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Positive Strain Rate Sensitivity and Deformation Behavior of a Fe–29Mn–3Al–3Si TWIP Steel

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Acta Metallurgica Sinica(English Letters) 2022年第11期35卷 1825-1836页

作者： Shucheng Shen cuilan wu Pan Xie Yuanrui Liu Center of High Resolution Electron Microscopy College of Materials Science and EngineeringHunan UniversityChangsha 410082China

The Fe-29 Mn-3 Al-3 Si twin-induced plasticity(TWIP)steel is used to conduct quasi-static compression and dynamic impact deformation with strain rates ranging from 8.3×10^(-4) to 3800 s^(-1).The microstructures and properties of deformed samples under different strain rates were investigated *** results show that positive strain rate sensitivity was observed with the increase in strain rates and that there was a significant difference in strain rate sensitivity factor(m)between quasi-static compression(m=0.029)and dynamic impact deformation(m=0.190).Compared to the quasi-static compression,the dynamic impact deformation exhibited higher yield *** examination reveals that the primary twins were frequently found during the quasi-static compression process,and the secondary twins were rarely ***,the secondary and multi-fold deformation twins were florescent in the dynamic impact *** the initial stage of dynamic impact deformation,partial dislocations and staking faults on multiple conjugate{111}planes were simultaneously activated and produced a large number of Lomer-Cottrell dislocations,resulting in a large increase in yield strength during dynamic impact.

关键词： TWIP steel Dynamic deformation Strain rate sensitivity Multi-fold deformation twins

Dislocation-Induced Precipitation and Its Strengthening of Al–Cu–Li–Mg Alloys with High Mg

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Acta Metallurgica Sinica(English Letters) 2021年第5期34卷 597-605页

作者： Xiangpeng Gong Shifang Luo Shiyong Li cuilan wu Center for High-Resolution Electron Microscopy College of Materials Science and EngineeringHunan UniversityChangsha410082China

Generally, the good combination of pre-deformation and aging can improve the mechanical strength of the Al–Cu–Li–Mg alloys. However, the effects of pre-deformation on competitive precipitation relationship and precipitation strengthening have not been clarified in detail in Al–Cu–Li–Mg alloys with high Mg. In the present study, the effects of pre-deformation level on the microstructure and mechanical properties of an Al–2.95 Cu–1.55 Li–0.57 Mg–0.18 Zr alloy have been investigated. It is found that the introduction of dislocation by 5% pre-deformation can facilitate the precipitation of new successive composite precipitates and T _1 precipitates along the sub-grain boundaries or dislocations and inhibit the precipitation of dispersive GPB zones which is the main precipitates of the alloys without pre-deformation. The introduction of 5% pre-deformation can enhance the mechanical properties considerably. When the pre-deformation level increases from 5 to 15%, the number density of the successive composite precipitates and T _1 precipitates increases, and the aspect ratio of T _1 precipitates decreases. The decrease in T _1 precipitate aspect ratio and the increment of the successive composite precipitates result in the reduction in precipitation strengthening. Therefore, the increase in pre-deformation level from 5 to 15% does not further improve the mechanical properties of the alloys, although the dislocation strengthening increases continuously.

关键词： Aluminum alloys Precipitation behavior Pre-deformation Precipitation strengthening Dislocation strengthening

BOUNDEDNESS OF COMMUTATORS FOR MARCINKIEWICZ INTEGRALS ON WEIGHTED HERZ-TYPE HARDY SPACES

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Analysis in Theory and Applications 2011年第4期27卷 365-376页

作者： cuilan wu Xuzhou Normal University China

In this paper, the authors study the boundedness of the operator μ^bΩ, the commutator generated by a function b ∈Lipβ （R^n）（0 〈β 〈 1） and the Marcinkiewicz integral μΩ on weighted Herz-type Hardy spaces.

