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| 1 | Additive Manufacturing of Ceramic Structures by Laser Engineered Net Shaping显示文摘Ceramic is an important material with outstanding physical properties whereas impurities and porosities generated by traditional manufacturing methods limits its further industrial applications. In order to solve this problem, direct fabrication of Al2O3 ceramic structures is conducted by laser engineered net shaping system and pure ceramic powders. Grain refinement strengthening method by doping Zr O2 and dispersion strengthening method by doping Si C are proposed to suppress cracks in fabricating Al2O3 structure. Phase compositions, microstructures as well as mechanical properties of fabricated specimens are then analyzed. The results show that the proposed two methods are effective in suppressing cracks and structures of single-bead wall, arc and cylinder ring are successfully deposited. Stable phase of α-Al2O3 and t-Zr O2 are obtained in the fabricated specimens. Micro-hardness higher than 1700 HV are also achieved for both Al2O3 and Al2O3/Zr O2, which are resulted from fine directional crystals generated by the melting-solidification process. Results presented indicate that additive manufacturing is a very attractive technique for the production of high-performance ceramic structures in a single step. | NIU Fangyong WU Dongjiang MA Guangyi ZHANG Bi | 2015 | Chinese Journal of Mechanical Engineering2015，28，6： | 7 |
| 2 | Investigation of melt-growth alumina/aluminum titanate composite ceramics prepared by directed energy deposition显示文摘Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics with low thermal expansion properties are promising for the rapid preparation of large-scale and complex components by directed energy deposition-laser based(DED-LB)technology.However,the wider application of DED-LB technology is limited due to the inadequate understanding of process conditions.The shaping quality,microstructure,and mechanical properties of Al_(2)O_(3)/Al_(6)Ti_(2)O_(13)(6 mol%TiO_(2))composite ceramics were systematically investigated as a function of energy input in an extensive process window.On this basis,the formation mechanism of solidification defects and the evolution process of microstructure were revealed,and the optimized process parameters were determined.Results show that high energy input improves the fluidity of the molten pool and promotes the uniform distribution and full growth of constituent phases,thus,facilitating the elimination of solidification defects,such as pores and strip gaps.In addition,the microstructure size is strongly dependent on the energy input,increasing when the energy input increases.Moreover,the morphology of theα-Al_(2)O_(3) phase gradually transforms from cellular into cellular dendrite with increasing energy input due to changing solidification conditions.Under the comprehensive influence of solidification defects and microstructure size,the fracture toughness and flexural strength of Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics present a parabolic law behavior as the energy input increases.Optimal shaping quality and excellent mechanical properties are achieved at an energy input range of 0.36-0.54 W*min^(2) g^(-1) mm^(-1).Within this process window,the average microhardness,fracture toughness,and flexural strength of Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics are up to 1640 Hv,3.87 MPa m^(1/2),and 227 MPa,respectively.This study provides practical guidance for determining the process parameters of DED-LB of melt growth Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics. | Yunfei Huang Dongjiang Wu Dake Zhao Fangyong Niu Guangyi Ma | 2021 | International Journal of Extreme Manufacturing2021，3，3： | 2 |
| 3 | Compositional Variability and Mutation Spectra of Monophyletic SARS-CoV-2 Clades显示文摘COVID-19 and its causative pathogen SARS-CoV-2 have rushed the world into a staggering pandemic in a few months,and a global fight against both has been intensifying.Here,we describe an analysis procedure where genome composition and its variables are related,through the genetic code to molecular mechanisms,based on understanding of RNA replication and its feedback loop from mutation to viral proteome sequence fraternity including effective sites on the replicase-transcriptase complex.Our analysis starts with primary sequence information,identity-based phylogeny based on 22,051 SARS-CoV-2 sequences,and evaluation of sequence variation patterns as mutation spectra and its 12 permutations among organized clades.All are tailored to two key mechanisms:strand-biased and function-associated mutations.Our findings are listed as follows:1)The most dominant mutation is C-to-U permutation,whose abundant second-codon-position counts alter amino acid composition toward higher molecular weight and lower hydrophobicity,albeit assumed most slightly deleterious.2)The second abundance group includes three negative-strand mutations(U-to-C,A-to-G,and G-to-A)and a positive-strand mutation(G-to-U)due to DNA repair mechanisms after cellular abasic events.3)A clade-associated biased mutation trend is found attributable to elevated level of negative-sense strand synthesis.4)Within-clade permutation variation is very informative for associating non-synonymous mutations and viral proteome changes.These findings demand a platform where emerging mutations are mapped onto mostly subtle but fast-adjusting viral proteomes and transcriptomes,to provide biological and clinical information after logical convergence for effective pharmaceutical and diagnostic applications.Such actions are in desperate need,especially in the middle of the War against COVID-19. | Xufei Teng Qianpeng Li Zhao Li Yuansheng Zhang Guangyi Niu Jingfa Xiao Jun Yu Zhang Zhang Shuhui Song | 2020 | Genomics, Proteomics & Bioinformatics2020，18，6： | 1 |
