检索结果-内蒙古大学图书馆

Thickness-Dependent microstructure in Additively Manufactured Stainless Steel

JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE 2021年第9期30卷 6606-6617页

作者： Vyatskikh, Alexandra L. Slagle, Thomas B. Jiang, Sen El-Azab, Salma A. Bertoli, Umberto Scipioni Valdevit, Lorenzo Lavernia, Enrique J. Schoenung, Julie M. Univ Calif Irvine Dept Mat Sci & Engn 544 Engn Tower Irvine CA 92617 USA

Widespread industrial adoption of metal additive manufacturing (AM) requires an in-depth understanding of microstructural evolution during AM. In this study, the effect of process parameters and feature thickness on the microstructures of 316L stainless steel components fabricated by laser powder bed fusion (LPBF) was examined. A standard benchmark geometry developed by the National Institute of Standards and Technology, which contained walls of 0.5, 2.5 and 5.0 mm in thickness, was used. Optical microscopy, finite element analysis, scanning electron microscopy and electron backscatter diffraction revealed dramatic microstructural differences in features of different thickness within the same component. The feature thickness influenced the cooling rate, which in turn impacted the melt pool size, solidification microstructure, grain morphology and density of geometrically necessary dislocations. The relationship between feature size and grain morphology was dependent on the energy input used during LPBF. Such behavior suggested that local manipulation of LPBF process parameters can be employed to achieve microstructural homogeneity within the as-printed stainless steel components.

关键词： additive manufacturing laser powder bed fusion microstructure development stainless steel

来源：评论

学校读者我要写书评

暂无评论

Fabrication and properties of pressure-sintered reaction-bonded Si₃N₄ ceramics with addition of Eu₂O₃-MgO-Y₂O₃

引用

CERAMICS INTERNATIONAL 2021年第1期47卷 935-942页

作者： Wu, Li-Xiang Zhu, Lin-Lin You, Yang Lin, Rui-Lin Liu, Qing-Qing Guo, Wei-Ming Lin, Hua-Tay Plucknett, Kevin Paul Guangdong Univ Technol Sch Electromech Engn Guangzhou 510006 Peoples R China Guangdong Univ Technol Sch Chem Engn & Light Ind Guangzhou 510006 Peoples R China Dalhousie Univ Dept Mech Engn Halifax NS B3H 4R2 Canada

Dense pressure-sintered reaction-bonded Si3N4 (PSRBSN) ceramics were obtained by a hot-press sintering method. Precursor Si powders were prepared with Eu2O3-MgO-Y2O3 sintering additive. The addition of Eu2O3-MgO-Y2O3 was shown to promote full nitridation of the Si powder. The nitrided Si3N4 particles had an equiaxial morphology, without whisker formation, after the Si powders doped with Eu2O3-MgO-Y2O3 were nitrided at 1400 degrees C for 2 h. After hot pressing, the relative density, Vickers hardness, flexural strength, and fracture toughness of the PSRBSN ceramics, with 5 wt% Eu2O3 doping, were 98.3 +/- 0.2%, 17.8 +/- 0.8 GPa, 697.0 +/- 67.0 MPa, and 7.3 +/- 0.3 MPa m(1/2), respectively. The thermal conductivity was 73.6 +/- 0.2 W m(-1) K-1, significantly higher than the counterpart without Eu2O3 doping, or with ZrO2 doping by conventional methods.

关键词： Pressure-sintered reaction-bonded Si3N4 Hot-pressing microstructure development Mechanical properties Thermal conductivity

来源：评论

学校读者我要写书评

暂无评论

microstructure development of thermoplastic polyurethanes under compression: The influence from first-order structure to aggregation structure and a structural optimization

引用

POLYMER 2012年第5期53卷 1138-1147页

作者： Li, Cong Han, Jingjie Huang, Qishian Xu, Hongxing Tao, Jian Li, Xiuhong Yantai Wanhua Polyurethanes Co Natl Polyurethanes Engn Res Ctr Yantai 264000 Shandong Peoples R China E China Univ Sci & Technol Key Lab Pressure Syst & Safety Minist Educ Shanghai 200237 Peoples R China Shanghai Synchrotron Radiat Facil Shanghai 200100 Peoples R China

The microstructure development of 4,4'-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO) based thermoplastic polyurethane (TPU) under compression was investigated. Influential factors on the permanent compression deformation were discussed in detail. Two types of samples with the same chemical compositions while different aggregation structures were prepared by altering the stirring speed during the synthesis process. The difference in the first-order structure of these samples was studied by C-13 NMR. The aggregation structures and the corresponding development under compression were characterized by DSC, WAXD and SAXS, respectively. These observed results indicated that difference of microstructures lead to different deformation behaviors, and the disruption of hard segment domains or reorganized structures by less ordered hard segments played significant roles in the permanent deformation under compression. The viscoelastic behaviors of these samples were described by DMA and simulated by Rouse model. The derived terminal viscosity and relaxation times were used to explain the different permanent deformations of these samples. Finally, an optimized micro-crosslink structure was introduced in TPUs, and a better deformation resistance property was obtained. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.

