The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Dierk Raabe - One of the best experts on this subject based on the ideXlab platform.
-
on the role of the collinear Dislocation Interaction in deformation patterning and laminate formation in single crystal plasticity
Mechanics of Materials, 2018Co-Authors: Ding Wang, Franz Roters, Martin Diehl, Dierk RaabeAbstract:Abstract We investigate the reasons for severe deformation patterning observed in crystal plasticity simulations of an fcc nickel single crystal with initial near-Copper orientation deformed in plane strain compression. The resulting strain partitioning in the form of alternating parallel bands initiates at a very early loading stage, i.e.
-
Dislocation Interaction and twinning induced plasticity in face centered cubic fe mn c micro pillars
Acta Materialia, 2017Co-Authors: Wonseok Choi, Stefanie Sandlobes, Nataliya Malyar, Christoph Kirchlechner, Sandra Kortekerzel, Gerhard Dehm, Bruno C De Cooman, Dierk RaabeAbstract:Abstract Deformation twinning contributes to a high work-hardening rate through modification of the Dislocation structure and a dynamic Hall-Petch effect in polycrystalline steel. Due to the well-defined compression axis and limited deformation volume of micro-pillars, micro-compression testing is a suitable method to investigate the mechanisms of deformation twinning and the Interactions of Dislocations with twin boundaries. The material investigated is an austenitic Fe-22 wt%Mn-0.6 wt%C twining-induced plasticity steel. Micro-pillars oriented preferentially for deformation twinning and Dislocation glide are compressed and the activated deformation systems are characterized. We observe that deformation twinning induces higher flow stresses and a more unstable work-hardening behavior than Dislocation glide, while Dislocation glide dominated deformation results in a stable work-hardening behavior. The higher flow stresses and unstable work-hardening behavior in micro-pillars oriented for deformation twinning are assumed to be caused by the activation of secondary slip systems and accumulated plastic deformation.
-
Dislocation Interactions and low angle grain boundary strengthening
Acta Materialia, 2011Co-Authors: B Liu, Dierk Raabe, Philip Eisenlohr, Franz Roters, A Arsenlis, G 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.
-
atomic scale mechanisms of deformation induced cementite decomposition in pearlite
Acta Materialia, 2011Co-Authors: Yujiao Li, Dierk Raabe, C Borchers, Pyuckpa Choi, S Westerkamp, Shoji Goto, R KirchheimAbstract:Pearlitic steel can exhibit tensile strengths higher than 5 GPa after severe plastic deformation, where the deformation promotes a refinement of the lamellar structure and cementite decomposition. However, a convincing correlation between deformation and cementite decomposition in pearlite is still absent. In the present work, a local electrode atom probe was used to characterize the microstructural evolution of pearlitic steel, cold-drawn with progressive strains up to 5.4. Transmission electron microscopy was also employed to perform complementary analyses of the microstructure. Both methods yielded consistent results. The overall carbon content in the detected volumes as well as the carbon concentrations in ferrite and cementite were measured by atom probe. In addition, the thickness of the cementite filaments was determined. In ferrite, we found a correlation of carbon concentration with the strain, and in cementite, we found a correlation of carbon concentration with the lamella thickness. Direct evidence for the formation of cell/subgrain boundaries in ferrite and segregation of carbon atoms at these defects was found. Based on these findings, the mechanisms of cementite decomposition are discussed in terms of carbon–Dislocation Interaction.
Brian D. Wirth - One of the best experts on this subject based on the ideXlab platform.
