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Microstructure-Property Correlation and Strain Partitioning Behavior in Medium-Carbon Carbide-Free Bainitic Steel

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SSRN 2023年

作者： Su, Ru Zheng, Xiongwei Kang, Jie Wu, Dayong Zhang, Fucheng Yang, Zhinan Ma, H.K. Hebei Key Laboratory of Material Near-net Forming Technology School of Materials Science and Engineering Hebei University of Science and Technology Hebei Shijiazhuang050000 China College of Metallurgy and Energy North China University of Science and Technology Tangshan063210 China National Engineering Research Center for Equipment and Technology of Cold Strip Rolling Yanshan University Qinhuangdao066004 China State Key Laboratory of Metastable Materials Science and Technology Yanshan University Qinhuangdao066004 China

This paper investigates the correlation between the microstructure, properties, and strain partitioning behavior in a medium-carbon carbide-free bainitic steel through a combination of experiments and Representative Volume Element (RVE) simulations. The results reveal that as the austempering temperatures increase from low to intermediate, the optimal balance of properties shifts from strength-toughness to plasticity-toughness. The formation of fine bainitic ferrite (BF) plates and bainite sheaves under low austempering temperature enhances both strength and toughness. Conversely, the wide size and shape distribution of the retained austenite (RA) obtained through intermediate austempering temperature contribute to increased work-hardening capacity, resulting in enhanced plasticity. During the tensile deformation simulation, the main bearing phase of stress is BF. Plastic strain is predominantly generated at the interface of the two phases in the blocky RA and within the phase in the narrow channel of the film-like RA. It is predicted that crack initiation points mostly occur at the strain concentration between BF and RA at the two-phase interface, potentially leading to crack propagation along the strain failure zone. Furthermore, the morphology of RA plays a vital role in determining the strain partitioning behavior while the volume fraction of the ductile RA plays a crucial role in enhancing impact toughness. © 2023, The Authors. All rights reserved.

关键词： Carbides

Microstructure, Property and Strain Partitioning Dependence of Medium-Carbon Carbide-Free Bainitic Steel

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SSRN 2023年

作者： Su, Ru Zheng, X.W. Kang, Jie Wu, Dayong Ma, Haikun Zhang, F.C. Yang, Zhinan Hebei Key Laboratory of Material Near-net Forming Technology School of Materials Science and Engineering Hebei University of Science and Technology Hebei Shijiazhuang050000 China College of Metallurgy and Energy North China University of Science and Technology Tangshan063210 China National Engineering Research Center for Equipment and Technology of Cold Strip Rolling Yanshan University Qinhuangdao066004 China State Key Laboratory of Metastable Materials Science and Technology Yanshan University Qinhuangdao066004 China

关键词： Carbides

Density Functional Theory Simulation of PVDF Transition in Electric Field Polarization

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Density Functional Theory Simulation of PVDF Transition in E...

International Conference on Mathematics, Modeling and Simulation Technologies and Applications

作者： Yan Li Xu Ma Yanhong Ding Xudong Li Zisheng Li School of Material Science and Engineering Tianjin University of Technology Tianjin Engineering Center of Near-Net-Shape Forming Technology for Metallic Materials School of Electrical and Electrical and Electronic Engineering Tianjin Key Laboratory of Film Electronic and Communication DevicesTianjin University of Technology

ISBN: (纸本)9781713800361

The molecular model of PVDF is established by the calculation method of density functional theory(DFT).A process of applying an electric field of different magnitude to PVDF to cause a phase transition was *** transformation of the molecular chain of PVDF molecules under the electric field strength below 0.05 Ha was studied in *** is found that the main role in the transformation process is the transformation of the carbon *** we calculated the dipole moment and average molecular polarizability of the PVDF molecular chain under different *** results showed the dipole moment increases from 7.6 Debye to 9.9 Debye with the structure of α PVDF to β PVDF,the mean polarizability also increased from 39.5 to *** calculations provide theoretical calculations for the study of PVDF and demonstrate the effect of electric field polarization on the production of β PVDF.

