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Effect of V and V-N Microalloying on Deformation-Induced Ferrite Transformation in Low Carbon Steels

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Journal of Materials Science & Technology 2006年第2期22卷 159-163页

作者： Kai WANG Lijun WANG Wenfang CUI chunming liu School of Materials and Metallurgy Northeastern University Shenyang 110004 China

Deformation-induced ferrite transformation （DIFT） has been proved to be an effective approach to refine ferrite grains. This paper shows that the ferrite grains can further be refined through combination of DIFT and V or V-N microalloying. Vanadium dissolved in γ matrix restrains DIFT. During deformation, vanadium carbonitrides rapidly precipitate due to strain-induced precipitation, which causes decrease in vanadium dissolved in matrix and indirectly accelerates DIFT. Under heavy deformation, deformation induced ferrite （DIF） grains in V microalloyed steel were finer than those in V free steel. The more V added to steel, the finer DIF grains obtained. Moreover, the addition of N to V microalloyed steels can remarkably accelerate precipitation of V, and then promote DIFT. However, DIF grains in V-N microalloyed steel easily coarsen.

关键词： Deformation induced ferrite transformation Strain induced precipitation V microalloyed steel V-N microalloyed steel Thermomechanical simulation

Precipitation of Ti 2 Al phases at lamellar interfaces in a high-Nb-containing TiAl alloy during thermal exposure

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Journal of Materials Science & Technology 2022年第31期126卷 132-140页

作者： Dongxu Li Guoying Zhang Gang Lu Yujie liu Jianjun Wang chunming liu Key Laboratory for Anisotropy and Texture of Materials(MOE) School of Materials Science and EngineeringNortheastern UniversityShenyang 110819China College of Physics Science and Technology Shenyang Normal UniversityShenyang 110034China Research Center for Metallic Wires Northeastern UniversityShenyang 110819China

The thermal stability of microstructures is crucial for determining the performance of alloys in extreme *** the present work,the microstructural evolution and precipitation behavior in a high Nb-containing Ti45Al8Nb alloy during thermal exposure at 950°C were *** was found that excessα2 phases in the as-cast microstructure were unstable and tended to decompose during thermal *** Ti 2 Al phases precipitated at lamellar interfaces and had a[1¯10]_(γ)[11¯20]_(α2)[11¯20]_(Ti2Al),(002)_(γ)(1¯100)_(α2)(1¯100)_(Ti2Al)crystallographic orientation relationship(OR)with the *** faults(SFs)generated inα2 phases during theα2→γphase transformation provided favorable nucleation sites for Ti 2 Al phases.

关键词： TiAl alloy Thermal exposure Phase transformation Precipitation

Mathematic model of solid fraction during rheo-casting by the cooling sloping plate process

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Acta Metallurgica Sinica(English Letters) 2012年第1期25卷 81-88页

作者： Renguo GUAN Zhanyong ZHAO Hongqian HUANG Qiusheng ZHANG chunming liu College of Materials and Metallurgy Northeastern UniversityShenyang 110819China

A mathematic model of the solid fraction during rheo-casting by the cooling sloping plate process was established, and the effects of the process parameters on the solid fraction were analyzed. The calculation results show that the experimental result is approximately agreed with the calculation value. The effect of the casting temperature on the change rate of the solid fraction is not obvious. But the beginning solidification length is greatly influenced by the casting temperature. The beginning solidification length increases with the increment of the casting temperature. The effect of the sloping angle on the solid fraction becomes obvious with the increment of the sloping plate length. The solid fraction increases sharply with the decrease of the initial thickness of the melt. The melt initial thickness between 15 and 20 mm is suggested.

