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RISS 인기검색어
- 검색키워드
- 저자 : Zhihui Wen (검색결과 5 건)
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Kai Wen,Baiqing Xiong,Yongan Zhang,Zhihui Li,Xiwu Li,Lizhen Yan,Hongwei Yan,Hongwei Liu 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5
Precipitation characteristics influencing fatigue crack propagation contained matrix precipitate, grain boundary precipitateand precipitate free zone for Al–Zn–Mg–Cu alloys. Over-aging treatment could effectively regulate precipitation and then tobe able to change fatigue crack propagation behavior compared with the peak aging state. In the current work, typical T651and T7651 aging tempers of the alloy were extracted via hardness, electrical conductivity and mechanical properties underone-step and two-step aging treatments. Fatigue crack propagation (FCP) rate under them was tested and correspondingprecipitation characteristics and fracture morphology were observed. The results indicated that fatigue crack propagationresistance for the T7651 temper possessed an obvious improvement on the side of that for the T651 temper, which was alsosupported by fracture appearance, including tearing ridge, tearing dimple and fatigue striation. The precipitation observationshowed that the T651 alloy contained GPI zone, GPII zone and ηʹ phase while the T7651 alloy possessed ηʹ phase and η phase.Compared with the T651 temper, matrix precipitate for the T7651 temper distinctly owed an expanding of size distributionand an enlargement of average size while cuttable phase still remained the dominance for both tempers. Grain boundaryprecipitate and precipitate free zone manifested no obvious difference between the two aging tempers. Cut and bypass mechanismsof dislocation–precipitate interactions were used for explanation and it revealed the reinforced cuttable phase was infavor of enhancing fatigue crack propagation resistance. A theoretical model which directly correlated FCP rate with matrixprecipitate characteristics was employed to calculate FCP rate by substituting quantitative precipitate characteristics and thecalculation results were vaguely consistent with the experimental measurement, which proved its reliability and feasibility.
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Kai Wen,Baiqing Xiong,Yongan Zhang,Zhihui Li,Xiwu Li,Shuhui Huang,Lizhen Yan,Hongwei Yan,Hongwei Liu 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.3
In the present work, the infl uence of various retrogression treatments on hardness, electrical conductivity and mechanicalproperties of a high Zn-containing Al–Zn–Mg–Cu alloy is investigated and several retrogression regimes subjected to a samestrength level are proposed. The precipitates are qualitatively investigated by means of transmission electron microscopy(TEM) and high-resolution transmission electron microscopy techniques. Based on the matrix precipitate observations, thedistributions of precipitate size and nearest inter-precipitate distance are extracted from bright-fi eld TEM images projectedalong ⟨110⟩ Al orientation with the aid of an imaging analysis and an arithmetic method. The results show that GP zonesand η′ precipitates are the major precipitates and the precipitate size and its distribution range continuously enlarge with theretrogression regime expands to an extent of high temperature. The nearest inter-precipitate distance ranges obtained arequite the same and the average distance of nearest inter-precipitates show a slight increase. The infl uence of precipitates onmechanical properties is discussed through the interaction relationship between precipitates and dislocations.
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Yu Wang,Zhihui Li,Baiqing Xiong,Kai Wen,Shuhui Huang,Xiwu Li,Yongan Zhang 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.3
Microstructure evolution of a new high-alloyed Al–Zn–Mg–Cu–Zr–Sc aluminium alloy during two-stage homogenizationprocess was investigated by use of scanning electron microscope, transition electron microscope and high resolution transitionelectron microscope. The results indicate that the morphology and chemical composition of Al 3 (Sc, Zr) particles formedin the fi rst stage were greatly aff ected by heating temperature. With the increase of heating temperature, the morphologyof Al 3 (Sc, Zr) particles transform from cuboidal with evident faceting to spheroidal due to improved Zr diff usivity. MoreZr atoms enrich in the interface of precipitate/matrix forming a thin layer. Moreover, the mean diameter of precipitatesincreases a little bit with the increase of heating temperature, showing very restricted coarsening rate and high thermal stabilityof Al 3 (Sc, Zr) particles. After an appropriate second stage heat treatment (474 °C × 48 h), the intermetallic formed inthe solidifi cation process could dissolve suffi ciently and Al 3 (Sc, Zr) particles still keep very good coherency with Al matrixwithout abnormal growth.
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Jingzhi Li,Ruiqi Feng,Zhihui Wen,Aili Zhang 한국생물공학회 2017 Biotechnology and Bioprocess Engineering Vol.22 No.4
To investigate effects of different pyruvate decarboxylases on isobutanol titers in Saccharomyces cerevisiae, single-gene deletion of the three PDCs genes encoding pyruvate decarboxylases were constructed in this study. In addition, we over-expressed Ilv2, which catalyzed the first step in the valine synthetic pathway, and Bat2, which was the cytoplasmic branched-chain amino-acid aminotransferase that catalyzed L-valine to 2-ketoisovalerate, to increase isobutanol production in the genetically modified strains. Our results showed that knockout of PDC5 were one of the main factors among the three PDC genes for improving isobutanol titers in S. cerevisiae. Additionally, we found that deletion of PDC5 in strain carrying overexpressed ILV2 and ARO10 resulted in 8-fold higher isobutanol productivity as compared to the control strain in micro-aerobic fermentations. Our results also suggested that engineered strain pdc5ΔpILV2 pARO10 generated lower ethanol titers and higher acetate acid titers than the control strain, while the growth rate and glucose consumption rate of engineered strain pdc5ΔpILV2 pARO10 were slightly lower than that of the control strain. Meanwhile, the biomass concentration of pdc5ΔpILV2 pARO10 decreased dramatically than that of the control strain.
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Liu Shuaiqi,Zhu Zhihui,Li Huiya,Zhao Jie,Wen Xin 보안공학연구지원센터 2016 International Journal of Signal Processing, Image Vol.9 No.1
Combined with the shared similarity among multiple source images and depth of field in a camera, a new image fusion algorithm based on nonsubsampled shearlet transform (NSST) domain is proposed. First, NSST is utilized for decomposition of the source images, the low frequency coefficients is fused by weight votes in the structure-driven regions by using shared similarity and depth of field (SSSID), and then apply larger sum-modified-Laplacian (SML) with depth of field to the high frequency coefficients, finally the fusion image is gained after we do the inverse NSST to the fused coefficients. The algorithm can not only preserve the information of the source images well, but also suppress pixel distortion due to nonlinear operations in transform domain. Experimental results demonstrate that the proposed method outperforms the state-of-the-art transform domain fusion methods on image quality and objective fusion criteria.
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