| 4 | Microstructure and mechanical properties of melt-grown alumina-mullite/glass composites fabricated by directed laser deposition显示文摘Melt-grown alumina-based composites are receiving increasing attention due to their potential for aerospace applications;however,the rapid preparation of high-performance components remains a challenge.Herein,a novel route for 3D printing dense(<99.4%)high-performance melt-grown alumina-mullite/glass composites using directed laser deposition(DLD)is proposed.Key issues on the composites,including phase composition,microstructure formation/evolution,densification,and mechanical properties,are systematically investigated.The toughening and strengthening mechanisms are analyzed using classical fracture mechanics,Griffith strength theory,and solid/glass interface infiltration theory.It is demonstrated that the composites are composed of corundum,mullite,and glass,or corundum and glass.With the increase of alumina content in the initial powder,corundum grains gradually evolve from near-equiaxed dendrite to columnar dendrite and cellular structures due to the weakening of constitutional undercooling and small nucleation undercooling.The microhardness and fracture toughness are the highest at 92.5 mol%alumina,with 18.39±0.38 GPa and 3.07±0.13 MPa-m1/2,respectively.The maximum strength is 310.1±36.5 MPa at 95 mol%alumina.Strength enhancement is attributed to the improved densification due to the trace silica doping and the relief of residual stresses.The method unravels the potential of preparing dense high-performance melt-grown alumina-based composites by the DLD technology. | Dake ZHAO Dongjiang WU Jing SHI Fangyong NIU Guangyi MA | 2022 | Journal of Advanced Ceramics2022，11，1： | 1 |
| 5 | Pulsed laser welding of thin Hastelloy C-276: High-temperature mechanical properties and microstructure显示文摘 | WU Dongjiang MA Guangyi NIU Fangyong | 2013 | Materials and Manufacturing Processes2013，28，5： | 1 |
| 6 | Investigation on the Cracking Mechanism of Melt Growth Alumina/Aluminum Titanate Ceramics Prepared by Laser Directed Energy Deposition显示文摘Oxide melt growth ceramics(OMGCs)exhibit excellent performance and microstructure stability near their melt-ing point and are expected to become a new structural material for long-term stable service in extremely high-temperature water-oxygen environments.Owing to its unique advantages of high efficiency,flexible manufac-turing,and near-net shaping,laser directed energy deposition(LDED)has become a promising technology for the rapid preparation of high-performance OMGCs.However,owing to the limited understanding of the crack-ing mechanism,the severe cracking problem that hinders OMGCs-LDED towards engineering applications has not been resolved.Alumina/aluminum titanate(Al_(2)O_(3)/Al_(x)Ti_(y)O_(z),A/AT)ceramics are prepared using an LDED system and their cracking characteristics are investigated.Subsequently,numerical simulations are conducted to reveal the dominant factors and influencing mechanisms of the cracking behavior.The results demonstrate that the cracking nucleation process is mainly controlled by solidification defects,whereas the cracking propagation process is determined primarily by both the microstructure and stress level.This study provides a theoretical basis for the development of appropriate cracking suppression methods for OMGCs-LDED. | Yunfei Huang Dongjiang Wu Chengxin Li Weijie Lv Guangyi Ma Cong Zhou Fangyong Niu | 2023 | Chinese Journal of Mechanical Engineering(Additive Manufacturing Frontiers)2023，2，4： | 0 |
| 7 | Laser-assisted grinding of RB-SiC composites:Laser ablation behavior and mechanism显示文摘Laser ablation is an important process during Laser-Assisted Grinding(LAG)of hard and brittle materials.To realize controllable material removal during laser ablation of RB-SiC composites,ablation experiments under different Laser Energy Density(LAED)and LAG experiments are conducted.Evolution rules and mechanism of physical phase,ablation morphology and crack characteristics caused by laser irradiation are investigated.The forces of LAG and Conventional Grinding(CG)are compared.The results show that ablation surface changes from slight oxidation to obvious material removal with LAED increasing,and ablation depth increases gradually.The ablation products change from submicron SiO_(2)particles to nanoscale particles and floccule.High LAED promotes SiC decomposition and sublimation,which leads to the increase of C element.The SiC phase forms corrugated shape in recast layer and columnar shape in Heat Affected Zone(HAZ)at 56 J/mm^(2).The cold and heat cycle leads to formation of fishbone crack.For ablation specimen under 30 J/mm^(2),the grinding force can be reduced by a maximum of 39%and brittle damage region is reduced.The material removal and microcrack generated will significantly reduce the hardness and improve machinability,which can promote grinding efficiency. | Zhigang DONG Wenchao SUN Xintong CAI Feng YANG Yan BAO Renke KANG Dongjiang WU Guangyi MA Fangyong NIU | 2024 | Chinese Journal of Aeronautics2024，37，1： | 0 |
| 8 | Long-read sequencing and de novo assembly of the cynomolgus macaque genome显示文摘Cynomolgus macaques(Macaca fascicularis)belong to the genus Macaca.They are the most widespread nonhuman primate(NHP)and share a common ancestor with humans from about 25 million years ago(Kumar and Hedges,1998).Because of their phylogenetic proximity to humans,macaques are an attractive NHP research model for a wide range of biomedical research(Yan et al.,2011). | Bing Bai Yi Wang Ran Zhu Yaolei Zhang Hong Wang Guangyi Fan Xin Liu Hong Shi Yuyu Niu Weizhi Ji | 2022 | Journal of Genetics and Genomics2022，49，10： | 0 |
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