关键词： Sloping plate Rheo-casting Mathematic model Solid fraction Parameter

Process Parameter Optimizing and Studies on Microstructure and Properties of AZ31 Alloy Prepared by Semisolid Rolling Process

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Acta Metallurgica Sinica(English Letters) 2013年第3期26卷 293-298页

作者： Renguo GUAN Zhanyong ZHAO Xiang WANG Chunguang DAI chunming liu School of Materials and Metallurgy Northeastern University

A novel continuous semisolid rolling process for producing AZ31 alloy strip was developed. The process parameters were optimized, and microstructure and properties of AZ31 alloy prepared by the process were studied. The results reveal that primary grains of the strip become coarse, and the grain structure transforms from round shape to dendrite with the increment of casting temperature gradually. Eutectic phase fraction and primary grain size increase with the increment of roll speed. The primary grain size decreases firstly and then increases with the increment of the vibration frequency correspondingly. When the casting temperature is from 650℃to 690℃, the roll speed is 0.069 m·s- 1, and the vibration frequency is about 80 Hz, AZ31 alloy strip with a cross section size of 4 mm×160 mm was prepared by the proposed process. The ultimate tensile strength and elongation are improved 1% and 57 %, respectively.

关键词： Semisolid Sloping plate Rolling AZ31 alloy Microstructure Property

Heat transfer and grain refining mechanism during melt treatment by cooling sloping plate

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Acta Metallurgica Sinica(English Letters) 2012年第4期25卷 320-328页

作者： Renguo GUAN Zhanyong ZHAO Runze CHAO Hongqian HUANG chunming liu College of Materials and Metallurgy Northeastern UniversityShenyang 110819China

Heat transfer of flow melt and grain refining mechanism during melt treatment by the cooling sloping plate were investigated. The results show that the cooling sloping plate can refine not only grains of alloys but also can obviously refine pure metal. Cooling ability of the plate is the key factor that induces grain refining, the plate material and the flow amount can affect cooling rate of the melt and thus affect refining effectiveness. The cooling rate of the melt on the cooling sloping plate is much faster than that of the conventional casting process, which can reach 1000 K/s and belongs to meta-rapid solidification scope. The thickness of the temperature boundary layer is much larger than that of the velocity boundary layer on the sloping plate, but the temperature gradient is small in the temperature boundary layer. Under strong cooling action by the cooling plate, most parts of the melt on the plate surface can form undercooling, which causes continuous eruptive nucleation, this is the main grain refining mechanism, and the heterogeneous nucleation on the plate surface is a helpful supplement for the nucleation.

关键词： Grain refining Nucleation Cooling rate Sloping plate Temper-ature boundary layer

Optimization of Grain Boundary Character Distribution in Fe-18Cr-18Mn-0.63N High-Nitrogen Austenitic Stainless Steel

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Acta Metallurgica Sinica(English Letters) 2013年第5期26卷 497-502页

作者： Feng SHI Xiaowu LI Yutong HU Chuan SU chunming liu Institute of Materials Physics and Chemistry College of Sciences Northeastern University School of Materials and Metallurgy Northeastern University

Grain boundary engineering（GBE） is a practice of improving resistance to grain boundary failure of the material through increasing the proportion of low Σ coincidence site lattice（CSL） grain boundaries（special grain boundaries） in the grain boundary character distribution（GBCD）. The GBCD in a cold rolled and annealed Fe-18Cr-18Mn-0.63N high-nitrogen austenitic stainless steel was analyzed by electron back scatter difraction（EBSD）. The results show that the optimization process of GBE in the conventional austenitic stainless steel cannot be well applied to this high-nitrogen austenitic stainless steel. The percentage of low ΣCSL grain boundaries could increase from 47.3% for the solid solution treated high-nitrogen austenitic stainless steel specimen to 82.0% for the specimen after 5% cold rolling reduction and then annealing at 1423 K for 10 *** special boundaries of high proportion efectively interrupt the connectivity of conventional high angle grain boundary network and thus achieve the GBCD optimization for the high-nitrogen austenitic stainless steel.

