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Oxide dispersion strengthened stainless steel 316L with superior strength and ductility by selective laser melting

Journal of Materials Science & Technology 2020年第7期42卷 97-105页

作者： Yuan Zhong Leifeng Liu Ji Zou Xiaodong Li Daqing Cui zhijian shen Department of Materials and Environmental Chemistry Arrhenius LaboratoryStockholm UniversitySE-10691 StockholmSweden School of Metallurgy and Materials University of BirminghamB152TT UK Department of Chemistry-Radiochemistry P.O.Box 55FI-00014 University of HelsinkiFinland

Dense oxide dispersion strengthened(ODS) 316 L steels with different amount of Y2O3 additions were succe s s fully fabricated by selective laser melting(SLM) even though part of the added Y2O3 got lost during the process.The microstructure was characterized in details and the mechanical properties were tested at room temperature,250℃ and 400℃,respectively.The effect of the scanning speed on agglomeration of nanoparticles during SLM process was discussed.Superior properties,e.g.,yield strength of 574 MPa and elongation of 91%,were achieved at room temperature in SLM ODS 316 L with additional 1% of Y2 O3.At elevated temperature s,the strength kept high but the elongations dropped dra matically.It was observed that nano-voids nucleated throughout the whole gauge section at the sites where nanoinclusions located.The growth and coalescence of these voids were suppre s sed by the formation of an element segregation network before necking,which relieved local stress concentration and thus delayed necking.This unusual necking behavior was studied and compared to the previous theory.It appeared that the strong convection presented in the melt pool can evenly redistribute the short-time milled coarse Y2O3 precursor powder during SLM process.These findings can not only solve the problems encountered during the fabrication of ODS components but also replenish the strengthening mechanism of SLM 316 L thus pave a way for further improving of mechanical properties.

关键词： ODS steel Selective laser melting(SLM) Elevated-temperature properties Necking Strain hardening

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Laser melted oxide ceramics:Multiscale structural evolution with non-equilibrium features

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Journal of Materiomics 2019年第3期5卷 436-445页

作者： Lu Song Jing Ma Qinghua Zhang zhijian shen State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing100084China Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing100190China Department of Materials and Environmental Chemistry Arrhenius LaboratoryStockholm UniversityStockholm10691Sweden

Compared with the versatility in metal industry,application of laser on oxide ceramics is quite limited due to the intrinsic features of ceramics and limited understanding in laser-ceramic interaction mechanism,especially for high-energy laser that causes melting of materials.In this research,a study into general behaviors of several oxide ceramics melted by laser under inert atmosphere is presented.Key factors in determining state transformation,chemical reduction and phase structure are summarized,with further investigation into the evolution in microstructure at multiscale and the corresponding novelty and metastability.It is found that laser melting does show great potential in introducing deep reduction,unique microstructure,and notable increase in structure complexity and total entropy,and those features could contribute to some unconventional functional performance with brand-new structure-property relationship.

关键词： Laser Oxide ceramic Heterogeneity Defects Non-equilibrium

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Specific heat treatment of selective laser melted Ti-6AI-4V for biomedical applications

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Frontiers of Materials Science 2015年第4期9卷 373-381页

作者： Qianli HUANG Xujie LIU Xing YANG Ranran ZHANG zhijian shen Qingling FENG Key Laboratory of Advanced Materials of Ministry of Education of China School of Materials Science and Engineering Tsinghua University Beijing 100084 China

The ductility of as-fabricated Ti-6AI-4V fails far short of the requirements for biomedical titanium alloy implants and the heat treatment remains the only applicable option for improvement of their mechanical properties. In the present study, the decomposition of as-fabricated martensite was investigated to provide a general understanding on the kinetics of its phase transformation. The decomposition of as- fabricated martensite was found to be slower than that of water-quenched martensite. It indicates that specific heat treatment strategy is needed to be explored for as.fabricated Ti-6AI-4V. Three strategies of heat treatment were proposed based on different phase transformation mechanisms and classified as subtransus treatment, supersolvus treatment and mixed treatment. These specific heat treatments were conducted on selective laser melted samples to investigate the evolutions of microstructure and mechanical properties. The subtransus treatment leaded to a basket-weave structure without changing the morphology of columnar prior β grains. The supersolvus treatment resulted in a lamellar structure and equiaxed β grains. The mixed treatment yielded a microstructure that combines both features of the subtransus treatment and supersolvus treatment. The subtransus treatment is found to be the best choice among these three strategies for as.fabricated Ti-6AI-4V to be used as biomedical implants.