关键词： Marcinkiewicz integral commutator weighted Herz space Hardy space

An Electron Microscopy Study of Vein-like Grain Boundary Microstructure in Nitrocarburized Low Carbon Steels

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Journal of Materials Science & Technology 2013年第7期29卷 669-672页

作者： Wanglin Chen cuilan wu Jianghua Chen Aigui He Center of High Resolution Electron Microscopy College of Materials Science and EngineeringHunan University

The coarsened grain boundaries （GBs） with vein-like morphology frequently appear in the nitrogen diffusion layer of nitrocarburized carbon steels. The electron probe X-ray microanalysis shows that such vein-like GBs are rich in nitrogen and carbon atoms. Transmission electron microscopy and scanning electron microscopy further reveal that the coarsened GBs consist of γ＇-nitrocarbide （Fe4（C,N）） and ε-nitrocarbide lamellas that are formed during nitrocarburizing due to high nitrogen concentration at GBs. It is shown that many of {111}〈112〉 micro twins exist in the γ＇-phase lamellas and thin ε-phase slices prefer to nucleate at their twin boundaries with the orientation relationship of {0001}ε//{111}γ＇. Upon growing large γ＇-Iamellas may become faceted and thin ε-Iamellas may grow thicker and become the main portions in the vein-like GBs. The microstructure evolution occurring in the vein-like GBs can be depicted as： α ＋ [N]/[C] → ＋ [C,N] →ε-nitrocarbides.

关键词： Nitrocarburizing Grain boundary γ'-Fe4(C,N) e-Nitrocarbide

Unusual relationship between impact toughness and grain size in a high-manganese steel

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Journal of Materials Science & Technology 2021年第30期89卷 122-132页

作者： Pan Xie Shucheng Shen cuilan wu Jiehua Li Jianghua Chen Center for High Resolution Electron Microscopy College of Materials Science and EngineeringHunan UniversityChangsha410082China Institute of Casting Research Montanuniversität LeobenA-8700LeobenAustria

The high-manganese steels are important structural materials,owing to their excellent toughness at low ***,the microstructural causes for their unusual properties have not adequately been understood thus ***,we report a reversal relationship between impact toughness and grain size in a high-manganese steel and its unrevealed microscopic mechanisms,which result in an excellent low-temperature toughness of the *** investigations show that with increasing grain size the impact toughness of the steel can be improved drastically,especially at *** electron microscopy characterization reveals that the enhanced impact toughness of the coarse-grained steel is attributed to the twinning induced plasticity and transformation induced plasticity effects,which produce large quantities of deformation twins,ε_(hcp)-martensite andα'_(bcc)-***,in the fine-grained steels,the formation of deformation twins and martensite is significantly inhibited,leading to the decrease of impact *** characterizations also indicate thatε_(hcp)-martensite becomes more stable thanα'_(bcc)-martensite with decreasing temperature,resulting in characteristic microstructures in the coarse-grained samples after impact deformation at liquid nitrogen *** the coarse-grained samples under impact deformation at-80℃,ε_(hcp)-martensite transformation,α'_(bcc)-martensite transformation and deformation twinning all occur simultaneously,which greatly improves the toughness of the steel.

关键词： Toughness Grain size Twinning induced plasticity Transformations induced plasticity High-manganese steel

Boundedness of Some Commutators of Marcinkiewicz Integrals on Hardy Spaces

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Analysis in Theory and Applications 2023年第1期39卷 16-27页

作者： cuilan wu School of Mathematics and Statistics Jiangsu Normal UniversityXuzhouJiangsu 221116China

Based on the results of the boundedness ofµ^(b)_(Ω)on L^(p) spaces,by using the theory of atomic decomposition of Hardy spaces,we obtain the boundedness ofµ^(b)_(Ω)on Hardy spaces.

