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Microstructure evolution of eutectic Nb–24Ti–15Si–4Cr–2Al–2Hf alloy processed by directional solidification

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Rare Metals 2017年第6期36卷 472-477页

作者： Zhen li Sai-nan Yuan li-na jia Bin Kong Zhen Hong Hu Zhang School of Materials Science and Engineering Beihang Universtity Beijing 100191 China

In this work, the near-eutectic Nb-24Ti-15Si-4Cr-2Al-2Hf（at%） alloy was directionally solidified at 1900 ℃ with withdrawal rates of 6, 18, 36, 50 mm·min^-1 and then heat-treated at 1450 ℃ for 12 h. The microstructure evolution was investigated. The results show that the microstructure of the directionally solidified（DS） alloy is composed of Nbss＋Nb5Si3 eutectics within the whole withdrawal rate range, while the variation of rates makes a great difference on the solidification routes,the morphology and size of Nb_（ss）＋Nb_5Si_3 eutectic *** the increase in withdrawal rates, the petaloid Nbss＋Nb5Si3 eutectic cells transform into granular morphology. After the heat treatment, a mesh structure Nbssis formed gradually which isolates the Nb5Si3, and the phase boundaries become smoother in order to reduce the interfacial energy. Moreover, two kinds of Nb5Si3 exist in the heat-treated（HT） samples identified by crystal form and element composition, which are supposed as α-Nb5Si3 and γ-Nb5Si3, respectively. This study exhibits significant merits in guiding the optimization of Nb-Si-based alloys＇ mechanical properties.

关键词： Nb-Si-based alloy Directional solidification Heat treatment Microstructure evolution Intermetallic

Oxidation behavior of Nb–24Ti–18Si–2Al–2Hf–4Cr and Nb–24Ti–18Si–2Al–2Hf–8Cr hypereutectic alloys at 1250°C

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Rare Metals 2017年第3期36卷 168-173页

作者： Zhen Hong Hu Zhang Jun-Fei Weng lin-Fen Su Zhen li li-na jia School of Materials Science and Engineering Beihang UniversityBeijing 100191China

Nb-24Ti-18Si-2Al-2Hf-4Cr and Nb-24Ti-18Si-2Al-2Hf-8Cr alloys were prepared by arc melting in a water-cooled crucible under argon *** characteristics and oxidation resistance of the alloys at 1250 ℃ were *** results show that,when the Cr content is 4 at%,the microstructures consist of （Nb,Ti）ss and Nb5Si3;as Cr content increases to 8 at%,C14 Laves phase Cr2Nb is *** isothermal oxidation tests show that the oxidation kinetics of the two alloys follow similar *** weight gains of the two alloys after oxidation at 1250 ℃ for 100 h are 235.61 and 198.50 ***-2,*** oxidation,SiO2,TiO2,Nb2O5 and CrNbO4 are formed at ***,Ti2Nb10O29 is formed after oxidation for 20 min and begins to change into TiNb2O7 as the oxidation ***2 is formed as solid state at first but later evolves into glassy state to improve the cohesion of the *** oxidation for 100 h,oxidation products consist of SiO2,TiNb2O7,Nb2O5 and CrNbO4.

关键词： Nb-Si-based alloy lntermetallics Microstructural characteristics Oxidation

Energy Density Dependence of Bonding Characteristics of Selective Laser-Melted Nb–Si-Based Alloy on Titanium Substrate

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Acta Metallurgica Sinica(English Letters) 2018年第5期31卷 477-486页

作者： Yue-ling Guo li-na jia Bin Kong Yong-lin Huang Hu Zhang School of Materials Science and Engineering Beihang University

Spherical Nb–20Si–24Ti–2Cr–2Al pre-alloyed powders were processed by selective laser melting（SLM） on Ti6Al4V substrates with different energy densities. A series of single tracks and single layers were produced using different processing parameters, including powder size, laser power, scanning speed and hatch distance. Results showed that the pre-alloyed powders ranging from 45 to 75 lm were more applicable to SLM with less balling tendency, in comparison with those between 75 and 180 lm. The increase in linear energy density（LED） resulted in the decrease in contact angle and the increase in the width of single track as well as its penetration depth into the substrate. Smaller hatch distance leaded to a larger remelted part of the former track and a higher volumetric laser energy density. With a thickness of 75.6 lm, an interfacial intermediate layer, enriched in Ti and depleted in Nb, Si, Cr and Al, was formed between the SLM part and the Ti6Al4V substrate. The mechanisms of the elimination of balling phenomenon by employing a higher LED and the interfacial bonding characteristics between Nb–Si-based alloys via SLM and the Ti6Al4V substrate were discussed.

