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Bruno C De Cooman - One of the best experts on this subject based on the ideXlab platform.

  • Twinning-Induced Plasticity (TWIP) steels
    Acta Materialia, 2018
    Co-Authors: Bruno C De Cooman, Yuri Estrin, Sung-kyu Kim
    Abstract:

    Abstract This article reviews original work and important new developments in the field of deformation behavior of high manganese face-centered cubic γ-Fe alloys. Owing to their exceptional mechanical properties, these alloys, referred to as twinning-Induced Plasticity, or TWIP, steels, have come to the fore as prime candidate materials for light-weight applications, notably in automotive, shipbuilding, and oil and gas industries. It is established that a superior combination of strength and ductility exhibited by TWIP steels is associated with a specific character of the variation of the dislocation density. The defining feature of TWIP steels is the small magnitude of the intrinsic stacking fault energy. In addition to limiting the dynamic recovery rate, the low stacking fault energy of TWIP steels results in the formation of isolated stacking faults and deformation twins, which reduces the dislocation mean free path. Both effects lead to an increased strain hardening rate. Despite the progress made, there are still considerable differences between the models proposed for the microstructural evolution during the deformation of TWIP steels and the concomitant strain hardening behavior. The review surveys the experimental literature, summarizes the current modeling concepts, and identifies the outstanding issues with TWIP steels that require the attention of the materials science community. Suggestions for the directions of future research on twinning-Induced Plasticity steels are offered.

  • effect of cu addition on the mechanical behavior of austenitic twinning Induced Plasticity steel
    Scripta Materialia, 2011
    Co-Authors: Sangwon Lee, Jinkyung Kim, Seokjae Lee, Bruno C De Cooman
    Abstract:

    The effect of the addition of copper on the mechanical behavior of a Fe–12%Mn–0.7%C–1.0%Al twinning-Induced Plasticity steel was investigated by analysis of the mechanical properties obtained in uniaxial tensile tests by means of a physically based constitutive model. The addition of copper was found to retard the kinetics of twin formation and influenced the type of serrations on the stress–strain curve. The copper additions also resulted in a remarkable increase in total elongation without a loss of strength.

  • effect of nitrogen on the critical strain for dynamic strain aging in high manganese twinning Induced Plasticity steel
    Scripta Materialia, 2011
    Co-Authors: Sangwon Lee, Jinkyung Kim, Seokjae Lee, Bruno C De Cooman
    Abstract:

    The effect of nitrogen on the dynamic strain again behavior of a Fe–18% Mn–0.6% C twinning-Induced Plasticity steel was investigated by means of in situ infrared thermography during tensile testing. The addition of nitrogen affected the initiation of the Portevin–Le Châtelier bands and the characteristic shape of the serrations on the stress–strain curve. Also, nitrogen additions resulted in an increase in the critical strain for dynamic strain aging.

  • austenite stability of ultrafine grained transformation Induced Plasticity steel with mn partitioning
    Scripta Materialia, 2011
    Co-Authors: Bruno C De Cooman
    Abstract:

    The factors leading to the room temperature stabilization of austenite were investigated for an ultrafine-grained 6 mass% Mn transformation-Induced Plasticity steel. The size effect of ultrafine austenite grain and the partitioning of Mn to austenite during intercritical annealing were the two main contributions to the austenite stability. Mechanical stabilization of the austenite was not a factor contributing to the austenite stability due to the very low dislocation density of the austenite grains.

  • effect of al on the stacking fault energy of fe 18mn 0 6c twinning Induced Plasticity
    Scripta Materialia, 2011
    Co-Authors: Jinkyung Kim, Seokjae Lee, Bruno C De Cooman
    Abstract:

    The effect of Al on the stacking fault energy (SFE) of Fe–18Mn–0.6C twinning-Induced Plasticity steel was investigated by means of weak-beam dark-field transmission electron microscopy. The SFE of Fe–18Mn–0.6C steel was measured to be 13 ± 3 mJ m−2 and the actual increase in SFE due to adding 1 wt.% Al was approximately +11.3 mJ m−2.

Dierk Raabe - One of the best experts on this subject based on the ideXlab platform.

