ transmission electron microscopy reveal no increase in flow stress for the bicrystals. Dislocation curvature and dislocation source size analysis combined with indenter force measurements show agreement between local internal stresses acting on the dislocations and external stresses imposed by the indenter, indicating no stress concentrations due to the Twin Boundary. Furthermore, the dislocation density evolution shows stochastic variations but never a complete dislocation starvation.
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differences in deformation behavior of bicrystalline cu micropillars containing a Twin Boundary or a large angle grain Boundary
Acta Materialia, 2014Co-Authors: Peter Julian Imrich, Christoph Kirchlechner, Christian Motz, Gerhard DehmAbstract:Abstract Micrometer-sized compression pillars containing a grain Boundary are investigated to better understand under which conditions grain boundaries have a strengthening effect. The compression experiments were performed on focused ion beam fabricated micrometer-sized bicrystalline Cu pillars including either a large-angle grain Boundary (LAGB) or a coherent Twin Boundary (CTB) parallel to the compression axis and additionally on single-crystalline reference samples. Pillars containing a LAGB show increased strength, stronger hardening and smaller load drops compared to single crystals and exhibit a bent Boundary and pillar shape. Samples with a CTB show no major difference in stress–strain data compared to the corresponding single-crystalline samples. This is due to the special orientation and symmetry of the Twin Boundary and is reflected in a characteristic pillar shape after deformation. The experimental findings can be related to the dislocation–Boundary interactions at the different grain boundaries and are compared with three-dimensional discrete dislocation dynamics simulations.
Christoph Kirchlechner - One of the best experts on this subject based on the ideXlab platform.
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dislocation slip transmission through a coherent σ3 111 copper Twin Boundary strain rate sensitivity activation volume and strength distribution function
Acta Materialia, 2018Co-Authors: Nataliya Malyar, Gerhard Dehm, Blazej Grabowski, Christoph KirchlechnerAbstract:Abstract We present the first measurement of the strain rate sensitivity of the ideal dislocation slip transmission through a coherent Σ3{111} copper Twin Boundary. For this purpose we have deformed 129 geometrically identical samples at different strain rates. The micron-sized samples are either single crystalline (87 pillars) or contain one vertical Σ3{111} Twin Boundary (42 pillars). The strain rate sensitivity of the ideal slip transmission event is 0.015 ± 0.009. This value is considerably lower than the strain rate sensitivity observed for nano-Twinned bulk materials, which is addressed to multiple simultaneously activated deformation processes present in the latter case. The activation volume of the ideal slip transmission points towards a cross-slip like transmission process of dislocations through the Twin Boundary. Furthermore, the high number of geometrically identical samples is used to discuss the ability to identify the strength distribution function of micropillars.
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on the nature of Twin Boundary associated strengthening in fe mn c steel
Scripta Materialia, 2018Co-Authors: Wonseok Choi, Stefanie Sandlobes, Nataliya Malyar, Christoph Kirchlechner, Sandra Kortekerzel, Gerhard Dehm, Pyuckpa Choi, Dierk RaabeAbstract:Abstract We unravel the nature of Twin Boundary-associated strengthening in Fe-Mn-C Twinning-induced plasticity steel (TWIPs) by micro-pillar compression tests. Dislocation interactions with a coherent Twin Boundary and their role on strain hardening were investigated. The results indicate that Twin-matrix bundles dynamically introduced by deformation Twinning and their interaction with dislocations are required for strengthening Fe-Mn-C TWIPs, while single coherent Twin boundaries enable dislocation transmission. Correlative studies on orientation dependent deformation mechanisms, detailed dislocation-Twin Boundary interactions, and the resulting local stress-strain responses suggest that Twin Boundary-associated strengthening is primarily caused by the reduction of the mean free dislocation path in nano-Twinned microstructures.