关键词： Nb-Si alloys Selective laser melting Additive manufacture Bonding character Microstructure

QTL analysis of leaf photosynthesis rate and related physiological traits in Brassica napus

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Journal of Integrative Agriculture 2015年第7期14卷 1261-1268页

作者： YAN Xing-ying QU Cun-min li jia-na CHEN li liU lie-zhao College of Agronomy and Biotechnology Southwest University Biotechnology Research Center Southwest University

Rapeseed （Brassica napus L.） oil is the crucial source of edible oil in China. In addition, it can become a major renewable and sustainable feedstock for biodiesel production in the future. It is known that photosynthesis products are the primary sources for dry matter accumulation in rapeseed. Therefore, increasing the photosynthetic efficiency is desirable for the raise of rapeseed yield. The objective of the present study was to identify the genetic mechanism of photosynthesis based on the description of relationships between different photosynthetic traits and their quantitative trait loci （QTL） by using a recombinant inbred line （RIL） population with 172 lines. Specifically, correlation analysis in this study showed that internal CO2 concentration has negative correlations with other three physiological traits under two different stages. Totally, 11 and 12 QTLs of the four physiological traits measured at the stages 1 and 2 were detected by using a high-density single nu- cleotidepolymorphism （SNP） markers linkage map with composite interval mapping （CIM）, respectively. Three co-localized QTLs on A03 were detected at stage 1 with 5, 5, and 10% of the phenotypic variation, respectively. Other two co-localized QTLs were located on A05 at stage 2, which explained up to 12 and 5% of the phenotypic variation, respectively. The results are beneficial for our understanding of genetic control of photosynthetic physiological characterizations and improvement of rapeseed yield in the future.

关键词： Brassica napus photosynthesis quantitative trait loci (QTL)

Runoff Characteristics of the Nen River Basin and its Cause

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Journal of Mountain Science 2014年第1期11卷 110-118页

作者： li Hong-yan WANG Yu-xin jia li-na WU Ya-nan XIE Miao Key Laboratory of Groundwater Resources and Environment Ministry of EducationJilin University

Based on annual runoff data collected from several hydrological stations in the Nen River Basin from 1956 to 2004,the cumulative filter method,Mann-Kendall method and Morlet wavelet analysis were used to analyze variations in the characteristics and factors influencing ***,the general characteristics list as:The distribution of runoff was found to be uneven within a year,and the annual variation showed an overall decreasing *** abrupt change points of runoff were found to be in the early 1960s,middle 1980s and late *** time scales analysis revealed three time-scale cycles,a long-term cycle of about 20-35 years with a scale center of 25 years,another cycle of about 8-15 years with a scale center of 11 years and a short-term cycle of about 5 *** on the Morlet wavelet transform coefficients figure of the 25-year time scale,it is preliminarily estimated that the Nen River Basin will enter a high flow period in *** results obtained using various methods were consistent with each *** physical causes of the results were also analyzed to confirm their accuracy.

关键词： Nen River Basin Runoff changes Morlet wavelet analysis Mann-Kendall test

Microstructures and high-temperature oxidation behavior of directionally solidified Nb-Si-based alloys with Re additions

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Rare Metals 2023年第1期42卷 273-280页

作者： Jie-Chao Zhang li-na jia Jun-Fei Weng lin-Fen Su Bin Kong Hu Zhang School of Materials Science and Engineering Beihang UniversityBeijing100191China

High-temperature oxidation behavior of directionally solidified(DS) Nb-Si-based alloys with Re additions was investigated at 1200 and 1250℃,*** and high-temperature oxidation behavior of the alloys were *** show that the microstructures in vertical section of Nb-24Ti-15Si-4Cr-2Al-2Hf-xRe(x=0,1,3;at%) alloys grow parallel to the withdrawal direction and the cross section exhibits bud-like *** bud-like structures become finer with more Re *** weight gain of the Nb-24Ti-15Si-4Cr-2Al-2Hf-3Re alloy after oxidation at 1200℃ for 100 h is 198.1 mg·cm^(-2),and it is a bit higher at 1250℃.The other two alloys perform somewhat *** influence of Re addition on the oxidation resistance at 1250℃ is more significant than that at 1200 ℃.Although Re addition does not benefit obviously the high-temperature oxidation resistance of the DS samples,it does not compromise the oxidation resistance with a certain amount of Re additions in contrast with the alloy without Re addition.