关键词： High nitrogen austenitic stainless steel Grain boundary character distri-bution CSL grain boundary EBSD

Enhancing the bake-hardening responses of a pre-aged Al-Mg-Si alloy by trace Sn additions

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Journal of Materials Science & Technology 2020年第5期40卷 107-112页

作者： Gang Lu Shuai Nie Jianjun Wang Ying Zhang Tianhai Wu Yujie liu chunming liu Key Laboratory for Anisotropy and Texture of Materials(MoE) School of Materials Science and EngineeringNortheastern UniversityShenyang 110819China The State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819China Research Center for Metallic Wires Northeastern UniversityShenyang 110819China Shenyang Industrial Transformation Upgrading Promotion Center Shenyang 110083China

Effects of additions of trace Sn on the bake-hardening responses of a pre-aged Al-0.85 Mg-0.85 Si(in wt%)alloy were investigated through mechanical tests,differential scanning calorimetry,electrical resistivity and transmission electron *** indicate that trace Sn additions reduced the number density of pre-aging clusters by inhibiting the formation of unstable counterpart during pre-aging treatment,leading to low strength and high supersaturation of solute *** a subsequent paint-bake treatment,the presence of highly supersaturated solute atoms and high concentrated free vacancies moderated the activation energy barrier ofβ’’phase and thus kinetically accelerated the formation ofβ’’.Consequently,the trace Sn additions enhanced the bake-hardening responses of the pre-aged alloys *** Sn-containing pre-aged Al-Mg-Si alloys with low strength and great bake-hardening responses hold promising potential for automotive body skin applications.

关键词： Al-Mg-Si alloy Pre-aging Trace Sn Bake-hardening responses Precipitation kinetics

Low complexity Chase-2 decoding of concatenated codes

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Chinese Science Bulletin 2010年第26期55卷 3066-3070页

作者： liu XiaoJian ZHAO chunming SUN XiaoJun National Mobile Communications Research Laboratory Southeast University Nanjing 210096 China

The concatenated codes are widely used in current communication systems, such as satellite communication systems and WiMAX system. The objective of this study was to present a low complexity iterative soft decoding algorithm for concatenated codes. The concatenation was between a Reed-Solomon (RS) code and recursive systematic convolutional (RSC) code. The reduction in computational complexity was achieved by simplifying the Chase-2 decoder for RS codes with limited usage of test patterns. The processing of soft information between inner and outer decoders was also discussed. Simulation results showed that the proposed algorithm could achieve a good trade-off between complexity and performance.

关键词：级联码大通卫星通信系统计算复杂性译码解码算法低复杂度限制使用

Hierarchical strain band formation and mechanical behavior of a heterostructured dual-phase material

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Journal of Materials Science & Technology 2023年第31期162卷 25-37页

作者： Zhongkai Li Yujie liu Yanfei Wang Jun Hu Lei Xu Jianjun Wang chunming liu Yuntian Zhu Key Laboratory for Anisotropy and Texture of Materials of Ministry of Education Northeastern UniversityShenyang 110819China Department of Mechanics and Engineering Science College of EngineeringPeking UniversityBeijing 100871China The State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819China Shi-Changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Department of Materials Science and Engineering City University of Hong KongHong KongChina

Dispersive strain bands have been reported as a characteristic deformation feature of heterostructured materials,which helps to improve ***,their formation mechanism is still not well *** we report the formation of dispersed strain bands through dual-level hierarchical strain banding and its effect on the mechanical behavior of a heterostructured Fe-40Cu model ***,deformation started by the formation and propagation of dispersed microscale strain bands in the heterostructured Fe-40Cu *** strain gradient was generated within the microscale strain bands during their propagation and was accommodated by the accumulation of geometrically necessary disloca-tions(GNDs).The dispersed microscale strain bands were not uniformly distributed,but instead grouped together to form macroscale strain bands that were uniformly distributed over the entire gage section to accommodate the majority of the applied *** formation of this dual-level hierarchical strain bands prevented the formation of large strain localization to fail the sample *** was also found that increasing the strain hardening capacity of soft copper zones provides more room for the accumulation of GNDs,resulting in higher constraint to microscale strain band propagation and consequently higher *** observations suggest the possibility of tailoring microscale strain bands to optimize tensile performance of heterostructured materials.

关键词： Heterostructured materials Strain bands Strain gradient Hetero-deformation induced hardening