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Internal and external stresses: In situ TEM compression of Cu bicrystals containing a Twin Boundary
Scripta Materialia, 2015Co-Authors: Peter Julian Imrich, Christoph Kirchlechner, Daniel Kiener, Gerhard DehmAbstract:Uniaxial compression experiments on single- and Twinned bicrystalline Cu samples using conventional and scanning in situ transmission electron microscopy reveal no increase in flow stress for the bicrystals. Dislocation curvature and dislocation source size analysis combined with indenter force measurements show agreement between local internal stresses acting on the dislocations and external stresses imposed by the indenter, indicating no stress concentrations due to the Twin Boundary. Furthermore, the dislocation density evolution shows stochastic variations but never a complete dislocation starvation.
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differences in deformation behavior of bicrystalline cu micropillars containing a Twin Boundary or a large angle grain Boundary
Acta Materialia, 2014Co-Authors: Peter Julian Imrich, Christoph Kirchlechner, Christian Motz, Gerhard DehmAbstract:Abstract Micrometer-sized compression pillars containing a grain Boundary are investigated to better understand under which conditions grain boundaries have a strengthening effect. The compression experiments were performed on focused ion beam fabricated micrometer-sized bicrystalline Cu pillars including either a large-angle grain Boundary (LAGB) or a coherent Twin Boundary (CTB) parallel to the compression axis and additionally on single-crystalline reference samples. Pillars containing a LAGB show increased strength, stronger hardening and smaller load drops compared to single crystals and exhibit a bent Boundary and pillar shape. Samples with a CTB show no major difference in stress–strain data compared to the corresponding single-crystalline samples. This is due to the special orientation and symmetry of the Twin Boundary and is reflected in a characteristic pillar shape after deformation. The experimental findings can be related to the dislocation–Boundary interactions at the different grain boundaries and are compared with three-dimensional discrete dislocation dynamics simulations.
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in situ observation of stress induced stochastic Twin Boundary motion in off stoichiometric nimnga single crystals
Applied Physics Letters, 2013Co-Authors: Rozaliya Barabash, Christoph Kirchlechner, O Robach, O Ulrich, Jeansebastien Micha, A Sozinov, Oleg M BarabashAbstract:In-situ X-ray microdiffraction is used to illuminate the physics of non-uniform stochastic motion of type II Twin boundaries in NiMnGa Twinned crystals during external stress field loading. Asymmetry between tensile and compressive loading and a large hysteresis loop were found. The formation of local strained regions precedes each Boundary movement. The location of strained regions adjusts to the position of the Twin Boundary. Abrupt motion of the Boundary correlates with corresponding spikes at the load/displacement curve.
O Kraft - One of the best experts on this subject based on the ideXlab platform.
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in situ tem study of Twin Boundary migration in sub micron be fibers
Acta Materialia, 2015Co-Authors: Frederic Mompiou, Marc Legros, Charlotte Ensslen, O KraftAbstract:Abstract Deformation Twinning in hexagonal crystals is often considered as a way to palliate lack of independent slip systems. This mechanism might be either exacerbated or shut down in small-scale crystals whose mechanical behavior can significantly deviate from bulk materials. Here, we show that sub-micron beryllium fibers initially free of dislocation and tensile tested in situ in a transmission electron microscope (TEM) deform by a { 1 0 1 ¯ 2 } 〈 1 0 1 ¯ 0 〉 Twin thickening. The propagation speed of the Twin Boundary seems to be entirely controlled by the nucleation of Twinning dislocations directly from the surface. The shear produced is in agreement with the repeated lateral motion of Twinning dislocations. We demonstrate that the activation volume ( V ) associated with the Twin Boundary propagation can be retrieved from the measure of the Twin Boundary speed as the stress decreases as in a classical relaxation mechanical test. The value of V ≈ 1.6 ± 0.4 × 10 - 28 m 3 is comparable to the value expected from surface nucleation.
