The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Chongxiang Huang - One of the best experts on this subject based on the ideXlab platform.
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synergetic deformation induced extraordinary softening and hardening in gradient copper
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2019Co-Authors: Yanfei Wang, Mingsai Wang, Aihui Huang, Qiong He, Linyun Song, Yusheng Li, Chongxiang HuangAbstract:Abstract A gradient-structured Cu sample composed of grain-size gradient surface layer (GSL) and homogeneous coarse-grained (CG) core was fabricated by surface severe plastic deformation. Microhardness measurements revealed that both tension-induced softening in the top nanograined surface layer and hardening in the subsurface layer of integrated gradient sample were far more pronounced than that of a freestanding GSL, i.e. extraordinary softening and hardening occurred in gradient sample. The synergetic deformation between GSL and CG core produced accumulation of geometrically necessary dislocations and thereby Back Stress strengthening, resulting in extra flow Stress and hardening. The extraordinary softening was attributed to the extra flow Stress-assisted grain coarsening in nanograined layer. Furthermore, strain measurements proved that the CG matrix plays critical roles in stabilizing the grain coarsening and homogenizing the strain distribution in nanograined layer, which were favorable for the uniform ductility.
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interface affected zone for optimal strength and ductility in heterogeneous laminate
Materials Today, 2018Co-Authors: Chongxiang Huang, Y F Wang, Heinz Werner Hoppel, Mathias Goken, Xiaolei WuAbstract:Interfaces have been reported to significantly strengthen and toughen metallic materials. However, there has been a long-standing question on whether interface-affected-zone (IAZ) exists, and how it might behave. Here we report in situ high-resolution strain mapping near interfaces in a copper–bronze heterogeneous laminate, which revealed the existence of IAZs. Defined as the zone with strain gradient, the IAZ was found to form by the dislocations emitted from the interface. The IAZ width remained largely constant with a magnitude of a few micrometers with increasing applied strain. Interfaces produced both Back Stress strengthening and work hardening, which led to both higher strength and higher ductility with decreasing interface spacing until adjacent IAZs started to overlap, after which a tradeoff between strength and ductility occurred, indicating the existence of an optimum interface spacing for the best mechanical properties. These findings are expected to help with designing laminates and other heterogeneous metals and alloys for superior mechanical properties.
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improved Back Stress and synergetic strain hardening in coarse grain nanostructure laminates
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Y F Wang, Muxin Yang, Mingsai Wang, Kun Yin, Aihui Huang, Chongxiang HuangAbstract:Abstract The effect of Back Stress on the mechanical behaviors of heterogeneous material is studied in two modeled heterogeneous laminates, i.e. laminated structure with a nanostructured (NS) Cu-Zn alloy layer sandwiched between two coarse-grained (CG) pure Cu layers. The improved tensile ductility of NS layer is revealed and attributed to the constraint from the stable CG layers. It is found that the elastic/plastic interaction between NS and CG layers is capable of significantly improving the Back Stress, which makes a significant contribution to the synergetic strain hardening in low strain stage. Furthermore, a higher mechanical incompatibility permits stronger and longer mutual interaction between layers, i.e. coupling effect, which contributes to a higher Back Stress. These results improve our understanding about the role of Back Stress on mechanical behaviors of heterogeneous laminate materials.
Fuping Yuan - One of the best experts on this subject based on the ideXlab platform.
