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D L Chen - One of the best experts on this subject based on the ideXlab platform.
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influence of yttrium content on phase formation and Strain Hardening behavior of mg zn mn magnesium alloy
Journal of Alloys and Compounds, 2014Co-Authors: N Tahreen, Dingfei Zhang, Fusheng Pan, Xianquan Jiang, D L ChenAbstract:Abstract The aim of this study was to identify the effect of yttrium (Y) addition on the phase development and Strain Hardening behavior of an extruded Mg–Zn–Mn (ZM31) magnesium alloy. The addition of a small amount (0.3 wt.%) of Y in the alloy led to the formation of icosahedral quasicrystalline I (Mg3YZn6) phase. Both I-phase and W-phase (Mg3Y2Zn3) were present in the extruded ZM31+3.2Y alloy, while long period stacking ordered (LPSO) X-phase (Mg12YZn) and Mg24Y5 were observed in the extruded ZM31+6Y alloy. The Y addition significantly refined grains in the extruded state. The presence of I-phase in the extruded ZM31+0.3Y alloy increased hardness, compressive yield strength, and Stage B Strain Hardening Rate. The extruded ZM31+3.2Y alloy exhibited a lower hardness and Stage B Hardening Rate due to the formation of W-phase. Both extruded ZM31+0.3Y and ZM31+3.2Y alloys showed a yield point phenomenon with an initial negative Strain Hardening Rate. The extruded ZM31+6Y alloy had a high hardness and compressive yield strength without Stage B Hardening, suggesting a change of major deformation mode from twinning to slip mainly due to the role of LPSO X-phase. After solution treatment and aging, the hardness and compressive yield strength gradually increased with increasing Y content, while the Strain Hardening exponent and the extent of Stage B Strain Hardening decreased due to the dissolution of I- and W-phases and the presence of LPSO X-phase.
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detwinning and Strain Hardening of an extruded magnesium alloy during compression
Scripta Materialia, 2012Co-Authors: D Sarker, D L ChenAbstract:The plastic deformation of an extruded Mg–Al–Mn (AM30) magnesium alloy in the extrusion direction by compression can be characterized by three distinct stages. Twinning was observed in stage A with a decreasing Strain-Hardening Rate. Detwinning occurred due to strong twin–dislocation interactions in stage B, which was represented by an increasing Strain-Hardening Rate over an extended Strain range. Stage C with a decreasing Strain-Hardening Rate was due to a reducing resistance of fewer twins to the dislocation slip.
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tensile properties and Strain Hardening behavior of double sided arc welded and friction stir welded az31b magnesium alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010Co-Authors: S M Chowdhury, D L Chen, S D Bhole, X Cao, E Powidajko, D C Weckman, Y ZhouAbstract:Microstructures, tensile properties and work Hardening behavior of double-sided arc welded (DSAWed) and friction stir welded (FSWed) AZ31B-H24 magnesium alloy sheet were studied at different Strain Rates. While the yield strength was higher, both the ultimate tensile strength and ductility were lower in the FSWed samples than in the DSAWed samples due to welding defects present at the bottom surface in the FSWed samples. Strain-Hardening exponents were evaluated using the Hollomon relationship, the Ludwik equation and a modified equation. After welding, the Strain-Hardening exponents were nearly twice that of the base metal. The DSAWed samples exhibited stronger Strain-Hardening capacity due to the larger grain size coupled with the divorced eutectic structure containing -Mg17Al12 particles in the fusion zone, compared to the FSWed samples and base metal. Kocks-Mecking type plots were used to show Strain-Hardening stages. Stage III Hardening occurred after yielding in both the base metal and the welded samples. At lower Strains a higher Strain-Hardening Rate was observed in the base metal, but it decreased rapidly with increasing net flow stress. At higher Strains the Strain-Hardening Rate of the welded samples became higher, because the recrystallized grains in the FSWed and the larger re-solidified grains coupled with particles in the DSAWed provided more space to accommodate dislocation multiplication during plastic deformation. The Strain-Rate sensitivity evaluated via Lindholm's approach was observed to be higher in the base metal than in the welded samples. © 2010 Elsevier B.V. All rights reserved.