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In situ TEM study of Twin Boundary migration in sub-micron Be fibers
Acta Materialia, 2015Co-Authors: Frederic Mompiou, Marc Legros, Charlotte Ensslen, O KraftAbstract:Deformation Twinning in hexagonal crystals is often considered as a way to palliate the lack of independent slip systems. This mechanism might be either exacerbated or shut down in small-scale crystals whose mechanical behavior can significantly deviate from bulk materials. Here, we show that sub-micron beryllium fibers initially free of dislocation and tensile tested in-situ in a transmission electron microscope (TEM) deform by a $\{ 10\bar{1}2 \}$ $\langle 10\bar{1}1 \rangle$ Twin thickening. The propagation speed of the Twin Boundary seems to be entirely controlled by the nucleation of Twinning dislocations directly from the surface. The shear produced is in agreement with the repeated lateral motion of Twinning dislocations. We demonstrate that the activation volume ($V$) associated with the Twin Boundary propagation can be retrieved from the measure of the Twin Boundary speed as the stress decreases as in a classical relaxation mechanical test. The value of $V \approx 8.3 \pm 3.3 \times 10^{-29}m^3$ is comparable to the value expected from surface nucleation. \textbf{This text is a revised version of the article published in Acta Materialia, 96 (2015) 57-65 (doi:10.1016/j.actamat.2015.06.016)}
Marc Legros - One of the best experts on this subject based on the ideXlab platform.
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in situ tem study of Twin Boundary migration in sub micron be fibers
Acta Materialia, 2015Co-Authors: Frederic Mompiou, Marc Legros, Charlotte Ensslen, O KraftAbstract:Abstract Deformation Twinning in hexagonal crystals is often considered as a way to palliate lack of independent slip systems. This mechanism might be either exacerbated or shut down in small-scale crystals whose mechanical behavior can significantly deviate from bulk materials. Here, we show that sub-micron beryllium fibers initially free of dislocation and tensile tested in situ in a transmission electron microscope (TEM) deform by a { 1 0 1 ¯ 2 } 〈 1 0 1 ¯ 0 〉 Twin thickening. The propagation speed of the Twin Boundary seems to be entirely controlled by the nucleation of Twinning dislocations directly from the surface. The shear produced is in agreement with the repeated lateral motion of Twinning dislocations. We demonstrate that the activation volume ( V ) associated with the Twin Boundary propagation can be retrieved from the measure of the Twin Boundary speed as the stress decreases as in a classical relaxation mechanical test. The value of V ≈ 1.6 ± 0.4 × 10 - 28 m 3 is comparable to the value expected from surface nucleation.
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In situ TEM study of Twin Boundary migration in sub-micron Be fibers
Acta Materialia, 2015Co-Authors: Frederic Mompiou, Marc Legros, Charlotte Ensslen, O KraftAbstract:Deformation Twinning in hexagonal crystals is often considered as a way to palliate the lack of independent slip systems. This mechanism might be either exacerbated or shut down in small-scale crystals whose mechanical behavior can significantly deviate from bulk materials. Here, we show that sub-micron beryllium fibers initially free of dislocation and tensile tested in-situ in a transmission electron microscope (TEM) deform by a $\{ 10\bar{1}2 \}$ $\langle 10\bar{1}1 \rangle$ Twin thickening. The propagation speed of the Twin Boundary seems to be entirely controlled by the nucleation of Twinning dislocations directly from the surface. The shear produced is in agreement with the repeated lateral motion of Twinning dislocations. We demonstrate that the activation volume ($V$) associated with the Twin Boundary propagation can be retrieved from the measure of the Twin Boundary speed as the stress decreases as in a classical relaxation mechanical test. The value of $V \approx 8.3 \pm 3.3 \times 10^{-29}m^3$ is comparable to the value expected from surface nucleation. \textbf{This text is a revised version of the article published in Acta Materialia, 96 (2015) 57-65 (doi:10.1016/j.actamat.2015.06.016)}
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atomic scale simulation of screw dislocation coherent Twin Boundary interaction in al au cu and ni