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Back Stress induced strengthening and strain hardening in dual phase steel
Materialia, 2019Co-Authors: Fuping Yuan, Xun Liu, Qiqi Xue, Wei Wang, L L Zhou, Ping Jiang, Y G WeiAbstract:Abstract Strain hardening for ductility remains challenging especially at high yield strength when dislocation plasticity is usually invalid. The hetero-deformation provides an effective route to induce extra Back Stress hardening specifically in hetero-structures inherently with large mismatch of mechanical responses, e.g. flow Stress and strain hardening etc., upon applied loading. In this paper, both strengthening and strain hardening were investigated in a dual- phase steel, consisting of ductile γ-austenite and almost non-deformable B2 intermetallic phase as the second phase of volume fraction of 23%. The chemical composition was 0.86C, 16Mn, 10Al, 5Ni, balance Fe (wt.%). Of special note is two distinct hetero-deformation responses during both tensile and interrupted unload-reload testing. One is the yield-drop, while the other is hysteresis loop. Both unceasingly appear even from the elasto-plastic yield stage up to whole uniform deformation. The measured Back Stress and resultant Back Stress hardening account for a large proportion of global flow Stress and strain hardening. Further, both Schmid factor and Kernel average misorientation (KAM) values were measured after tensile deformation. Un-expected, only γ-grains bordering on B2-phase show a significant decrease in the average Schmid factor, relative to almost unchanged in left γ-grains still next to γ-ones as well as B2-phase. This indicates that γ-grains adjacent to B2-phase bear the vast majority of plastic strains, not simple strain partitioning between γ and B2. Because of this, from the onset of yielding to end of tensile deformation, those γ-grains, in contrast to left γ-grains and B2 phase, exhibit a maximal increment in KAM values. This serves as a solid evidence of the generation of geometrically necessary dislocations to accommodate strain gradient near γ/B2 phase boundaries. It turns out that hetero-deformation due to plastic incompatibility induces the operation of Back Stresses, leading to both strengthening and strain hardening as well. Finally, a microstructure-based model was developed to calculate Back Stress which was well consistent with experimentally measured Back Stress.
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strain hardening behaviors and strain rate sensitivity of gradient grained fe under compression over a wide range of strain rates
Mechanics of Materials, 2016Co-Authors: Fuping Yuan, Ping Chen, Yanpeng Feng, Ping JiangAbstract:In the present work, gradient-grained Fe was synthesized by means of surface mechanical grinding treatment, and then the compression behaviors of the coarse-grained Fe and the gradient-grained Fe were investigated under both quasi-static and dynamic loading conditions over a wide range of strain rates (from 5 x 10(-4) to 10(4) s(-1)). After surface mechanical grinding treatment, equiaxed ultrafine grains, elongated lamellar ultrafine grains, full-developed sub-grains with dense dislocations walls, non-fully-developed dislocation cells, and deformed coarse grains are sequentially observed along the depth from the treated surface. The grain/cell size increases while the measured micro-hardness decreases along the depth for the gradient-grained Fe. The gradient-grained structure shows apparent strain hardening behaviors at all strain rates up to 10(4) s(-1) although the strain hardening exponent (n) for the gradient-grained Fe is smaller than that of the coarse-grained Fe at the same strain rate. This apparent hardening behavior is attributed to the hardening from both the coarse-grained center and the surface gradient layers when the strain localization trend for the ultrafine-grained surface layers is suppressed by the coarse-grained center. The extra hardening might be due to the Back Stress hardening associated with the constraint and mechanical incompatibility between different layers in the gradient-grained structure. The dynamic strain rate sensitivity of the gradient-grained Fe is observed to be slightly larger than that of the coarse-grained Fe, which is controversial to the general observation that strain rate sensitivity should decrease with reduction of grain size for BCC metals. The geometrically necessary dislocations associated with the Back Stress hardening and the grain size gradient result in additional increase in dislocation density, which may be the reason for the enhanced dynamic strain rate sensitivity in the gradient-grained Fe even it has smaller average grain size compared to the coarse-grained Fe. The present results should provide insights for the applications of gradient-grained structure under dynamic conditions. (C) 2016 Elsevier Ltd. All rights reserved.
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Back Stress strengthening and strain hardening in gradient structure
Materials research letters, 2016Co-Authors: Muxin Yang, Fuping Yuan, Xiaolei WuAbstract:We report significant Back Stress strengthening and strain hardening in gradient structured (GS) interstitial-free (IF) steel. Back Stress is long-range Stress caused by the pileup of geometrically necessary dislocations (GNDs). A simple equation and a procedure are developed to calculate Back Stress basing on its formation physics from the tensile unloading–reloading hysteresis loop. The gradient structure has mechanical incompatibility due to its grain size gradient. This induces strain gradient, which needs to be accommodated by GNDs. Back Stress not only raises the yield strength but also significantly enhances strain hardening to increase the ductility.Impact Statement: Gradient structure leads to high Back Stress hardening to increase strength and ductility. A physically sound equation is derived to calculate the Back Stress from an unloading/reloading hysteresis loop.