关键词： Thermoplastic polyurethanes microstructure development Compression

来源：评论

学校读者我要写书评

暂无评论

microstructure development and fracture toughness of acid-treated carbon nanofibers/alumina composites

引用

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 2012年第1408期120卷 560-568页

作者： Ueda, Naoki Yamakami, Tomohiko Yamaguchi, Tomohiro Kitajima, Kunio Usui, Yuki Aoki, Kaoru Endo, Morinobu Saito, Naoto Taruta, Seiichi Shinshu Univ Fac Engn Nagano 3808553 Japan Shinshu Univ Sch Med Matsumoto Nagano 3908621 Japan Shinshu Univ Sch Hlth Sci Dept Appl Phys Therapy Matsumoto Nagano 3908621 Japan

In this study, carbon nanofibers (CNFs) having different amounts of defect were prepared by acid-treating for 0.5, 1 and 5 h and were combined with alumina. Then, the influence of the amount of defect on the CNFs on microstructure development of the CNFs/alumina composites and relationship between the fracture toughness and the average alumina grain size was investigated. The intensity ratio of D-band to G-band (D/G) in Raman spectra of the CNFs increased from 0.34 for pristine CNFs to 0.95 for the CNFs acid-treated for 5 h with the acid-treatment time, which indicates that the amount of defect on the CNFs increased with the acid-treatment time. The alumina grain growth in the dense composites sintered at 1200-1300 degrees C was not influenced by the amount of defect on the CNFs, however, the composite containing CNFs having the moderate amount of defect (D/G = 0.56) showed the slowest alumina grain growth rate at 1350-1450 degrees C. The fracture toughness of the composites containing the CNFs acid-treated for 0.5 h increased with a decrease in average alumina grain size and reached 5.6 MPa.m(0.5) at the average alumina grain size of 0.84 mu m, which was 60% higher value compared to monolithic alumina (3.5 MPa.m(0.5)). However, fracture toughness of the composites containing CNFs acid-treated for 1 and 5 h increased with a decrease in average alumina grain size, showed the maximum values of 5.0 and 4.5 MPa.m(0.5) at average alumina grain sizes of 1.3 and 1.6 mu m, respectively, and decreased as the average alumina grain size decreased further. The maximum fracture toughness of the composite containing the CNFs acid-treated for 5 h was lower than that of the composite containing the CNFs acid-treated for 1 h. (C)2012 The Ceramic Society of Japan All rights reserved.

关键词： Alumina Carbon nanofibers Composite Fracture toughness microstructure development

来源：评论

学校读者我要写书评

暂无评论

Dynamic recrystallization behavior under steady and transient mutation deformation state

引用

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES microstructure AND PROCESSING 2022年 843卷 1页

作者： Liu, Caiyi Barella, Silvia Peng, Yan Sun, Jianliang Guo, Shuo Liang, Shicheng Gruttadauria, Andrea Mapelli, Carlo Yanshan Univ Natl Engn Res Ctr Equipment & Technol Cold Strip Qinhuangdao 066004 Hebei Peoples R China Politecn Milan Dept Mech Engn I-20156 Milan Italy

Dynamic recrystallization (DRX), which is a critical regulatory procedure in the hot rolling process, can greatly improve the microstructure of metallic materials. In recent years, the development of innovative rolling equipment technology (flexible rolling and ring rolling) has brought new challenges to the traditional DRX steady deformation state regulating procedure. In this paper, the coupled behaviors of DRX hot deformation parameters in the constant and transient mutation deformation state of metallic materials are investigated. By analyzing the flow stress curves, DRX was found to be the predominant softening mechanism. The Zener-Hollomon equation is established under a stable deformation state, coupling stress, strain rate, and deformation temperature. A new DRX model, based on the integration of different algorithms found in the literature, is proposed to predict the DRX volume fraction. These values are in good agreement with the experimental ones. Furthermore, electron backscattering diffraction (EBSD) was used to characterize the microstructural morphology under steady and transient mutation deformation state. The DRX mechanisms were understood for all of the stain rate transient mutations and for the flexible rolling dynamic deformation state as CDRX to DDRX and then to CDRX.