-
Molecular dynamics simulations of Dislocation Interaction with voids in nickel
Computational Materials Science, 2011Co-Authors: Aude Simar, Hyon-jee Lee Voigt, Brian D. WirthAbstract:A high density of voids is expected to form in irradiated face centered cubic metals, which can have a negative impact on the ductility and cause an increasing strength. Molecular dynamics simulations of the Interaction between gliding dissociated edge Dislocations and voids in nickel have been performed to investigate the effect of the void size, the corresponding detachment mechanism, and dynamic effects of the Dislocation on the obstacle strength. As expected, the void strength is observed to increase with increasing void size. The Dislocation Interaction and detachment process are determined by the applied shear stress, the repulsive Interaction between partial Dislocations and the image Interaction between the partial Dislocations and the void surface. For voids with a diameter smaller than 2 nm, the repulsive stress between the partials dominates, resulting in the detachment of the leading partial from the void while the trailing partial remains pinned. Consequently, the detachment process and obstacle strength are controlled by the trailing partial. For voids with a diameter larger than 2 nm, the attraction between the dissociated Dislocations and the void dominates causing the detachment process and void strength to be influenced by both partials individually. This transition in detachment process at a void diameter of 2 nm is consistent with other research, and this transition is shown to be dependent on the void separation distance along the Dislocation line and the dissociation distance between the partials, thus the stacking fault energy. Finally, by comparing the quasi-static and dynamic simulation results, an estimate for the static detachment stress is proposed in terms of the dynamic detachment stress and the Dislocation velocity after detachment.
-
molecular dynamics simulation of the Interaction between a mixed Dislocation and a stacking fault tetrahedron
Philosophical Magazine, 2009Co-Authors: Brian D. WirthAbstract:A high number-density of nanometer-sized stacking fault tetrahedra are commonly found during irradiation of low stacking fault energy metals. The stacking fault tetrahedra act as obstacles to Dislocation motion leading to increased yield strength and decreased ductility. Thus, an improved understanding of the Interaction between gliding Dislocations and stacking fault tetrahedra are critical to reliably predict the mechanical properties of irradiated materials. Many studies have investigated the Interaction of a screw or edge Dislocation with a stacking fault tetrahedron (SFT). However, atomistic studies of a mixed Dislocation Interaction with an SFT are not available, even though mixed Dislocations are the most common. In this paper, molecular dynamics simulation results of the Interaction between a mixed Dislocation and an SFT in face-centered cubic copper are presented. The Interaction results in shearing, partial absorption, destabilization or simple bypass of the SFT, depending on the Interaction geo...
-
molecular dynamics simulation of screw Dislocation Interaction with stacking fault tetrahedron in face centered cubic cu
Journal of Materials Research, 2007Co-Authors: Jaehyeok Shim, Brian D. WirthAbstract:The Interaction of a gliding screw Dislocation with stacking fault tetrahedron (SFT) in face-centered cubic (fcc) copper (Cu) was studied using molecular dynamics simulations. Upon intersection, the screw Dislocation spontaneously cross slips on the SFT face. One of the cross-slipped Shockley partials glides toward the SFT base, partially absorbing the SFT. At low applied stress, partial absorption produces a superjog, with detachment of the trailing Shockley partial via an Orowan process. This leaves a small perfect SFT and a truncated base behind, which subsequently form a sheared SFT with a pair of opposite sense ledges. At higher applied shear stress, the ledges can self-heal by gliding toward an SFT apex and transform the sheared SFT into a perfect SFT. However, complete absorption or collapse of an SFT (or sheared SFT) by a moving screw Dislocation is not observed. These observations provide insights into defect-free channel formation in deformed irradiated Cu.
V G Gavriljuk - One of the best experts on this subject based on the ideXlab platform.
-
hydrogen migration and hydrogen Dislocation Interaction in austenitic steels and titanium alloy in relation to hydrogen embrittlement
International Journal of Hydrogen Energy, 2017Co-Authors: S M Teus, Dmytro G Savvakin, O M Ivasishin, V G GavriljukAbstract:Abstract CrNi austenitic steels and titanium alloy Ti-10V-2Fe-3Al are studied aiming to clarify a reason for difference between two classes of engineering materials in their sensitivity to hydrogen brittleness. Using ab initio calculations, it is found that hydrogen increases density of electron states at the Fermi level in both materials except for its decrease in the titanium alloy at extremely high hydrogen contents. Migration of hydrogen atoms and their Interaction with Dislocations are studied using mechanical spectroscopy. The enthalpies of hydrogen atoms migration and their binding to Dislocations, as well as temperature for condensation of hydrogen clouds around Dislocations, are shown to be significantly larger in austenitic steels in comparison with the β titanium alloy. This is a reason for lower temperature range of hydrogen embrittlement in the titanium alloys. The different hydrogen effect in the studied materials and usage of hydrogen as temporary alloying element increasing plasticity of titanium alloys in the course of their processing are interpreted within the frame of HELP theory.