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heterogeneous lamella structure unites ultrafine grain strength with coarse grain ductility
Proceedings of the National Academy of Sciences of the United States of America, 2015Co-Authors: Muxin Yang, Fuping Yuan, Y T Zhu, Yujie Wei, Xiaoxu HuangAbstract:Grain refinement can make conventional metals several times stronger, but this comes at dramatic loss of ductility. Here we report a heterogeneous lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse-grained metal. It also has higher strain hardening than coarse-grained Ti, which was hitherto believed impossible. The heterogeneous lamella structure is characterized with soft micrograined lamellae embedded in hard ultrafine-grained lamella matrix. The unusual high strength is obtained with the assistance of high Back Stress developed from heterogeneous yielding, whereas the high ductility is attributed to Back-Stress hardening and dislocation hardening. The process discovered here is amenable to large-scale industrial production at low cost, and might be applicable to other metal systems.
Muxin Yang - One of the best experts on this subject based on the ideXlab platform.
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improved Back Stress and synergetic strain hardening in coarse grain nanostructure laminates
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Y F Wang, Muxin Yang, Mingsai Wang, Kun Yin, Aihui Huang, Chongxiang HuangAbstract:Abstract The effect of Back Stress on the mechanical behaviors of heterogeneous material is studied in two modeled heterogeneous laminates, i.e. laminated structure with a nanostructured (NS) Cu-Zn alloy layer sandwiched between two coarse-grained (CG) pure Cu layers. The improved tensile ductility of NS layer is revealed and attributed to the constraint from the stable CG layers. It is found that the elastic/plastic interaction between NS and CG layers is capable of significantly improving the Back Stress, which makes a significant contribution to the synergetic strain hardening in low strain stage. Furthermore, a higher mechanical incompatibility permits stronger and longer mutual interaction between layers, i.e. coupling effect, which contributes to a higher Back Stress. These results improve our understanding about the role of Back Stress on mechanical behaviors of heterogeneous laminate materials.
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Back Stress strengthening and strain hardening in gradient structure
Materials research letters, 2016Co-Authors: Muxin Yang, Fuping Yuan, Xiaolei WuAbstract:We report significant Back Stress strengthening and strain hardening in gradient structured (GS) interstitial-free (IF) steel. Back Stress is long-range Stress caused by the pileup of geometrically necessary dislocations (GNDs). A simple equation and a procedure are developed to calculate Back Stress basing on its formation physics from the tensile unloading–reloading hysteresis loop. The gradient structure has mechanical incompatibility due to its grain size gradient. This induces strain gradient, which needs to be accommodated by GNDs. Back Stress not only raises the yield strength but also significantly enhances strain hardening to increase the ductility.Impact Statement: Gradient structure leads to high Back Stress hardening to increase strength and ductility. A physically sound equation is derived to calculate the Back Stress from an unloading/reloading hysteresis loop.
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heterogeneous lamella structure unites ultrafine grain strength with coarse grain ductility
Proceedings of the National Academy of Sciences of the United States of America, 2015Co-Authors: Muxin Yang, Fuping Yuan, Y T Zhu, Yujie Wei, Xiaoxu HuangAbstract:Grain refinement can make conventional metals several times stronger, but this comes at dramatic loss of ductility. Here we report a heterogeneous lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse-grained metal. It also has higher strain hardening than coarse-grained Ti, which was hitherto believed impossible. The heterogeneous lamella structure is characterized with soft micrograined lamellae embedded in hard ultrafine-grained lamella matrix. The unusual high strength is obtained with the assistance of high Back Stress developed from heterogeneous yielding, whereas the high ductility is attributed to Back-Stress hardening and dislocation hardening. The process discovered here is amenable to large-scale industrial production at low cost, and might be applicable to other metal systems.
Y T Zhu - One of the best experts on this subject based on the ideXlab platform.