关键词： DFT PVDF Polarization polyvinylidene fluoride Polarization discrete Fourier transform dipole moments Electric fields computational methods molecular model

Pulsing-Induced Healing of a Surface Crack of a Nickel-Based Alloy

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SSRN 2024年

作者： Wang, Qian Quan, Mingming Tan, Zhen Liu, Ming Wang, Dianlong Yang, Xiao Liu, Ying Mao, Yaning Liang, Zhimin Yang, Fuqian Wang, Liwei School of Material Science and Engineering Hebei University of Science and Technology Shijiazhuang050018 China Hebei Key Laboratory of Material Near-Net Forming Technology Shijiazhuang050018 China School of Mechanical Engineering and Automation Fuzhou University Fuzhou350108 China HBIS Group Materials Institute HBIS Group Hebei Shijiazhuang050023 China Materials Program Department of Chemical and Materials Engineering University of Kentucky LexingtonKY40506 United States School of Material Science and Engineering Australia

In this work, we demonstrate the feasibility of applying electric pulses to heal surface cracks on Ni-based GH4169 alloy under compressive load. There exists an incubation time for the onset of the healing of a crack, which is associated with local temperature at the crack tip. The crack size decreases with increasing the pulsing time at a constant healing rate prior to complete healing of the crack. Increasing compressive load accelerates the healing process. The electric pulsing leads to the formation of an influential zone surrounding the crack with the finest grain sizes in the healed crack and the coarsest grain sizes away from the influential zone. The indentation hardness increases with the increase the distance to the crack tip of the healed crack. A model of viscous flow in the crack channel is proposed for the crack healing. The resultant force on the crack faces due to the crack healing increases with the increase of the healing time and the decrease of the crack width. © 2024, The Authors. All rights reserved.

关键词： Crack tips

Research on the Strengthening Mechanism of Nb-Ti Microalloyed Ultra Low Carbon If Steel

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SSRN 2024年

作者： Zheng, Yaxu Wang, Kun Yang, Qin Lin, Yu Zhu, Liguang Wu, Xiaoyan Han, Baochen Wang, Bo Zhang, Di Feng, Jie Cao, Ruifang School of Material Science and Engineering Hebei Short Process Steel Making Technology Innovation Center Hebei Key Laboratory of Material Near-Net Forming Technology Hebei University of Science and Technology Shijiazhuang050018 China QuesTek Innovations EvanstonIL United States College of Materials Science and Engineering Chongqing University Chongqing400045 China Rolling Operation Department Beijing Shougang Co. LTD. Tangshan064404 China

The microstructure evolution and carbides precipitation behavior during the hot rolling, cold rolling and annealing processes have been studied. The results indicates that the addition of Nb into Ti bearing IF steel promotes the recrystallization at 900 ℃ and obtains fine recrystallized grains. Based on the fine and uniform original structure, Nb-Ti microalloyed steel obtains fine structure after cold rolling and annealing. The study results of the carbides precipitation behavior suggests that the TiN precipitates at high temperature above 1100 ℃, and a large amount of (Nb,Ti)C and TiC precipitate at about 900 ℃ in Nb-Ti and Ti bearing steels, respectively. There is no significantly difference between the amount of carbides in hot deformed steels at 900 ℃ and the hot rolled plates, which indicates that the carbides mainly precipitate during the hot rolling process due to the ultra low carbon and nitrogen content in the steel. However, there is few carbides precipitate during the coiling process at 600 ℃. The thermodynamic and kinetic calculation results are consistent with the TEM observation results. In Nb-Ti containing steel, the solid solution of Nb and Ti elements are significantly reduced due to the large amount precipitation of (Nb,Ti)C during the final rolling process, which effectively promotes the recrystallization of austenite. Therefore, the grains of hot-rolled, cold-rolled, and annealed strips are refined, and the fine-grained strengthening effect is improved. Finally, the strength of Nb-Ti containing steel is higher than that of Ti containing steel. © 2024, The Authors. All rights reserved.