关键词： titanium alloy selective laser melting （SLM） heat treatment microstruc-ture mechanical property

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Effect of Build Direction on Fatigue Performance of L-PBF 316L Stainless Steel

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Acta Metallurgica Sinica(English Letters) 2020年第4期33卷 539-550页

作者： Chenfan Yu Yuan Zhong Peng Zhang Zhenjun Zhang Congcong Zhao Zhefeng Zhang zhijian shen Wei Liu State Key Laboratory of New Ceramic and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China Department of Materials and Environmental Chemistry Arrhenius LaboratoryStockholm University10691 StockholmSweden Laboratory of Fatigue and Fracture for Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China

The microstructure and fatigue and tensile properties of 316 L stainless steel fabricated via laser powder bed fusion(L-PBF)were investigated.Two 316 L stainless steel specimens with different loading directions which are either perpendicular to or parallel to building direction were prepared by L-PBF process.The results of X-ray diffraction tomography showed that there was no significant difference in morphology and size/distribution of the defects in the HB and VB samples.Since long axis of columnar grains is generally parallel to the build direction,the fatigue crack encounters more grain boundaries in VB samples under cyclic loading,which led to enhanced fatigue resistance of VB samples compared with HB sample.In contrast to HB sample,the VB sample has a higher fatigue strength due to a higher resistance to localized plastic deformation under cyclic loading.The differences in fatigue properties of L-PBF 316 L SS with different build directions were predominantly controlled by solidification microstructures.

关键词： Austenitic stainless steel Laser powder bed fusion Tensile properties Fatigue strength

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A general mechanism of grain growth-Ⅱ: Experimental

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Journal of Materiomics 2021年第5期7卷 1014-1021页

作者： Jianfeng Hu Junzhan Zhang Xianhao Wang Jun Luo Zhijun Zhang zhijian shen School of Materials Science and Engineering Shanghai UniversityShanghai 200444China College of Materials and Mineral Resources Xi’an University of Architecture and Technology13 Yanta RoadXi’an 710055China Department of Materials and Environmental Chemistry Arrhenius LaboratoryStockholm UniversityS-10691 StockholmSweden Carl Zeiss Co. Shanghai60 Meiyue RoadShanghai 200131China Materials Genome Institute Shanghai UniversityShanghai 200444China

The formed microstructure inside polycrystalline materials strongly influences their practical performances,which process is mostly dominated by grain growth behaviors.However,the general evolution of grain growth behaviors,especial for the occurrence of abnormal grain growth and stagnant growth,remains ambiguous despite decades of efforts.Here,we investigate systematically the general evolution of grain growth behaviors by combining a new grain growth theory with grain growth experiments in SrTiO_(3) polycrystalline materials.The results demonstrate that the observed evolution of grain growth behaviors is in accord with the theoretical predictions,which reveals that the abnormal and stagnant behaviors of grain growth may intrinsically occur in polycrystalline systems due to the existence of nonzero step free energy for grain growth.Furthermore,the general growth theory reveals that normal grain growth results from the roughening transition of grain boundaries which corresponding to step free energy equal to zero.Besides the lower GB energy as commonly believed,the narrower grain size distribution is revealed to play an important role on the thermal stability of grains,which may lead to the counter-intuitive phenomenon of smaller nano-sized grains with higher thermal stability as recently reported in the literature.The general,quantitative growth theory may offer an accurate guidance for the microstructural design with optimal physical properties in polycrystalline materials.