Acta Materialia, 2011Co-Authors: M Chassagne, Marc Legros, David RodneyAbstract:Abstract The influence of material and choice of interatomic potential on the interaction between an a /2〈1 1 0〉{1 1 1} screw dislocation and a Σ3{1 1 1}〈1 1 0〉 coherent Twin Boundary (CTB) is determined by simulating this process in a range of face-centered cubic metals modeled with a total of 10 embedded-atom method (EAM) potentials. Generalized stacking fault energies are computed, showing a linear relation between the stacking faut ( γ S ) and Twin energies, as well as between the unstable stacking fault ( γ US ) and unstable Twinning ( γ UT ) energies. We show that the reaction mechanism (absorption of the dislocation into the CTB or transmission into the Twinned region) and reaction stress depend strongly on the potential used, even for a given material and are controlled by the material parameter γ S / μb P (where μ is the shear modulus and b P the Shockley partial Burgers vector), rather than the sign of the ratio ( γ US − γ S )/( γ UT − γ S ), as proposed recently by Jin et al. [1] . Moreover, there exists a critical reaction stress, close to 400 MPa, independent of the potential, below which the dislocation is absorbed in the CTB and above which the dislocation is transmitted into the Twinned region. The simulations are discussed with respect to in situ transmission electron microscopy straining experiments in Cu that highlight the importance of thermally activated cross-slip in the interaction process and show that transmission across a Twin Boundary is possible but is most likely an indirect process.
Frederic Mompiou - One of the best experts on this subject based on the ideXlab platform.
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in situ tem study of Twin Boundary migration in sub micron be fibers
Acta Materialia, 2015Co-Authors: Frederic Mompiou, Marc Legros, Charlotte Ensslen, O KraftAbstract:Abstract Deformation Twinning in hexagonal crystals is often considered as a way to palliate lack of independent slip systems. This mechanism might be either exacerbated or shut down in small-scale crystals whose mechanical behavior can significantly deviate from bulk materials. Here, we show that sub-micron beryllium fibers initially free of dislocation and tensile tested in situ in a transmission electron microscope (TEM) deform by a { 1 0 1 ¯ 2 } 〈 1 0 1 ¯ 0 〉 Twin thickening. The propagation speed of the Twin Boundary seems to be entirely controlled by the nucleation of Twinning dislocations directly from the surface. The shear produced is in agreement with the repeated lateral motion of Twinning dislocations. We demonstrate that the activation volume ( V ) associated with the Twin Boundary propagation can be retrieved from the measure of the Twin Boundary speed as the stress decreases as in a classical relaxation mechanical test. The value of V ≈ 1.6 ± 0.4 × 10 - 28 m 3 is comparable to the value expected from surface nucleation.
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In situ TEM study of Twin Boundary migration in sub-micron Be fibers
Acta Materialia, 2015Co-Authors: Frederic Mompiou, Marc Legros, Charlotte Ensslen, O KraftAbstract:Deformation Twinning in hexagonal crystals is often considered as a way to palliate the lack of independent slip systems. This mechanism might be either exacerbated or shut down in small-scale crystals whose mechanical behavior can significantly deviate from bulk materials. Here, we show that sub-micron beryllium fibers initially free of dislocation and tensile tested in-situ in a transmission electron microscope (TEM) deform by a $\{ 10\bar{1}2 \}$ $\langle 10\bar{1}1 \rangle$ Twin thickening. The propagation speed of the Twin Boundary seems to be entirely controlled by the nucleation of Twinning dislocations directly from the surface. The shear produced is in agreement with the repeated lateral motion of Twinning dislocations. We demonstrate that the activation volume ($V$) associated with the Twin Boundary propagation can be retrieved from the measure of the Twin Boundary speed as the stress decreases as in a classical relaxation mechanical test. The value of $V \approx 8.3 \pm 3.3 \times 10^{-29}m^3$ is comparable to the value expected from surface nucleation. \textbf{This text is a revised version of the article published in Acta Materialia, 96 (2015) 57-65 (doi:10.1016/j.actamat.2015.06.016)}