  • a crystal Plasticity model for twinning and transformation Induced Plasticity
    Acta Materialia, 2016
    Co-Authors: Su Leen Wong, Manjunatha Madivala, U Prahl, Franz Roters, Dierk Raabe
    Abstract:

    Abstract A dislocation density-based crystal Plasticity model incorporating both transformation-Induced Plasticity (TRIP) and twinning-Induced Plasticity (TWIP) is presented. The approach is a physically-based model which reflects microstructure investigations of e -martensite, twins and dislocation structures in high manganese steels. Validation of the model was conducted using experimental data for a TRIP/TWIP Fe-22Mn-0.6C steel. The model is able to predict, based on the difference in the stacking fault energies, the activation of TRIP and/or TWIP deformation mechanisms at different temperatures.

  • Design of a twinning-Induced Plasticity high entropy alloy
    Acta Materialia, 2015
    Co-Authors: Yun Deng, Konda Gokuldoss Pradeep, Aleksander Kostka, Hauke Springer, Cemal Cem Tasan, Dierk Raabe
    Abstract:

    Abstract We introduce a liquid metallurgy synthesized, non-equiatomic Fe 40 Mn 40 Co 10 Cr 10 high entropy alloy that is designed to undergo mechanically-Induced twinning upon deformation at room temperature. Microstructure characterization, carried out using SEM, TEM and APT shows a homogeneous fcc structured single phase solid solution in the as-cast, hot-rolled and homogenized states. Investigations of the deformation substructures at specific strain levels with electron channeling contrast imaging (ECCI) combined with EBSD reveal a clear change in the deformation mechanisms of the designed alloy starting from dislocation slip to twinning as a function of strain. Such twinning Induced Plasticity has only been observed under cryogenic conditions in the equiatomic FeMnNiCoCr high entropy alloy. Thus, despite the decreased contribution of solid solution strengthening, the tensile properties of the introduced lean alloy at room temperature are found to be comparable to that of the well-studied five component FeMnNiCoCr system.

  • nanolaminate transformation Induced Plasticity twinning Induced Plasticity steel with dynamic strain partitioning and enhanced damage resistance
    Acta Materialia, 2015
    Co-Authors: Meimei Wang, Cemal Cem Tasan, Dirk Ponge, Ann Christin Dippel, Dierk Raabe
    Abstract:

    Abstract Conventional martensitic steels have limited ductility due to insufficient microstructural strain-hardening and damage resistance mechanisms. It was recently demonstrated that the ductility and toughness of martensitic steels can be improved without sacrificing the strength, via partial reversion of the martensite back to austenite. These improvements were attributed to the presence of the transformation-Induced Plasticity (TRIP) effect of the austenite phase, and the precipitation hardening (maraging) effect in the martensitic matrix. However, a full micromechanical understanding of this ductilizing effect requires a systematic investigation of the interplay between the two phases, with regards to the underlying deformation and damage micromechanisms. For this purpose, in this work, a Fe–9Mn–3Ni–1.4Al–0.01C (mass%) medium-Mn TRIP maraging steel is produced and heat-treated under different reversion conditions to introduce well-controlled variations in the austenite–martensite nanolaminate microstructure. Uniaxial tension and impact tests are carried out and the microstructure is characterized using scanning and transmission electron microscopy based techniques and post mortem synchrotron X-ray diffraction analysis. The results reveal that (i) the strain partitioning between austenite and martensite is governed by a highly dynamical interplay of dislocation slip, deformation-Induced phase transformation (i.e. causing the TRIP effect) and mechanical twinning (i.e. causing the twinning-Induced Plasticity effect); and (ii) the nanolaminate microstructure morphology leads to enhanced damage resistance. The presence of both effects results in enhanced strain-hardening capacity and damage resistance, and hence the enhanced ductility.

  • Microbanding mechanism in an Fe–Mn–C high-Mn twinning-Induced Plasticity steel
    Scripta Materialia, 2013
    Co-Authors: Ivan Gutiérrez-urrutia, Dierk Raabe
    Abstract:

    We study the microbanding mechanism in an Fe–22Mn–0.6C (wt.%) twinning-Induced Plasticity steel. Dislocation substructures were examined by electron channeling contrast imaging and electron backscatter diffraction. We observe a pronounced effect of the strain path on microbanding, which is explained in terms of Schmid’s law. Microbands created under shear loading have a non-crystallographic character. This is attributed to the microbanding mechanism and its relation with the dislocation substructure. Further insights into the dislocation configuration of microbands are provided.