关键词： Grain growth Abnormal grain growth Growth kinetics Grain size distribution Sintering

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A general mechanism of grain growth-Ⅰ.Theory

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Journal of Materiomics 2021年第5期7卷 1007-1013页

作者： Jianfeng Hu Xianhao Wang Junzhan Zhang Jun Luo Zhijun Zhang zhijian shen School of Materials Science and Engineering Shanghai UniversityShanghai200444China Carl Zeiss Co. Shanghai60 Meiyue RoadShanghai200131China College of Materials and Mineral Resources Xi’an University of Architecture and Technology13 Yanta RoadXi’an710055China Department of Materials and Environmental Chemistry Arrhenius LaboratoryStockholm UniversityS-10691StockholmSweden Materials Genome Institute Shanghai UniversityShanghai200444China

The behaviors of grain growth dominate the formation of the microstructure inside polycrystalline materials and thus strongly influence their practical performances.However,grain growth behaviors still remain ambiguous and thus lack a mathematical formula to describe the general evolution despite decades of efforts.Here,we propose a new migration model of grain boundary(GB)and further derive a mathematical expression to depict the general evolution of grain growth in the cellular structures.The expression incorporates the variables influencing growth rate(e.g.GB features,grain size and local grain size distribution)and thus reveals how the normal,abnormal and stagnant behaviors of grain growth occur in polycrystalline systems.In addition,our model correlates quantitatively GB roughening transition with grain growth behavior.The general growth theory may provide new insights into the GB thermodynamics and kinetics during the cellular structure evolution.

关键词： Grain boundary migration Grain growth Roughening transition Abnormal grain growth

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Ordered coalescence of nano-crystals in alkaline niobate ceramics with high remanent polarization

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Journal of Materiomics 2017年第4期3卷 267-272页

作者： zhijian shen Daniel Gruner Mirva Eriksson Lyubov M.Belova Ce-Wen Nan Haixue Yan Department of Materials and Environmental Chemistry Arrhenius LaboratoryStockholm University10691StockholmSweden Department of Materials Science and Engineering Royal Institute of Technology10044StockholmSweden School of Materials Science and Engineering Tsinghua UniversityBeijing100084China School of Engineering and Materials Science Queen Mary University of LondonMile End RoadLondonE14NSUK

Lead-free alkali niobates Na_(0.5)K_(0.5)NbO_(3)(NKN)ceramics,with significantly enhanced ferroelectric remanent polarization(Pr),were prepared using Spark Plasma Sintering(SPS).Three types of boundaries were observed in the ceramics,being grain boundaries between faceted grains,domain boundaries that separate ferroelectric domains inside individual grains,and nanoscale sub-grain boundaries that reveal the nano-scale mosaicity of individual grains.Part of the sub-grain boundaries were from initial powder particles.The other sub-grain boundaries were built by ordered coalescence of nano-crystals during rapid SPS process.It was worthwhile to emphasize that the ordered coalescence of nano-crystals in bulk ceramics during sintering takes place and completes within minutes.These sub-grain features would disappear at higher temperature by long time sintering.Rapid Spark Plasma Sintering allowed us to capture this transient microstructure.The significantly enhanced ferroelectric Pr of NKN was attributed to nanoscale sub-boundaries,which stimulated the dynamics of ferroelectric domain formation and switching.

关键词： Lead-free NKN SPS Remanent polarization Ordered coalescence

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Self-supported yttria-stabilized zirconia mesocrystals with tunable mesopores prepared by a chemi-thermal process

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Journal of Materiomics 2019年第3期5卷 350-356页

作者： Leifeng Liu Mirva Eriksson Ji Zou Yuan Zhong Qi Liu Zhi Liu Yu-Lung Chiu zhijian shen Department of Materials and Environmental Chemistry Arrhenius LaboratoryStockholm University10691StockholmSweden School of Metallurgy and Materials University of BirminghamB152TTUK Department of Materials Science and Engineering South University of Science and Technology of China518055China Size Materials Co. JiujiangChina

