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Han, Jung-Hoon,Oh, Juhyun,Yoon, Sangmoon,Kim, Yanghoo,Han, Heung Nam,Kim, Miyoung Korean Society of Microscopy 2016 Applied microscopy Vol.46 No.4
Twinning-induced plasticity (TWIP) steels with the austenite structure containing high manganese exhibit both good strength and excellent formability. Such properties originate from crystallographic slip and mechanical twins produced when the austenite structure is under mechanical stress. There are 12 twin systems, referred to as twin variants, when slip is induced. These twin systems include twin planes and twin directions and play an important role in determining strength and ductility of the material by strongly influencing texture formation of the austenite structure. In the present study, twins produced in a high-Mn TWIP steel as a result of uniaxial tension were observed using a transmission electron microscope; a comparative analysis was performed through interaction energy calculations. Electron diffraction was used to determine the twin system with respect to the uniaxial tension direction in each grain. Both the Schmid factors and interacting energies required for the generation of twins were calculated and subsequently compared with experimental results. This approach demonstrated the possibility of predicting the deformation behavior of the material.
{10-12} 쌍정 특성이 AZ31 마그네슘 합금 압연재의 변형거동에 미치는 영향
박성혁(S. H. Park),홍성구(S. G. Hong),이종수(C. S. Lee) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.5
The active twin variants during {10-12} twinning of magnesium alloys were dependent on the activation mode (i.e., compression perpendicular to the c-axis or tension parallel to the c-axis) and their section mechanism was governed by the Schmid law. The activation of specific twin variants depending on the activation mode induced a significant difference in twinning characteristics, such as twin morphology, volume fraction of twins with strain, and twin texture, and consequently gave rise to a totally different effect on the deformation. The differences in the deformation characteristics (flow stress and strain hardening) between both activation modes were explained in relation with activation stresses for twinning and slips, activities of twinning and slips in the deformation, Hall-Petch effect by twinning-induced grain size change, and twinning-induced change in activities of slips.
Abnormal texture evolution of rolled Mg–3Al–1Zn alloy containing initial {10-12} twins
Lee, Jeong Hun,Park, Sung Hyuk,Hong, Seong-Gu,Won, Jong Woo,Lee, Chong Soo Elsevier 2015 Scripta materialia Vol.99 No.-
<P>The importance of initial {10-12} twins in the formation of deformation texture was investigated by conducting strain path change tests of rolled Mg–3Al–1Zn alloy in which {10-12} twinning dominated the deformation. The existence of initial twins changed a twinning process by preferring the growth of initial twins rather than the nucleation of new twins, which led to a non-Schmid behavior of twinning characteristics and consequently caused a completely different deformation texture compared with the counterpart without initial twins.</P>
Shin, E.J.,Jung, A.,Choi, S.H.,Rollett, A.D.,Park, S.S. Elsevier Sequoia 2012 Materials science & engineering. properties, micro Vol.538 No.-
A resolved shear stress (RSS) criterion and the microstructure-based-crystal plasticity finite element method (MB-CPFEM) were used to analyze the activation of twin variants in extruded AZ31 Mg alloys during ex situ uniaxial compression. The RSS criterion, which is simply based on the Schmid factor, failed to predict the activation of twin variants consisting of the second-highest RSS and the third-highest RSS. In contrast to the RSS criterion, the MB-CPFEM based on a quasi-3D finite element mesh successfully predicted the activation of twin variants consisting of the highest RSS and the second-highest RSS. The MB-CPFEM demonstrated that local fluctuation of the stress field induces the activation of twin variants with the second-highest RSS during uniaxial compression.
Choi, S.H.,Shin, E.J.,Seong, B.S. Elsevier Science 2007 Acta materialia Vol.55 No.12
To investigate deformation twins and the evolution of deformation texture during plastic deformation, uniaxial compression tests on a hot-rolled AZ31 Mg alloy were carried out at 200<SUP>o</SUP>C. Cylindrical specimens were then compressed in both the rolling and the normal directions. The findings revealed that texture evolution, work hardening and macroscopic anisotropy are strongly dependent on the loading direction. Electron backscattered diffraction analysis was used to examine the orientation of parent grains and twin bands in the AZ31 Mg alloy under uniaxial compression. A viscoplastic self-consistent model (VPSC) was theoretically employed to calculate the relative activities of slip and twin systems in polycrystalline hexagonal aggregates under uniaxial compression. Each deformed grain exhibited an independent number and type of twin variants under uniaxial compression. Neutron diffraction was used to measure the macroscopic texture of the AZ31 Mg alloy. The VPSC model was used to simulate texture evolution, work hardening and macroscopic anisotropy during the uniaxial compression. A modified predominant twin reorientation (PTR) scheme was suggested to explain the gradual increase in twin volume in deformed grains.
Singh, Jaiveer,Kim, Min-Seong,Choi, Shi-Hoon Elsevier 2019 International journal of plasticity Vol.117 No.-
<P><B>Abstract</B></P> <P>Micromechanical deformation behaviors of E-form fine grain (EFG), E-form coarse grain (ECG), and AZ31 magnesium (Mg) alloys were investigated and compared using a mini-V-bending test. EFG and ECG Mg alloys with a weaker texture showed better bendability compared with AZ31 alloy that has a stronger texture. The evolution of the microstructure and microtexture during the mini-V-bending process was experimentally analyzed via an electron back-scattered diffraction (EBSD) technique. This study was focused on the effect that deformation twinning exerts on the strain localization and crack initiation. The twin bands (TBs) developed in the tension zone of bent specimens found to be closely related to the strain localization and crack initiation during the mini-V-bending process. A resolved shear stress (RSS) criterion and microstructure based crystal plasticity finite element method (CPFEM) were used to theoretically predict the activation of { 10 1 ¯ 2 } tension (TTW) and { 10 1 ¯ 1 } compression (CTW) twins in Mg alloys under a mini-V-bending process. RSS analysis indicated that EFG and ECG Mg alloys are more favorable for the activity of TTW and less favorable for the activity of CTW when compared with AZ31 Mg alloy during a mini-V-bending process. However, RSS analysis was not effective in quantitatively predicting twin development. The relative activities of six deformation modes, accumulated twin fractions, and accumulated plastic strains were simulated via microstructure-based CPFEM modeling. Compared with RSS analysis, CPFEM precisely explained the twin behavior that has been experimentally observed in ECG and AZ31 Mg alloys.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effects of initial texture and grain size in Mg alloys under mini-V-bending tests were investigated. </LI> <LI> The micromechanical deformation behavior was studied using EBSD analysis, RSS criterion, and mesoscale CPFEM modeling. </LI> <LI> Deformation twinning was more prominent in ECG and EFG Mg alloys than in AZ31 Mg alloy during the mini-V-bending. </LI> <LI> In contrast to the RSS criterion, CPFEM modeling more accurately described the twin behavior observed in the experiments. </LI> <LI> The primary deformation mode in ECG and AZ31 Mg alloys was basal '> a and pyramidal '> c + a slip, respectively. </LI> </UL> </P>
Changfa Guo,Yue Xiao,Renlong Xin 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.9
In this work, we statistically investigate the texture effect on twinning behavior in rolling of an AZ31 Mg alloy by electronbackscatter diffraction technique and evaluate it by a generalized Schmid factor (GSF). The results show that twinningnucleation and area fraction are promoted significantly with the c-axis of grains rotating from the transverse direction to therolling direction. More importantly, twin propensity and the selection of twin variants can be well explained by the GSFthat is calculated based on an estimated stress state for rolling. The present results provide some insights into controlling themicrostructure and texture of Mg alloys by rolling processes.