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Strain Hardening and Strain Rate sensitivity of an extruded magnesium alloy
Journal of Materials Engineering and Performance, 2008Co-Authors: D L ChenAbstract:The Strain-Hardening behavior and Strain-Rate sensitivity of an extruded AZ31B magnesium alloy were determined at different Strain Rates between 10−2 and 10−5 s−1 in relation to the thickness of specimens (2.5 and 4.5 mm). Both the common approach and Lindholm’s approach were used to evaluate the Strain-Rate sensitivity. The yield strength (YS) and the ultimate tensile strength (UTS) increased, the ductility decreased, and the brittle fracture characteristics increased with increasing Strain Rate. The thinner specimens exhibited a slightly higher UTS, lower ductility, higher Strain-Hardening exponent, and Strain-Hardening Rate due to smaller grain sizes. The stage III Strain-Hardening Rate linearly decreased with increasing true stress, but increased with increasing Strain Rate. In comparison to the common approach, the Lindholm’s approach was observed to be more sensitive in characterizing the Strain-Rate sensitivity due to larger values obtained. The thinner specimens also exhibited higher Strain-Rate sensitivity. As the true Strain increased, the Strain-Rate sensitivity decreased.
Young-kook Lee - One of the best experts on this subject based on the ideXlab platform.
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effect of grain misorientation angle on twinning propagation in ti 15mo alloy
Metals and Materials International, 2018Co-Authors: Young-kook Lee, Kuk Hyun SongAbstract:This study was carried out to evaluate the effect of grain misorientation angle distribution on the deformation behavior and twinning of Ti–15Mo alloy. Cold rolling exhibited a significant texture with grains oriented along the {111}//normal direction, which correlate with a higher fraction of low-angle boundaries. This material showed a lower yield strength and higher elongation than those of the hot rolled material. The twinning propagation mainly occurred between neighboring grains with a low-angle relation. Consequently, the texture development was correlated with low-angle boundaries and affected by the increase in the twinning density, which increased the Strain Hardening Rate.
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effect of grain size on tensile properties of fine grained metastable β titanium alloys fabricated by stress induced martensite and its reverse transformations
Scripta Materialia, 2012Co-Authors: Minghui Cai, Chanyoung Lee, Young-kook LeeAbstract:Fine-grained Ti–16V–3.5Al–3Sn alloys were fabricated through the stress-induced martensite and its reverse transformations. All tensile curves of the alloys showed double yielding, high Strain Hardening and low trigger stress for martensitic transformation. As the grain size increased, the trigger stress decreased and then increased again, while the dimples on the fractured surface became large and non-uniform. The three-stage Strain Hardening and high Strain-Hardening Rate were closely associated with the stress-induced β to α″ martensitic transformation and dislocation Hardening.
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Strain Hardening behavior of a fe 18mn 0 6c 1 5al twip steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: Jae Eun Jin, Young-kook LeeAbstract:Abstract The Strain Hardening behavior of a Fe–18Mn–0.6C–1.5Al TWIP steel was investigated through the modified Crussard–Jaoul (C–J) analysis and microstructural observations. The Strain Hardening Rate obtained by modified C–J analysis was high up to the critical Strain of 37% and then greatly decreased with further Strain. The electron backscatter diffraction (EBSD) observation showed that the deformation twinning Rate is greatly decreased beyond about 34% Strain, indicating that the reduced Strain Hardening Rate at the large Strain region is attributed to the deceleration of deformation twinning Rate. The volume fraction of twinned region was increased with tensile Strain due to the increase in the number of deformation twins not to the lateral growth of each deformation twin.
Seok Su Sohn - One of the best experts on this subject based on the ideXlab platform.