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bauschinger effect and Back Stress in gradient cu ge alloy
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2017Co-Authors: Shenbao Jin, Hao Zhou, Zhe Yin, Jian Yang, Yulan Gong, Y T Zhu, Gang Sha, Xinkun ZhuAbstract:Using surface mechanical attrition treatment (SMAT), a gradient structure composed of two gradient structure (GS) layers and a coarse grain (CG) layer was generated from a Cu-5.7 wt pct Ge alloy, significantly improving the yield strength of the sample. Unloading–reloading tests showed an unusual Bauschinger effect in these GS samples. The Back Stresses caused by the accumulated geometrically necessary dislocations (GNDs) on the GS/CG border increased with increasing strain. As found by electron Backscatter diffraction (EBSD), the GNDs are mainly distributed in the gradient structured layer, and the density of the GNDs increase with increasing SMAT time. The effect of the Back Stress increased with increasing SMAT processing time due to the increase in the strain gradient. The pronounced Bauschinger effect in a GS sample can improve the resistance to forward plastic flow and finally contributes to the high strength of GS samples.
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heterogeneous lamella structure unites ultrafine grain strength with coarse grain ductility
Proceedings of the National Academy of Sciences of the United States of America, 2015Co-Authors: Muxin Yang, Fuping Yuan, Y T Zhu, Yujie Wei, Xiaoxu HuangAbstract:Grain refinement can make conventional metals several times stronger, but this comes at dramatic loss of ductility. Here we report a heterogeneous lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse-grained metal. It also has higher strain hardening than coarse-grained Ti, which was hitherto believed impossible. The heterogeneous lamella structure is characterized with soft micrograined lamellae embedded in hard ultrafine-grained lamella matrix. The unusual high strength is obtained with the assistance of high Back Stress developed from heterogeneous yielding, whereas the high ductility is attributed to Back-Stress hardening and dislocation hardening. The process discovered here is amenable to large-scale industrial production at low cost, and might be applicable to other metal systems.
Xiaolei Wu - One of the best experts on this subject based on the ideXlab platform.
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perspective on hetero deformation induced hdi hardening and Back Stress
Materials research letters, 2019Co-Authors: Xiaolei WuAbstract:Heterostructured materials have been reported as a new class of materials with superior mechanical properties, which was attributed to the development of Back Stress. There are numerous reports on ...
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interface affected zone for optimal strength and ductility in heterogeneous laminate
Materials Today, 2018Co-Authors: Chongxiang Huang, Y F Wang, Heinz Werner Hoppel, Mathias Goken, Xiaolei WuAbstract:Interfaces have been reported to significantly strengthen and toughen metallic materials. However, there has been a long-standing question on whether interface-affected-zone (IAZ) exists, and how it might behave. Here we report in situ high-resolution strain mapping near interfaces in a copper–bronze heterogeneous laminate, which revealed the existence of IAZs. Defined as the zone with strain gradient, the IAZ was found to form by the dislocations emitted from the interface. The IAZ width remained largely constant with a magnitude of a few micrometers with increasing applied strain. Interfaces produced both Back Stress strengthening and work hardening, which led to both higher strength and higher ductility with decreasing interface spacing until adjacent IAZs started to overlap, after which a tradeoff between strength and ductility occurred, indicating the existence of an optimum interface spacing for the best mechanical properties. These findings are expected to help with designing laminates and other heterogeneous metals and alloys for superior mechanical properties.
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Back Stress strengthening and strain hardening in gradient structure
Materials research letters, 2016Co-Authors: Muxin Yang, Fuping Yuan, Xiaolei WuAbstract:We report significant Back Stress strengthening and strain hardening in gradient structured (GS) interstitial-free (IF) steel. Back Stress is long-range Stress caused by the pileup of geometrically necessary dislocations (GNDs). A simple equation and a procedure are developed to calculate Back Stress basing on its formation physics from the tensile unloading–reloading hysteresis loop. The gradient structure has mechanical incompatibility due to its grain size gradient. This induces strain gradient, which needs to be accommodated by GNDs. Back Stress not only raises the yield strength but also significantly enhances strain hardening to increase the ductility.Impact Statement: Gradient structure leads to high Back Stress hardening to increase strength and ductility. A physically sound equation is derived to calculate the Back Stress from an unloading/reloading hysteresis loop.