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Dierk Raabe - One of the best experts on this subject based on the ideXlab platform.
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Dislocation density distribution around an indent in single crystalline nickel comparing nonlocal crystal plasticity finite element predictions with experiments
Acta Materialia, 2014Co-Authors: C Reuber, Franz Roters, Philip Eisenlohr, Dierk RaabeAbstract:Abstract We present a physics-based constitutive model of Dislocation glide in metals that explicitly accounts for the redistribution of Dislocations due to their motion. The model parameterizes the complex microstructure by Dislocation densities of edge and screw character, which either occur with monopolar properties, i.e. a single Dislocation with positive or negative line sense, or with dipolar properties, i.e. two Dislocations of opposite line sense combined. The advantage of the model lies in the description of the Dislocation density evolution, which comprises the usual rate equations for Dislocation multiplication and annihilation, and formation and dissociation of Dislocation dipoles. Additionally, the spatial redistribution of Dislocations by slip is explicitly accounted for. This is achieved by introducing an advection term for the Dislocation density that turns the evolution equations for the Dislocation density from ordinary into partial differential equations. The associated spatial gradients of the Dislocation slip render the model nonlocal. The model is applied to wedge indentation in single-crystalline nickel. The simulation results are compared to published experiments (Kysar et al., 2010) in terms of the spatial distribution of lattice rotations and geometrically necessary Dislocations. In agreement with experiment, the predicted Dislocation fluxes lead to accumulation of geometrically necessary Dislocations around a vertical geometrical border with a high orientation gradient below the indenter that is decisive for the overall plastic response. A local model variant without Dislocation transport is not able to predict the influence of this geometrical transition zone correctly and is shown to behave markedly softer.
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Dislocation density distribution around an wedge indent in single crystalline nickel comparing non local crystal plasticity finite element predictions with experiments
11th World Congress on Computational Mechanics (WCCM XI) and 5th European Conference on Computational Mechanics (ECCM V)#N#, 2014Co-Authors: Franz Roters, Philip Eisenlohr, C Kords, Dierk RaabeAbstract:We present a physics-based constitutive model of Dislocation glide in metals that explicitly accounts for the redistribution of Dislocations due to their motion. The model parameterizes the complex microstructure by Dislocation densities of edge and screw character, which either occur with monopolar properties, i.e. a single Dislocation with positive or negative line sense, or with dipolar properties, i.e. two Dislocations of opposite line sense combined. The advantage of the model lies in the description of the Dislocation density evolution, which comprises the usual rate equations for Dislocation multiplication and annihilation, and formation and dissociation of Dislocation dipoles. Additionally, the spatial redistribution of Dislocations by slip is explicitly accounted for. This is achieved by introducing an advection term for the Dislocation density that turns the evolution equations for the Dislocation density from ordinary into partial differential equations. The associated spatial gradients of the Dislocation slip render the model nonlocal. The model is applied to wedge indentation in single-crystalline nickel. The simulation results are compared to published experiments (Kysar et al., 2010) in terms of the spatial distribution of lattice rotations and geometrically necessary Dislocations. In agreement with experiment, the predicted Dislocation fluxes lead to accumulation of geometrically necessary Dislocations around a vertical geometrical border with a high orientation gradient below the indenter that is decisive for the overall plastic response. A local model variant without Dislocation transport is not able to predict the influence of this geometrical transition zone correctly and is shown to behave markedly softer.
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effect of climb on Dislocation mechanisms and creep rates in γ strengthened ni base superalloy single crystals a discrete Dislocation dynamics study
Acta Materialia, 2013Co-Authors: Seyed Masood Hafez Haghighat, G Eggeler, Dierk RaabeAbstract:Abstract Creep of single-crystal superalloys is governed by Dislocation glide, climb, reactions and annihilation. Discrete three-dimensional (3D) Dislocation dynamics (DDD) simulations are used to study the evolution of the Dislocation substructure in a γ/γ′ microstructure of a single-crystal superalloy for different climb rates and loading conditions. A hybrid mobility law for glide and climb is used to map the interactions of Dislocations with γ′ cubes. The focus is on the early stages of creep, where Dislocation plasticity is confined to narrow γ channels. With enhancing climb mobility, the creep strain increases, even if the applied resolved shear stress is below the critical stress required for squeezing Dislocations into the γ channels. The simulated creep microstructure consists of long Dislocations and a network near the corners of the γ′ precipitate in the low-stress regime. In the high-stress regime, Dislocations squeeze into the γ channels, where they deposit Dislocation segments at the γ/γ′ interfaces. These observations are in good agreement with experimentally observed Dislocation structures that form during high-temperature and low-stress creep.