关键词： Microalloying

Enhancing Thermal Stability of Laser-Powder Bed Fusion Fabricated High Entropy Alloy by Introducing Elemental Segregation Using in-situ Alloying

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SSRN 2024年

作者： Zhu, Xiangjian Niu, Mengchao Liu, Shan Yu, Yanan Han, Luyi Zhao, Guoqun Wang, Guangchun State Key Laboratory of Advanced Equipment and Technology for Metal Forming Shandong University Shandong Jinan250061 China Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials Ministry of Education Shandong University Shandong Jinan250061 China Department of Mechanical Engineering Research Institute for Advanced Manufacturing The Hong Kong Polytechnic University Hong Kong The Hong Kong Polytechnic University Shenzhen Research Institute Shenzhen518057 China Hebei Key Laboratory of Material Near-net Forming Technology Hebei University of Science and Technology Hebei Shijiazhuang050000 China

A method is proposed to enhance the thermal stability of laser-powder bed fusion fabricated (L-PBFed) alloys by incorporating Al element segregation through in-situ alloying. The high entropy alloy (HEA) with Al segregation was prepared through in-situ alloying of mixed powders of AlSi10Mg and FeCoCrNi, and the enhanced thermal stability of the grain boundary (GB) and dislocation in high-temperature annealing at 1000 °C and 1200 °C is verified and studied. Experimental characterization and molecular dynamics (MD) simulations revealed that the introduced Al segregation exists in two forms of B2/BCC phases, one in banded shape in the FCC matrix and the other as particles at GBs. At elevated temperatures, short-range uphill diffusion occurs within the banded B2/BCC phase, resulting in the formation of dispersed or mesh-like B2/BCC phases of higher Al and Ni content, along with the generation of dislocations. Additionally, long-range diffusion of Al atoms, originating from the aggregated region of banded B2/BCC, travels to the matrix, utilizing GBs as rapid channels. This diffusion stabilizes GBs by reducing their cohesive energy and maintaining the nailing effect of the B2/BCC phase at GBs. Consequently, the mechanical property exhibits remarkable resistance to softening compared to the traditional L-PBFed alloys. This study demonstrates that element segregation introduced by in-situ alloying serves as an effective approach to enhance the thermal stability of L-PBFed alloys. Furthermore, the proposed theory of sustained phase transitions offers insights into understanding the transitions of heterogeneous alloys fabricated through in-situ alloying at elevated temperatures. © 2024, The Authors. All rights reserved.

关键词： Molecular dynamics

Microstructure and Properties of Copper/Graphene Composites Prepared Via Powder Hot Extrusion

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SSRN 2024年

作者： Chen, Kaili Dong, Jialiang Qiu, Cheng Luo, Zongqiang Zhang, Datong Guangdong Key Laboratory for Advanced Metallic Materials Processing and Forming National Engineering Research Center of Near-net-shape Forming for Metallic Materials South China University of Technology Guangzhou510640 China College of Material Science and Engineering Guizhou Minzu University Guizhou550025 China

Cu/Gr composites have been reported to have high mechanical properties and electrical conductivity, but some of the preparation methods are difficult to execute for industrial production. In this study, Cu/Gr composites were successfully prepared by direct hot extrusion without sintering, and then microstructure, mechanical properties, and electrical conductivity were investigated. Graphene and copper powder were mixed using ultrasonic vibration combined with a V-type mixer. The addition of graphene enhances the mechanical properties of the material, making it have a high electrical conductivity of 94%IACS, and the yield strength and tensile strength are 208 MPa and 233 MPa, respectively. © 2024, The Authors. All rights reserved.