Mesoporous mesocrystals are highly desired in catalysis,energy storage,medical and many other applications,but most of synthesis strategies involve the usage of costly chemicals and complicated synthesis routes,which impede the commercialization of such materials.During the sintering of dense ceramics,coarsening is an undesirable phenomenon which causes the growth of the grains as well as the pores hence hinders the densification,however,coarsening is desired in the sintering of porous ceramics to expand the pore sizes while retaining the total pore volume.Here we report a chemi-thermal process,during which nanocrystallite aggregates were synthesized by hydrothermal process and then converted to the product by sintering.Through this strategy,we synthesized mesoporous self-supported mesocrystals of yttria-stabilized zirconia with tunable pore size and the process was then scaled-up to industrial production.The thermal conductivity measurement shows that the mesoporous powder is a good thermal isolator.The monolith pellets can be obtained by SPS sintering under high pressure and the mesoporosity is retained in the monolith pellets.This work features facile and scalable process as well as low cost raw chemicals making it highly desirable in industrial applications.

关键词： Mesocrystal Mesoporous Yttria-stabilized zirconia Industry production

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Recent progress of cobalt-based electrocatalysts for water splitting: Electron modulation, surface reconstitution, and applications

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Nano Research 2024年第4期17卷 2234-2269页

作者： zhijian Liang Di shen Lei Wang Honggang Fu Key Laboratory of Functional Inorganic Material Chemistry Ministry of Education of the People’s Republic of ChinaHeilongjiang UniversityHarbin 150080China

Electrocatalytic water splitting is an essential and effective means to produce green hydrogen energy structures,so it is necessary to develop non-precious metal catalysts to replace precious metals.Cobalt-based catalysts present effective alternatives due to the diverse valence states,adjustable electronic structures,and plentiful components.In this review,the catalytic mechanisms of hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)for electrocatalytic water splitting are described.Then,the synthesis strategies of various cobalt-based catalysts are systematically summarized,followed by the relationships between the structure and performance clarified.Subsequently,the effects of d-band center and spin regulation for cobalt-based catalysts are also discussed.Furthermore,the dynamic electronic and structural devolution of cobalt-based catalysts are elucidated by combining a series of in-situ characterizations.Finally,we highlight the challenges and future developed directions of cobalt-based catalysts for electrocatalytic water splitting.

关键词： cobalt-based electrocatalysts water splitting electron modulation surface reconfiguration

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Comparative study on traumatic effect and L-selectin change made by two blooddrawing modes in rat

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Journal of Nanjing Medical University 2005年第4期19卷 206-209页

作者： Jingye Pan Dakai Chen zhijian shen Lei Chen Weixing Zhu ICU the First Affilliated Hospital of Wenzhou Medical Collage Wenzhou 325000 China

Objective： To compare carotid catheters blooddrawing and tail-cut blooddrawing in traumatizing rats and changing their intemal L-selectin. Methods： Two ways of bloodletting were selected to produce hemorrhagic shock models. Monoclonal antibody sign and flow cytometer were used to test neutrophil L-selectin dynamic expression in rats. Results： No remarkable differences were shown among different time points in neutrophil L-selectin expressing amount （ average fluorescence index）（ P 〉 0.05）. Compared with the normal control group, all cell surface expressions in empirical control group increased. Cell surface expressions reached the summit at 3 hours and kept the high level at 4-5 hours. A progressive increase of the mRNA expression peaked at 5 hours; the expressions in both groups of carotid catheters blooddrawing increased compared with normal control group, and remained stable after 3 hours compared with the Tail-cut Blooddrawing Group. Conclusion： L-sclectin expressions changed little in tail-cut blooddrawing rats, while carotid catheters resulted moderate or sever trauma. Therefore, it was suggested that it should not be set as hemorrhagic shock control model. As neutrophil L-selection expressions increased after trauma, the adhesion of leucocytes to the venule wall may be beneficial to the healing of wound and enhance the ability of anti-infection. The immediate increasing of neutrophil surface L-selectin expressions in this study was likely due to the direct release of Lselectin from cytoplasm granules that do not depend on protein synthesis.

关键词： traumatic L-selectin rat

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