  • hydrogen assisted failure in a twinning Induced Plasticity steel studied under in situ hydrogen charging by electron channeling contrast imaging
    Acta Materialia, 2013
    Co-Authors: Eiji Akiyama, Motomichi Koyama, Kaneaki Tsuzaki, Dierk Raabe
    Abstract:

    We investigated the hydrogen embrittlement of a Fe–18Mn–1.2%C (wt.%) twinning-Induced Plasticity steel, focusing on the influence of deformation twins on hydrogen-assisted cracking. A tensile test under ongoing hydrogen charging was performed at low strain rate (1.7 � 10 � 6 s � 1 ) to observe hydrogen-assisted cracking and crack propagation. Hydrogen-stimulated cracks and deformation twins were observed by electron channeling contrast imaging. We made the surprising observation that hydrogen-assisted cracking was initiated both at grain boundaries and also at deformation twins. Also, crack propagation occurred along both types of interfaces. Deformation twins were shown to assist intergranular cracking and crack propagation. The stress concentration at the tip of the deformation twins is suggested to play an important role in the hydrogen embrittlement of the Fe–Mn–C twining-Induced Plasticity steel.

Hyoung Seop Kim - One of the best experts on this subject based on the ideXlab platform.

  • novel co rich high performance twinning Induced Plasticity twip and transformation Induced Plasticity trip high entropy alloys
    Scripta Materialia, 2019
    Co-Authors: Daixiu Wei, Hyoung Seop Kim, Jing Jiang, Weicheng Heng, Yuichiro Koizumi, Won Mi Choi, Byeongjoo Lee, Hidemi Kato, Akihiko Chiba
    Abstract:

    Abstract The equiatomic CoCrMnNiFe high-entropy alloy (HEA) has attracted much attention owing to its exceptional mechanical properties. Here, we designed novel face-centered cubic (fcc) phase Co-rich non-equiatomic CoCrMnNiFe HEAs with tensile properties superior to the counterparts, derived from lowering stacking fault energy (SFE) via modifying constituent concentrations. The decrease of Mn, Ni, Fe meanwhile increase of Co, Cr concentrations does reduce the SFE value, based on ab initio and thermodynamics calculations. Hereinto, Co35Cr20Mn15Ni15Fe15 and Co35Cr25Mn15Ni15Fe10 HEAs overcame the strength-ductility trade-off, contributing to twinning-Induced Plasticity (TWIP) or transformation-Induced Plasticity (TRIP) effects, respectively. The present study sheds light on developing high performance HEAs.

  • Suppressed deformation instability in the twinning-Induced Plasticity steel-cored three-layer steel sheet
    Acta Materialia, 2018
    Co-Authors: Jung Gi Kim, Kwanggeun Chin, Seung Mi Baek, Hak Hyeon Lee, Sunghak Lee, Hyoung Seop Kim
    Abstract:

    Abstract Deformation instabilities (i.e., yield point phenomenon (YPP) and serrated flow) were investigated for twinning-Induced Plasticity (TWIP) steel-core with low-carbon (LC) steel outer layer sheets. During tensile tests, both the YPP and serrated flow were suppressed as the volume fraction of the TWIP steel-core decreased. Electron backscattering diffraction analysis indicated that a strain gradient was Induced, and that geometrically necessary dislocations (GNDs) accumulated at the TWIP-LC steel interface. With increase in the dislocation density by plastic deformation, the deformation instabilities in the TWIP-cored layer steel sheets were suppressed due to the reduced probability of interaction of dislocation with carbon-solutes. This result indicates that the strain gradient at the interface of the layered sheets not only enhances the mechanical property, but also suppresses deformation instability.

  • stretchability and drawability of twinning Induced Plasticity steel cored layer steel sheets
    Journal of Materials Processing Technology, 2017
    Co-Authors: Jungsik Kim, Seung Mi Baek, Jae Ik Yoon, Minhong Seo, Won Tae Cho, K G Chin, See Am Lee, Hyoung Seop Kim
    Abstract:

    Abstracts In this work, the qualCONVERSION(0ities of sheet formability (i.e., stretchability and drawability), of twinning-Induced Plasticity (TWIP), steel-cored thr$ee-layer steel sheets were investigated in terms of tensile parameters (i.e., strain hardening exponent, strain rate sensitivity, normal anisotropy, mean R -value, and total elongation). The tensile parameters of TWIP steel-cored three-layer steel sheets follow the force-based rule of mixtures. The limit drawing ratio, the measure of drawability, of the three-layer steel sheet was proportional to the mean R -value and the strain rate sensitivity while the limit dome height (LDH), the measure of stretchability, could not be correlated with any tensile parameters. The LDH of the TWIP steel-cored layer sheet was superior to that of the single layer due to the inhibition of serration in the TWIP steel-core during the Erichsen test.