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effect of tempering conditions on adiabatic shear banding during dynamic compression and ballistic impact tests of ultra high strength armor steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2020Co-Authors: Selim Kim, Seok Su Sohn, Dongwoo Suh, Sung Suk Hong, Hong Kyu Kim, Sunghak LeeAbstract:Abstract In this study, roles of Strain-Hardening Rate on susceptibility of adiabatic shear band (ASB) formation and subsequent cracking were investigated in two ultra-high-strength armor steel plates heat-treated differently. The quenched and tempered steel contained ~2% of retained austenite in the tempered martensitic matrix, while the quenched and austempered steel contained ~4% retained austenite in the bainitic matrix partly with the tempered martensite. The actual ballistic impact test results revealed the lower sensitivity of ASB formation in the austempered steel than in the tempered steel, which corresponded well to the higher critical Strain for ASB formation in the dynamic compressive test using a laboratory-scale split Hopkinson pressure bar (SHPB). The austempered steel caused the higher internal stress among various constituents, and all the retained austenite transformed into martensite during the deformation, thereby leading to transformation-induced plasticity (TRIP) effect. The higher Strain-Hardening Rate induced by these higher internal stress and TRIP effect increased resistance to ASB formation, which was confirmed by a calculation of ASB susceptibility. Thus, the austempered steel was much less susceptible to the ASB formation during the ultra-high-speed deformation. Consequently, the increased resistance to ASB formation retarded the initiation and propagation of ASBs and cracks.
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Interpretation of dynamic tensile behavior by austenite stability in ferrite-austenite duplex lightweight steels
'Springer Science and Business Media LLC', 2018Co-Authors: Jaeyeong Par, Seok Su Sohn, Hyeok Jae Jeong, Jai-hyun Kwa, Kim, Hyoung Seop, Sunghak LeeAbstract:Phenomena occurring in duplex lightweight steels under dynamic loading are hardly investigated, although its understanding is essentially needed in applications of automotive steels. In this study, quasi-static and dynamic tensile properties of duplex lightweight steels were investigated by focusing on how TRIP and TWIP mechanisms were varied under the quasi-static and dynamic loading conditions. As the annealing temperature increased, the grain size and volume fraction of austenite increased, thereby gradually decreasing austenite stability. The Strain-Hardening Rate curves displayed a multiple-stage Strain-Hardening behavior, which was closely related with deformation mechanisms. Under the dynamic loading, the temperature rise due to adiabatic heating raised the austenite stability, which resulted in the reduction in the TRIP amount. Though the 950 degrees C-annealed specimen having the lowest austenite stability showed the very low ductility and strength under the quasi-static loading, it exhibited the tensile elongation up to 54% as well as high Strain-Hardening Rate and tensile strength (1038 MPa) due to appropriate austenite stability under dynamic loading. Since dynamic properties of the present duplex lightweight steels show the excellent strength-ductility combination as well as continuously high Strain Hardening, they can be sufficiently applied to automotive steel sheets demanded for stronger vehicle bodies and safety enhancement.
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achievement of high yield strength and Strain Hardening Rate by forming fine ferrite and dislocation substructures in duplex lightweight steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Hyejin Song, Seok Su SohnAbstract:Abstract Lightweight steels containing a considerable content of Al show high specific strength and ductility, but there are some drawbacks such as low yield strength and stringer-type bands formed along the rolling direction. Here we design new duplex lightweight steel in order to complement the drawbacks, and achieve ultra-high yield strength (865 MPa), good ductility (41%). Submicron ferrite mainly affects high yield-to-tensile ratio, and high Strain Hardening is attributed to Lomer-Cottrell lock and planar slip, and cell structure by further deformation in austenite. These results are expected to provide a desirable possibility for applications to reinforcement components requiring high yield-to-tensile ratio.
Fereshteh Ebrahimi - One of the best experts on this subject based on the ideXlab platform.