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simulation of Dislocation penetration through a general low angle grain boundary
Acta Materialia, 2012Co-Authors: B Liu, Philip Eisenlohr, Franz Roters, Dierk RaabeAbstract:The interaction of Dislocations with low-angle grain boundaries (LAGBs) is considered one important contribution to the mechanical strength of metals. Although LAGBs have been frequently observed in metals, little is known about how they interact with free Dislocations that mainly carry the plastic deformation. Using discrete Dislocation dynamics simulations, we are able to quantify the resistance of a LAGB—idealized as three sets of Dislocations that form a hexagonal Dislocation network—against lattice Dislocation penetration, and examine the associated Dislocation processes. Our results reveal that such a coherent internal boundary can massively obstruct and even terminate Dislocation transmission and thus make a substantial contribution to material strength.
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Dislocation interactions and low angle grain boundary strengthening
Acta Materialia, 2011Co-Authors: B Liu, Athanasios Arsenlis, Dierk Raabe, Philip Eisenlohr, Franz Roters, Gregg HommesAbstract:Abstract The transmission of an incoming Dislocation through a symmetrical low-angle tilt grain boundary (GB) is studied for {1 1 0}〈1 1 1〉 slip systems in body-centered cubic metals using discrete Dislocation dynamics (DD) simulations. The transmission resistance is quantified in terms of the different types of interactions between the incoming and GB Dislocations. Five different Dislocation interaction types are considered: collinear, mixed-symmetrical junction, mixed-asymmetrical junction, edge junction, and coplanar. Mixed-symmetrical junction formation events are found not only to cause a strong resistance against the incident Dislocation penetration, but also to transform the symmetrical low-angle tilt GB into a hexagonal network (a general low-angle GB). The interactions between the incident Dislocation and the GB Dislocations can form an array of 〈1 0 0〉 Dislocations (binary junctions) in non-coplanar interactions, or a single 〈1 0 0〉 Dislocation in coplanar interaction. We study how the transmission resistance depends on the mobility of 〈1 0 0〉 Dislocations. 〈1 0 0〉 Dislocations have usually been treated as immobile in DD simulations. In this work, we discuss and implement the mobility law for 〈1 0 0〉 Dislocations. As an example, we report how the mobility of 〈1 0 0〉 Dislocations affects the equilibrium configuration of a ternary Dislocation interaction.
Ze Zhang - One of the best experts on this subject based on the ideXlab platform.
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effect of lattice misfit on the evolution of the Dislocation structure in ni based single crystal superalloys during thermal exposure
Acta Materialia, 2016Co-Authors: Haibo Long, Sisi Xiang, Ze Zhang, Yanhui Chen, Qing Li, Jianxin ZhangAbstract:Abstract In this study, we investigate the movement of Dislocations in Ni-based superalloys under the influence of lattice misfit stresses between the ordered γ'-cuboids and the disordered γ-matrix during thermal exposure in the absence of an applied load. This study focuses on a different condition than the conventional creep testing, and thus offers a unique opportunity to study the intrinsic behavior of the alloy. The Dislocation density increases substantially with time during thermal exposure, leading to the formation of various configurations of Dislocation networks on the {100} γ/γ′ interfaces, including diamond-shaped, / mixed polygon-shaped and square-shaped networks. During thermal exposure, the b = 1 2 110 > native Dislocations first move and evolve into 60° mixed Dislocations along the directions on the {100} γ/γ′ interfaces, forming the diamond-shaped Dislocation networks. In the case of longer thermal exposures, the Dislocations further evolve into pure edge Dislocations along the on the {100} γ/γ′ interface, leading to the evolution of the diamond-shaped Dislocation networks into square-shaped networks, with the mixed / Dislocation networks as an intermediate stage during the transition. These movements occur by sweep glide in the {111} planes and diagonal climb on the {100} planes for the edge and mixed Dislocations and by cross-slip for the screw Dislocations. The driving force for all of these movements is the interaction between the normal misfit stresses and the edge components of the Burgers vectors of the Dislocations to relax the misfit stresses. An analysis based on the elastic strain energy considerations is presented to explain the driving forces for the Dislocation movements.
Hussein M. Zbib - One of the best experts on this subject based on the ideXlab platform.
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Discrete Dislocation dynamics simulation of cutting of γ′ precipitate and interfacial Dislocation network in Ni-based superalloys
International Journal of Plasticity, 2006Co-Authors: Kisaragi Yashiro, Fumiharu Kurose, Yusuke Nakashima, Keisuke Kubo, Yoshihiro Tomita, Hussein M. ZbibAbstract:Abstract We proposed a back force model for simulating Dislocations cutting into a γ′ precipitate, from the physical viewpoint of work for making or recovering an antiphase boundary (APB). The first Dislocation, or a leading partial of a superDislocation, is acted upon by a back force whose magnitude is equal to the APB energy. The second Dislocation, or a trailing partial of a superDislocation, is attracted by the APB with a force of the same magnitude. The model is encoded in a 3D discrete Dislocation dynamics (DDD) code and demonstrates that a superDislocation nucleates after two Dislocations pile up at the interface and that the width of Dislocations is naturally balanced by the APB energy and repulsion of Dislocations. The APB energy adopted here is calculated by ab initio analysis on the basis of the density functional theory (DFT). Then we applied our DDD simulations to more complicated cases, namely, Dislocations near the edges of a cuboidal precipitate and those at the γ/γ′ interface covered by an interfacial Dislocation network. The former simulation shows that Dislocations penetrate into a γ′ precipitate as a superDislocation from the edge of the cube, when running around the cube to form Orowan loops. The latter reveals that Dislocations become wavy at the interface due to the stress field of the Dislocation network, then cut into the γ′ precipitate through the interspace of the network. Our model proposed here can be applied to study the dependence of the cutting resistance on the spacing of Dislocations in the interfacial Dislocation network.