关键词： Graphene

Microstructural Evolution and Hot-Compressive Behavior of Waspaloy Forged Bolts: Experimental and Finite Element Simulation

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SSRN 2023年

作者： Su, Ru Li, Jixiao Wu, Dayong Hu, Fuhong Liang, Xueze Shen, Qingyuan Tian, Wenguang Wang, Yalong Ma, Haikun Narayanaswamy, Balaji Dong, Huicong Wang, Qian Hebei Key Laboratory of Material Near-Net Forming Technology School of Materials Science and Engineering Hebei University of Science and Technology Shijiazhuang050018 China Oriental Bluesky Titanium Technology Co. Ltd Yantai264670 China China Astronautics Standards Institute Beijing100071 China School of Engineering Deakin University Geelong Australia State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing100083 China

This study aims to present the optimum technological parameters of hot forging process of aerospace bolt. Deformation Temperature and strain rate were determined according to relevant conditions for commercial bolt production. Deformation behavior and evolution of microstructure of Waspaloy were investigated using hot isothermal compression tests. The results show that the flow stresses show sufficient sensitivity to the deformation parameters and decreased with increase in deformation temperatures and decrease in strain rates. At high strain rates of 5-10 s-1. Flow curves exhibit a pronounced flow softening. At low strain rates of 0.01-0.1 s-1, the curves demonstrate a dynamic equilibrium. Constitute models of Waspaloy is established and the hot deformation energy is calculated as 446.824 kJ/mol. Microstructures showed that at low temperature (1000-1040°C), grain refinement of DRX is the main mechanism of microstructural evolution, while grain growth kinetics is the dominant mechanism at high temperature (1080-1120°C). DRX kinetics model of this superalloy is established. Also, constitutive and dynamic recrystallization models are brought into the Deform-3D software for validation. The results reveal that the simulation results match well with the experimental results. The study can provide guidance on optimizing technological parameters and predict the microstructure for commercial bolt forging. © 2023, The Authors. All rights reserved.

关键词： Finite element method

Study on Hot Deformation Behavior of Cold-Drawn State Waspaloy and Optimization of Upsetting Process for Bolts

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SSRN 2022年

作者： Su, Ru Li, Jixiao Wang, Qian Hu, Fuhong Liang, Xueze Shen, Qingyuan Tian, Wenguang Wang, Yalong Ma, Haikun Narayanaswamy, Balaji Wu, Dayong Hebei Key Laboratory of Material Near-Net Forming Technology School of Materials Science and Engineering Hebei University of Science and Technology Shijiazhuang050018 China Oriental Bluesky Titanium Technology Co. LTD Yantai264670 China China Astronautics Standards Institute Beijing100071 China School of Engineering Deakin University Geelong Australia State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing100083 China

Mechanical performance of hot forging aviation bolt is strongly related to microstructures and deformation behaviors during hot processing. In order to determine the optimal technological parameters of Waspaloy alloy hot heading bolt, deformation behavior and microstructural evolution of Waspaloy were systematically studied. The experimental design (hot compression) is based on the actual production process parameters. The results from the strain-stress curves showed that there was an obvious flow softening with the decrease of temperature or the increase of strain rate, which can be attribute to the DRX mechanism. A dramatic yield drop was found with the temperature ranging from 1000°C to 1120°C at 1 s-1 due to the short-range ordering of phase forming elements (Ti and Al). Microstructures showed that high temperature and low strain rate promoted DRX behavior, but led to rapid grain growth, which was not conducive to the formation of uniform and fine DRX grains. DRX kinetics model of this superalloy was established based on the experimental results. Furthermore, the developed models were applied in the finite element simulation method (FEM). Combined with microstructure observation, "dead zone" of the bolt was prone to abnormal grain growth, resulting in mixed crystals and reducing the service life of the bolt. The calculated results in terms of grain sizes conform well to experimental ones, which implies a good application prospect of the theoretical calculation. With the two models, an optimization technology was put forward which could predict the microstructures in the aim of high fraction of DRX and fine DRX grains for Waspaloy during the bolt heading process. This study can provide guidance on commercial bolt heading process. © 2022, The Authors. All rights reserved.

关键词： Finite element method