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effect of stacking fault energy on plastic deformation of nanocrystalline face centered cubic metals
Applied Physics Letters, 2004Co-Authors: Fereshteh Ebrahimi, Z AhmedAbstract:The effect of stacking fault energy (SFE) on the tensile stress–Strain behavior of nanocrystalline face-centered cubic (fcc) metals was investigated. The stacking fault energy of nickel was decreased by alloying with copper or iron. It was found that, as predicted by a recent simulation study, decreasing the SFE increases the Strain Hardening Rate of the nanocrystalline fcc metals. The effect was more pronounced in the nickel–copper alloy, which had a smaller average grain size.
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transition of deformation and fracture behaviors in nanostructured face centered cubic metals
Applied Physics Letters, 2004Co-Authors: Hongqi Li, Fereshteh EbrahimiAbstract:Tensile stress–Strain curves demonstRate that single-phase nanocrystalline face-centered-cubic (fcc) metals are intrinsically ductile and their failure begins with necking. However, the area reductions and the fracture behaviors were found to be dependent on the grain size. When plastic deformation is governed by dislocation activity, the nanocrystalline samples behave similar to the conventional coarse-grained materials. As the grain size is reduced to the regime where grain boundary sliding dominates, the material shows very high Strain-Hardening Rate and the tensile samples fail by microcracking with no noticeable reduction in area.
Chaoyue Zhao - One of the best experts on this subject based on the ideXlab platform.
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Strain Hardening of as extruded mg xzn x 1 2 3 and 4 wt alloys
Journal of Materials Science & Technology, 2019Co-Authors: Chaoyue Zhao, Teng Tu, Xianhua Chen, Jingfeng Wang, Andrej AtrensAbstract:The influence of Zn on the Strain Hardening of as-extruded Mg-xZn (x = 1, 2, 3 and 4 wt%) magnesium alloys was investigated using uniaxial tensile tests at 10 s at room temperature. The Strain Hardening Rate, the Strain Hardening exponent and the Hardening capacity were obtained from true plastic stress-Strain curves. There were almost no second phases in the as-extruded Mg-Zn magnesium alloys. Average grain sizes of the four as-extruded alloys were about 17.8 μm. With increasing Zn content from 1 to 4 wt%, the Strain Hardening Rate increased from 2850 MPa to 6810 MPa at (σ-σ) = 60 MPa, the Strain Hardening exponent n increased from 0.160 to 0.203, and the Hardening capacity, Hc increased from 1.17 to 2.34. The difference in Strain Hardening response of these Mg-Zn alloys might be mainly caused by weaker basal texture and more solute atoms in the α-Mg matrix with higher Zn content.
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Effect of Sn content on Strain Hardening behavior of as-extruded Mg-Sn alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Chaoyue Zhao, Xianhua Chen, Di ZhaoAbstract:Abstract The effects of Sn content on Strain Hardening behavior of as-extruded Mg-xSn (x = 1.3, 2.4, 3.6 and 4.7 wt%) binary alloys were investigated by uniaxial tensile tests at room temperature. Strain Hardening Rate, Strain Hardening exponent and Hardening capacity were obtained from the true plastic stress-Strain curves. After hot extrusion, the as-extruded Mg-Sn alloys are mainly composed of α-Mg matrix and second phase Mg2Sn, which only exists in Mg-3Sn and Mg-4Sn. Average grain size decreases from 15.6 μm to 3.6 µm with Sn content increases from 1.3 to 4.7 wt%. The experimental results show that Sn content decreases Strain Hardening ability of as-extruded Mg-Sn alloys, but gives rise to an obvious elevation in tensile strength, yield strength and elongation of them. With increasing Sn content, Strain Hardening Rate decreases from 3527 MPa to 1211 MPa at (σ-σ0.2) = 50 MPa, Strain Hardening exponent decreases from 0.21 to 0.13 and Hardening capacity decreases from 1.66 to 0.63. The variation in Strain Hardening behavior of Mg-Sn alloys with Sn content is discussed in terms of the influences of grain size and distribution of grain orientation.