Minsheng Huang - One of the best experts on this subject based on the ideXlab platform.
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Atomistic modeling of the interaction between matrix Dislocation and interfacial misfit Dislocation networks in Ni-based single crystal superalloy
Computational Materials Science, 2013Co-Authors: Zhenhuan Li, Minsheng HuangAbstract:Abstract To reveal the intrinsic strengthening mechanism in Ni-based single crystal superalloy, the interaction between matrix Dislocations and interfacial misfit Dislocation networks was modeled in this contribution via molecular dynamics (MD) method. Our results show that the role of interfacial Dislocation networks is very complex. On the one hand, the interfacial Dislocation networks can act as Dislocation sinks to absorb/accommodate the matrix Dislocations. During the accommodation process of matrix Dislocation by the networks, both the interfacial Lomer–Cottrell locks and a[1 0 0] Dislocation junctions are formed, which stabilize and strengthen the interfacial Dislocation networks. On the other hand, the interfacial Dislocation networks can provide Dislocation pins to prevent the matrix Dislocations from cutting into the γ′ precipitate. These matrix Dislocation segments pinned at the phase interface can serve as Frank–Read sources with their length being about half of the Dislocation network spacing, providing an explanation for the effect of Dislocation network spacing on the creep strength of the Ni-based single crystal superalloy.
Kisaragi Yashiro - One of the best experts on this subject based on the ideXlab platform.
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discrete Dislocation dynamics simulation of interfacial Dislocation network in gamma gamma prime microstructure of ni based superalloys
Cmes-computer Modeling in Engineering & Sciences, 2006Co-Authors: Kisaragi Yashiro, Yusuke Nakashima, Yoshihiro TomitaAbstract:A simple back force model is proposed for a Dislocation cutting into γ � precipitate, taking the work for making and recovering an anti-phase boundary (APB) into account. The first Dislocation, or a leading partial of a superDislocation, is acted upon by a back force whose magnitude is equal to the APB energy. The second dis- location, or a trailing partial of a superDislocation, is at- tracted by the APB with a force of the same magnitude. The model is encoded in the 3D discrete Dislocation dy- namics (DDD) code and applied to the cutting behavior of Dislocations at a γ/γ � interface covered by an interfa- cial Dislocation network. Dislocations are generated from Frank-Read sources and approach the interface. The first Dislocation piles up at the interface not by the stress field of the network but by the back force against making an APB. The second Dislocation, however, stands off from the interface by the stress field of the first Dislocation and the Dislocation network. The finer mesh of the network, the further the second Dislocation piles up. These two Dislocations cut into the precipitate forming a superdis- location under the force from follow-on Dislocations. It is also clarified that the penetration takes place from the interspace of the network.
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Discrete Dislocation dynamics simulation of cutting of γ′ precipitate and interfacial Dislocation network in Ni-based superalloys
International Journal of Plasticity, 2006Co-Authors: Kisaragi Yashiro, Fumiharu Kurose, Yusuke Nakashima, Keisuke Kubo, Yoshihiro Tomita, Hussein M. ZbibAbstract:Abstract We proposed a back force model for simulating Dislocations cutting into a γ′ precipitate, from the physical viewpoint of work for making or recovering an antiphase boundary (APB). The first Dislocation, or a leading partial of a superDislocation, is acted upon by a back force whose magnitude is equal to the APB energy. The second Dislocation, or a trailing partial of a superDislocation, is attracted by the APB with a force of the same magnitude. The model is encoded in a 3D discrete Dislocation dynamics (DDD) code and demonstrates that a superDislocation nucleates after two Dislocations pile up at the interface and that the width of Dislocations is naturally balanced by the APB energy and repulsion of Dislocations. The APB energy adopted here is calculated by ab initio analysis on the basis of the density functional theory (DFT). Then we applied our DDD simulations to more complicated cases, namely, Dislocations near the edges of a cuboidal precipitate and those at the γ/γ′ interface covered by an interfacial Dislocation network. The former simulation shows that Dislocations penetrate into a γ′ precipitate as a superDislocation from the edge of the cube, when running around the cube to form Orowan loops. The latter reveals that Dislocations become wavy at the interface due to the stress field of the Dislocation network, then cut into the γ′ precipitate through the interspace of the network. Our model proposed here can be applied to study the dependence of the cutting resistance on the spacing of Dislocations in the interfacial Dislocation network.