-
decomposition of cementite in pearlitic steel due to plastic deformation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: V G GavriljukAbstract:Abstract The available experimental data and hypotheses concerning cementite decomposition during the cold work of pearlitic steels are reviewed. The results of studies performed using thermomagnetic analysis, Mossbauer spectroscopy, internal friction and APFIM are used to discuss the mechanism governing cementite decomposition. The following features of this phenomenon seem to be important: (i) the fraction of the decomposed cementite increases with the refining of the initial pearlitic structure, i.e. with the increase of the ferrite–cementite interfacial area; (ii) the decomposition effect saturates as strain increases; (iii) carbon–Dislocation Interaction in ferrite and MeC bonding in cementite have a strong influence on cementite decomposition. The conclusion is made that cementite decomposition is controlled by the transfer of carbon atoms from cementite to Dislocations accumulated near the interface during deformation. This is because the binding enthalpy between carbon atoms and Dislocations in ferrite exceeds the solution heat of cementite. Some relevant effects of cementite decomposition in practice are discussed.
V S Zolotorevsky - One of the best experts on this subject based on the ideXlab platform.
-
study of work hardening of quenched and naturally aged al mg and al cu alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: Yu N Zolotorevsky, A N Solonin, Yu A Churyumov, V S ZolotorevskyAbstract:Abstract A comparative study on the work hardening of Al–Mg and Al–Cu alloys was carried out using a Kocks–Mecking–Estrin type analysis of stress–strain curves obtained in tension tests at constant loading rate. As a result of the analysis, dependencies of forest Dislocation storage and dynamic recovery rates on the Mg and Cu concentration have been derived. The work hardening behavior and the microstructure formation in the Al–Mg and Al–Cu alloys were shown to be similar despite the opposite effects of Cu and Mg on stacking fault energy as well as the differences in solute atom size and friction stress. The influence of alloying on the work hardening peculiarities and the Dislocation substructure evolution was discussed in connection with the effects of solute–Dislocation Interaction.
Stefanie Sandlobes - One of the best experts on this subject based on the ideXlab platform.
-
Dislocation Interaction and twinning induced plasticity in face centered cubic fe mn c micro pillars
Acta Materialia, 2017Co-Authors: Wonseok Choi, Stefanie Sandlobes, Nataliya Malyar, Christoph Kirchlechner, Sandra Kortekerzel, Gerhard Dehm, Bruno C De Cooman, Dierk RaabeAbstract:Abstract Deformation twinning contributes to a high work-hardening rate through modification of the Dislocation structure and a dynamic Hall-Petch effect in polycrystalline steel. Due to the well-defined compression axis and limited deformation volume of micro-pillars, micro-compression testing is a suitable method to investigate the mechanisms of deformation twinning and the Interactions of Dislocations with twin boundaries. The material investigated is an austenitic Fe-22 wt%Mn-0.6 wt%C twining-induced plasticity steel. Micro-pillars oriented preferentially for deformation twinning and Dislocation glide are compressed and the activated deformation systems are characterized. We observe that deformation twinning induces higher flow stresses and a more unstable work-hardening behavior than Dislocation glide, while Dislocation glide dominated deformation results in a stable work-hardening behavior. The higher flow stresses and unstable work-hardening behavior in micro-pillars oriented for deformation twinning are assumed to be caused by the activation of secondary slip systems and accumulated plastic deformation.