  • large deformation behavior of twin Induced Plasticity steels under high pressure torsion
    Metals and Materials International, 2016
    Co-Authors: Byung Ho Park, Sunghak Lee, Jung Gi Kim, Hu Young Jeong, Hyoung Seop Kim
    Abstract:

    A high-manganese twinning-Induced Plasticity (TWIP) steel is processed by high-pressure torsion (HPT) for up to 1 turn under 6 GPa pressure. The HPT-processed TWIP steels exhibit a homogeneous microstructure with a peak hardness of Hv 550. Deformation twinning is developed significantly in the early stage of the shear deformation, but is exhausted soon after 1/2 turn. The strength of the HPT-processed TWIP steel significantly increased due to the accumulation of dislocations, but elongation dramatically decreased due to a lack of dislocations available for plastic deformations. An analysis of the evolution of strength by imposed large strain under high pressure suggests that strain hardening due to dislocation and twinning is exhausted in the early stages of the HPT process. Further strategy for enhancing both strength and ductility is proposed.

  • austenite stability and heterogeneous deformation in fine grained transformation Induced Plasticity assisted steel
    Scripta Materialia, 2013
    Co-Authors: Joo Hyun Ryu, Hyoung Seop Kim, H K D H Bhadeshia, Jeong In Kim, Dongwoo Suh
    Abstract:

    We report the mechanistic explanation of the variation in Luders strain in fine- grained transformation-Induced Plasticity assisted steel. The austenite stability is demonstrated to have a profound influence on the Luders strain. Furthermore, it is shown unambiguously using a thermodynamic analysis that the transformation of austenite is strain-Induced. The work results in a generic method of distinguishing the cause of martensitic transformation during tensile tests, given that both stresses and strains are necessarily present beyond the yield point.

H K D H Bhadeshia - One of the best experts on this subject based on the ideXlab platform.

  • austenite stability and heterogeneous deformation in fine grained transformation Induced Plasticity assisted steel
    Scripta Materialia, 2013
    Co-Authors: Joo Hyun Ryu, Hyoung Seop Kim, H K D H Bhadeshia, Jeong In Kim, Dongwoo Suh
    Abstract:

    We report the mechanistic explanation of the variation in Luders strain in fine- grained transformation-Induced Plasticity assisted steel. The austenite stability is demonstrated to have a profound influence on the Luders strain. Furthermore, it is shown unambiguously using a thermodynamic analysis that the transformation of austenite is strain-Induced. The work results in a generic method of distinguishing the cause of martensitic transformation during tensile tests, given that both stresses and strains are necessarily present beyond the yield point.

  • medium alloy manganese rich transformation Induced Plasticity steels
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2013
    Co-Authors: Dongwoo Suh, H K D H Bhadeshia, Joo Hyun Ryu, Min Sung Joo, Hong Seok Yang, Kyooyoung Lee
    Abstract:

    The manganese concentration of steels which rely on transformation-Induced Plasticity is generally less than 2 wt pct. Recent work has highlighted the potential for strong and ductile alloys containing some 6 wt pct of manganese, but with aluminum additions in order to permit heat treatments which are amenable to rapid production. However, large concentrations of aluminum also cause difficulties during continuous casting. Alloy design calculations have been carried out in an effort to balance these conflicting requirements, while maintaining the amount of retained austenite and transformation kinetics. The results indicate that it is possible by adjusting the carbon and manganese concentrations to reduce the aluminum concentration, without compromising the mechanical properties or transformation kinetics. The deformation-Induced transformation of retained austenite is explained quantitatively, for a range of alloys, in terms of a driving force which takes into account the very fine state of the retained austenite.

  • transformation Induced Plasticity assisted steels stress or strain affected martensitic transformation
    Materials Science and Technology, 2007
    Co-Authors: S Chatterjee, H K D H Bhadeshia
    Abstract:

    AbstractTransformation Induced Plasticity (TRIP) assisted steels contain a small quantity of carbon enriched retained austenite, which transforms into martensite during the course of plastic deformation. Transformation of this kind can be Induced by both stress and plastic strain. The detailed mechanism by which the martensite is Induced is different for these two scenarios. An attempt is made here to discover the relative importance of these mechanisms and it is found that stress affected transformation can explain much of the variation in retained austenite content as a function of plastic strain.

Seokjae Lee - One of the best experts on this subject based on the ideXlab platform.