关键词： Dynamic recrystallization Steady deformation Transient mutation deformation Hot deformation microstructure development

来源：评论

学校读者我要写书评

暂无评论

Impact of Exposure on Thin Epoxy Overlay Performance

Impact of Exposure on Thin Epoxy Overlay Performance

引用

作者： Mazumder, Abul Fazal Western Michigan University

学位级别：Ph.D., Doctor of Philosophy

Thin epoxy overlays are used for improving the condition and extending the service life of bridge decks. The tensile bond pull-off strength, evaluated as per the ASTM C1583, is used as the performance indicator. A failure in the substrate with a tensile strength of 250 psi or greater is considered acceptable. However, the performance evaluated on in-service bridge decks shows inconsistent results. Laboratory studies by several researchers documented a distinct performance difference when the overlays are exposed to room temperatures in comparison to elevated temperatures. However, the most influential parameters such as concrete surface profile, thermal compatibility between overlay and concrete, the variation of substrate moisture against temperature, epoxy softening, and mechanical and interface epoxy properties under elevated temperatures were not measured and correlated to the observed performance. The performance of a concrete-overlay system depends on the mechanical and interface properties of epoxy, concrete surface profile, concrete properties, and exposure conditions. This study included experimental and numerical investigations to provide clarifications to the observed performance differences by evaluating the impact of concrete age at the time of epoxy application, concrete mix ingredients, exposure conditions, concrete microstructure development, substrate moisture and temperature, concrete surface profile, and epoxy properties on the performance of two epoxy overlays. Experimental results confirm that (i) the performance of epoxy overlays improves when the concrete mix contains slag and (ii) substrate moisture vapor pressure and epoxy softening under elevated temperature negatively affect the overlay performance. The concrete/epoxy bond interface undergoes higher degradation when subjected to an elevated temperature. The results obtained from the numerical analyses indicate a concrete surface profile of 6–8 with a height-space ratio of surface irregular

关键词： Concrete-overlay system Interface Mechanical properties Concrete age Mix ingredients microstructure development Moisture and temperature Surface profile Epoxy properties Slag

来源：评论

学校读者我要写书评

暂无评论

Introduction of Dendrite Fragmentation in microstructure Calculation by Cellular Automaton Method

引用

ISIJ INTERNATIONAL 2020年第1期60卷 99-105页

作者： Morita, Shugo Miki, Yuji Toishi, Keigo JFE Steel Corp Steel Res Lab Kokan Cho1 Fukuyama Hiroshima 7218510 Japan

Control of the solidification microstructure in continuous casting of steel is necessary because the microstructure affects material properties. In order to predict the solidification microstructure, the effect of dendrite fragmentation was indirectly introduced in the cellular automaton method by using V-crit, which is the velocity threshold of the molten steel flow. Calculations were carried out with various V-crit (200 mu s(-1) <= V-crit <= 1 mms(-1)), and the results were compared with the results of a casting experiment using high carbon steel. The observed specimens were extracted from the upper part and lower part of casting. Equiaxed grains and branched columnar grains were observed in the microstructure of the upper specimen, whereas only columnar grains were observed in the microstructure of the lower specimen. The calculation results with V-crit greater than 400 mu m showed good qualitative agreement with the microstructures of both observed specimens. The microstructures were calculated because the flow velocity of the molten steel around the upper specimen was much greater than that around the lower specimen. There is a possibility that solute transportation, which induces fragmentation, occurs even if the velocity of the molten steel flow is on the order of 10(-4) ms(-1).

关键词： microstructure development numerical simulation fragmentation cellular automaton method center segregation

来源：评论

学校读者我要写书评

暂无评论

Synthesis, densification and characterization of Ag doped ceria nanopowders

引用

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 2020年第5期40卷 1983-1988页

作者： Matovic, Branko Butulija, Svetlana Dohcevic-Mitrovic, Zorana Arsic, Tamara Minovic Lukovic, Jelena Boskovic, Snezana Maletaskic, Jelena Inst Nucl Sci Vinca POB 522 Belgrade 11001 Serbia

Nanosized Ag-doped ceria (Ce1-xAlxO2-delta)powders (0.1 <= x <= 0.04) were obtained by self-propagating room temperature reaction. The solid solubility of Ag into ceria lattice was the highest reported so far. X-ray diffraction analysis and field emission scanning microscopy results showed that the doped samples are single phase solid solutions with fluorite-type structure and all prepared powders were nanometric in size. The average size of Ce(1-x)Ag(x)O2-square particles lies at about 4 nm. Raman spectra revealed an increase in the amount of oxygen vacancies with the increase of Ag concentration, such as is foreseen. The thermal stability of solid solution was followed by XRD. microstructure development was studied by scanning electron microscopy. By controlling the processing variables, it was possible to obtain high density samples with homogeneous microstructure at low sintering temperature.