关键词： Nb-Si alloys Directional solidification Rhenium addition Oxidation behavior Microstructure

Improvement of microstructure and mechanical properties of Al−Cu−li−Mg−Zn alloys through water-cooling centrifugal casting technique

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Transactions of Nonferrous Metals Society of China 2024年第11期34卷 3486-3503页

作者： Qing-bo YANG Wen-jing SHI Wen liU Miao WANG Wen-bo WANG li-na jia Hu ZHANG School of Materials Science and Engineering Beihang UniversityBeijing 100191China Research Center for lightweight Materials Ningbo Institute of TechnologyBeihang UniversityNingbo 315100China Suzhou Laboratory Suzhou 215123China

The microstructure and mechanical properties of as-cast Al−Cu−li−Mg−Zn alloys fabricated by conventional gravity casting and centrifugal casting techniques combined with rapid solidification were *** results demonstrated that compared with the gravity casting technique,the water-cooling centrifugal casting technique significantly reduces porosity,refinesα(Al)grains and secondary phases,modifies the morphology of secondary phases,and mitigates both macro-and *** improvements arise from the synergistic effects of the vigorous backflow,centrifugal field,vibration and rapid *** and coarse plate-like Al13Fe4/Al7Cu2Fe phase result in the fracture before the gravity-cast alloy reaches the yield *** centrifugal-cast alloy,however,exhibits an ultra-high yield strength of 292.0 MPa and a moderate elongation of 6.1%.This high yield strength is attributed to solid solution strengthening(SSS)of 225.3 MPa,and grain boundary strengthening(GBS)of 35.7 *** contributes the most to SSS with a scaling factor of 7.9 MPa·wt.%^(-1).The elongation of the centrifugal-cast alloy can be effectively enhanced by reducing the porosity and segregation behavior,refining the microstructure and changing the morphology of secondary phases.

关键词： Al−Cu−li−Mg−Zn alloy water-cooling centrifugal casting microstructure mechanical properties segregation behavior

High-temperature oxidation behavior of Nb-Si-based alloy with separate vanadium,tantalum,tungsten and zirconium addition

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Rare Metals 2021年第3期40卷 607-615页

作者： Sheng-nan Zhang li-na jia Yue-ling Guo Bin Kong Feng-Xiang Zhang Hu Zhang School of Materials Science and Engineering Beihang UniversityBeijing 100191China

The microstructure and oxidation behavior of directionally solidified(DS) Nb-15 Si-24 Ti-4 Cr-2 Al-2 Hf alloys with separate vanadium,tantalum,tungsten and zirconium additions were investigated by X-ray diffraction(XRD),electron probe microanalyzer(EPMA) equipped with wave-dispersive spectroscopy(WDS),scanning electron microscopy(SEM) and transmission electron microscopy(TEM) equipped with an energy-dispersive spectroscopy(EDS).Results show that the five alloys are all composed of primary(Nb,Ti) solid solution((Nb,Ti)ss)phase and eutectic(Nb,Ti)ss/(Nb,Ti)_(5) S_(3) *** oxidation at 1250℃ for 100 h in air,the surfaces of the five alloys are covered by the oxides of Nb_(2)O_(5),TiNb_(2) O_(7),Ti_(2) Nb10O29,TiO_(2) and amorphous SiO_(2).It is found that the alloying elements of V and W are detrimental for oxidation resistance and the addition of Ta has no obvious *** addition obviously benefits the oxidation resistance at high temperature,by decreasing the weight gain from 242.75 to184.83 mg·cm^(-2).The oxidation mechanism of Nb-Sibased alloys and the effects of different alloying elements on the oxidation resistance of Nb-Si-based alloys were discussed.

关键词： Nb-Si-based alloys Directional solidification Microstructure Oxidation

Microstructure and High-Temperature Oxidation Behavior of Dy-Doped Nb–Si-Based Alloys

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Acta Metallurgica Sinica(English Letters) 2018年第7期31卷 742-752页

作者： Yue-ling Guo li-na jia Hua-Rui Zhang Bin Kong Yong-lin Huang Hu Zhang School of Materials Science and Engineering Beihang University

Microstructures and oxidation behaviors of four Dy-doped Nb-Si-based alloys at 1250 ℃ were investigated. The nominal compositions of the four alloys are Nb-15Si-24Ti-4Cr-2Al-2Hf-xDy （at.%）, where x = 0, 0.05, 0.10 and 0.15, respectively. Results showed that the four alloys all consisted of Nbss, αNbsSi3 and γNbsSi3, and the addition of Dy produced no obvious effect on the phase constitution and the microstructures of Nb-Si-based alloys. After oxidation at 1250 ℃ for 58 h, it was found that the addition of Dy accelerated the oxidation rate of Nb-Si-based alloys and caused a larger weight gain, accompanied by the formation of a more porous and less protective oxide scale. The oxides of Nb2O5, Ti2Nb10O29, TiNb2O7, Ti0.4Cr0.3Nb0.302 and glassy SiO2 were formed on Dy-doped Nb-Si-based alloys. The high- temperature oxidation mechanism of Dy-doped Nb-Si-based alloys was discussed.

关键词： Nb-Si alloy Intermetallics Directional solidification - Oxidation - Microstructure