关键词： Marcinkiewicz integral commutator Lipschitz space Hardy space

Improved Properties in Relation to Fine Precipitate Microstructures Tailored by Combinatorial Processes in an Al-Cu-Mg-Si Alloy

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Acta Metallurgica Sinica(English Letters) 2020年第11期33卷 1527-1534页

作者： Fengjiao Niu Jianghua Chen cuilan wu Jing wu Xiandong Xu Pan Xie Xiongwei Yu Center for High-Resolution Electron Microscopy College of Materials Science and EngineeringHunan UniversityChangsha 410082China

The 2xxx series Al alloys have been widely used in aerospace industry owing to their high strength,good plasticity and superior *** ensure a good control of shape,the quenched alloy sheets require a small pre-deformation before artificial ***,this pre-deformation considerably deteriorates the mechanical strength of the Al-3.0 Cu-1.8 Mg-0.5 Si(wt%)alloys due to the formation of unfavorable large-sized precipitates at *** tackle this issue,we designed a pre-aging process prior to the *** thermal-mechanical treatment,involving pre-aging,pre-deformation and subsequent aging,markedly enhanced the ultimate tensile strength up to 521 MPa compared to that(448 MPa)of the alloy without *** characterization revealed that the fine precipitates(~2 nm)with a uniform dispersion were promoted within the Al matrix,which in turn partly suppressed the formation of the unfavorable large-sized precipitate(~100 nm).Our findings provide a new clue for designing stronger Al alloys with age-hardenability.

关键词： Aluminum alloys Thermo-mechanical treatment Precipitation Age-hardenability

A Novel Duplex Low-temperature Chromizing Process at 500℃

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Journal of Materials Science & Technology 2007年第6期23卷 823-827页

作者： Huiliang CAO cuilan wu Jiangwen LIU Chengping LUO Ganfeng ZOU School of Mechanical Engineering South China University of Technology Guangzhou 510641 China College of Materials Science and Engineering Hunan University Changsha 410082 China

An optimized low-temperature chromizing process at 500℃ was realized on a plain medium-carbon steel with 0.45 wt pct carbon via a duplex chromizing process which consists of a precursor plasma nitriding, and a followed salt bath thermoreactive deposition and diffusion （TRD） chromizing process. CrN layer with a thin diffusion layer underneath was formed. The duplex chromizing process was studied by optical microscopy （OM）, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. It was found that the chromizing speed at 500℃ was successfully enhanced by adding more Cr-Fe powders into the salt bath, and the CrN layer formed at the cost of the prior nitride compound layer. A CrN layer with average 8.1/~m in thickness and 1382 HV0.01 in microhardness was formed on the substrate by duplex chromizing at 500℃ for 24 h. Further more, the CrN layer consisted of nanocrystalline CrN grains.

关键词： Chromizing Plasma nitriding Thermoreactive deposition and diffusion (TRD) CrN

Relationship Between the Strengthening Effect and the Morphology of Precipitates in Al–7.4Zn–1.7Mg–2.0Cu Alloy

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Acta Metallurgica Sinica(English Letters) 2014年第6期27卷 1070-1077页

作者： Xiubo Yang Jizi Liu Jianghua Chen Caiyun Wan Lei Fang Ping Liu cuilan wu College of Materials Science & Engineering Hunan University Hunan Province Key Laboratory for Spray Deposition Technology and Application Hunan University

The morphological evolution of the precipitates in Al–7.4Zn–1.7Mg–2.0Cu（wt%） alloy was studied by highresolution transmission electron microscopy（HRTEM）. Statistics reveal that the hardness of the alloy changes accordingly with the change of the average thickness–diameter ratio of precipitates. The GPII zones are mainly responsible for the first and also the highest hardness peak. They grow in diameter and keep 7-atomic-layer in thickness. Once the thickness changes, the phase transformation from GPII zone to g0 or g-precursor would occur. The resultant metastable g0 and g-precursor precipitates grow in both diameter and thickness, but much faster in the former. After the first hardness peak,the metastable g0 precipitates and g-precursor, coexisting with part of GPII zones, are counted as the main hardening precipitates.

关键词： Aluminum alloys Precipitates Age hardening Electron microscopy Morphology