关键词： Nanopowders Ceria Phase stability microstructure development Densification

来源：评论

学校读者我要写书评

暂无评论

How the Thermomechanical Processing Can Modify the High Strain Rate Mechanical Response of a Microalloyed Steel

引用

MATERIALS 2021年第20期14卷 6062-6062页

作者： Bloniarz, Remigiusz Majta, Janusz Rutkowski, Bogdan Korpala, Grzegorz Prahl, Ulrich Janiszewski, Jacek Lisiecka-Graca, Paulina AGH Univ Sci & Technol Fac Met Engn & Ind Comp Sci PL-30059 Krakow Poland TU Bergakad Freiberg Inst Met Forming D-09599 Freiberg Germany Mil Univ Technol Fac Mechatron Armament & Aerosp PL-00908 Warsaw Poland

The effects of thermomechanical processing (TMP) on the mechanical response of microalloyed steels subjected to dynamic loading conditions were examined. The deformation conditions in the thermomechanical laboratory rolling processes were selected on the basis of dilatometric tests. It allowed (with a constant value of total deformation) us to obtain microstructures with different compositions and morphology of the particular components. Several samples characterized by a particularly complex and unexpected representation of the obtained microstructures were selected for further research. Plastometric tests, i.e., compression and tensile tests, were performed under quasi-static loading with digital image correlation (DIC) analysis, and under dynamic loading on the Split Hopkinson Pressure Bar (SHPB) apparatus with strain rates of 1400 and 2000 s(-1). Samples deformed in such conditions were subjected to microstructural analysis and hardness measurements. It has been observed that the use of various combinations of TMP parameters can result in the formation of specific microstructures, which in turn are the source of an attractive mechanical response under dynamic loading conditions. This opens up new possible areas of application for such popular structural materials which are microalloyed steels.

关键词： thermomechanical processing microalloyed steel dynamic loading mechanical properties microstructure development

来源：评论

学校读者我要写书评

暂无评论

Possibility and advantages of producing an ultra-high performance concrete (UHPC) with ultra-low cement content

引用

CONSTRUCTION AND BUILDING MATERIALS 2021年 273卷 122023-122023页

作者： Ding, Mengxi Yu, Rui Feng, Yuan Wang, Siyu Zhou, Fengjiao Shui, Zhonghe Gao, Xu He, Yongjia Chen, Luyi Wuhan Univ Technol State Key Lab Silicate Mat Architectures Wuhan 430070 Peoples R China State Key Lab Hlth & Safety Bridge Struct Wuhan 430034 Peoples R China Wuhan Univ Technol Int Sch Mat Sci & Engn Wuhan 430070 Peoples R China Wuhan Univ Technol Adv Engn Technol Res Inst Zhongshan City Xiangxing Rd 6 Zhongshan 528400 Guangdong Peoples R China Wuhan Univ Technol Sch Civil Engn & Architecture Wuhan 430070 Peoples R China

This study aims to clarify the possibility and advantages of producing an Ultra-High Performance Concrete (UHPC) with ultra-low cement content. The UHPC matrix is designed on the basis of the improved Andreasen and Andersen particle packing model (A&A), and then up to 73% (wt.) of cement clinker is replaced by inactive fillers. After that, the effects of large quantity of inactive fillers on UHPC fresh and hardened behaviors are investigated. The experimental results indicate that the reduction of binder content is beneficial for improving the UHPC workability and decreasing its cracking risk. However, when the added cement clinker amount is reduced to about 245 kg/m(3) concrete, the compressive strength, durability and pore structure of UHPC deteriorate greatly. Hence, to guarantee the mechanical capacity and sustainable development of UHPC simultaneously, the modified MA model should be used to design a dense meso-skeleton, while the minimum cement clinker amount can be reduced to about 280 kg/m(3) concrete. Additionally, the hydration kinetics and microstructure development of the newly designed UHPC are correspondingly analyzed and discussed. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Ultra-high performance concrete (UHPC) Low binder content Cracking risk Hydration kinetics microstructure development

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：