混合前驱体制备高织构三维C/C复合材料的微观结构及疲劳行为

以乙醇和甲烷为前驱体,采用化学气相渗透工艺制备了三维五向编织C/C复合材料。利用偏光显微技术分析了复合材料的微观结构,考察了复合材料的静态弯曲性能和疲劳行为,研究了不同循环加载周期对复合材料弯曲强度和力学行为的影响。结果表明:采用混合前驱体可成功制备高织构3DC/C复合材料,材料的平均弯曲强度为379.2 MPa,其疲劳极限为静态弯曲载荷的80.3%。加载循环应力后, C/C复合材料的弯曲强度在不同周次均有所提升,循环105周后弯曲强度的增幅达16.8%。材料弯曲承载时的"屈服区"随着循环次数的增加出现先增大后减小的变化趋势,这与材料疲劳过程中纤维与基体、基体与基体的结合状态有关。

织构化Mg掺杂磷灰石型硅酸镧电解质制备、结构及O^(2-)导电性能

以La2O3和SiO2为原料,首先利用固相法合成La2Si2O7和La2SiO5粉体,然后采用共压法成型得到La2Si2O7(含MgO、La2O3)/La2SiO5/La2Si2O7(含MgO、La2O3)三明治结构,进而在高温下通过互扩散反应制备织构化Mg掺杂硅酸镧电解质(La9.33Si5.8Mg0.2O25.8)。以X线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)、能量色散X线谱(EDS)、交流阻抗等测试与表征手段研究合成粉体物相和Mg掺杂硅酸镧电解质的微结构及其O2-导电性能。结果表明:通过高温互扩散和固相反应过程,可制得单相织构化Mg掺杂硅酸镧电解质,其晶粒c轴沿样品厚度方向织构化程度达70%。同时,XRD、拉曼光谱和EDS能谱分析表明:掺杂Mg主要占据结构中Si位;织构化的Mg掺杂硅酸镧电解质在750℃下电导率达3.81×10-3S/cm、活化能为0.71 eV。

Effect of forging on the microstructure and texture of a high Nb containing γ-TiAl alloy

The effect of forging on the microstructure and texture evolution of a high Nb containing Ti-45Al-7Nb-0.3W(at.%)alloy was investigated by X-ray diffractometer(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM).The results show that the as-cast alloy is mainly composed of α_(2)/γ lamellar colonies with a mean size of 70μm,but the hot-forged pancake displays a near duplex microstructure(DP).Kinking and bending of lamellar colonies,deformation twinning and dynamic recrystallization(DRX)occur during hot forging.Meanwhile,dense dislocations in theβphase after forging suggest that the high-temperature β phase with a disordered structure is favorable for improving the hot-workability of the alloy.Unlike the common TiAl casting texture,the solidification process of the investigated as-cast alloy with high Nb content is completely via the β phase region,resulting in the formation of a<110>γ fiber texture where the<110>γ aligns parallel to the heat-flow direction.In comparison,the relatively strong<001>and weak<302>texture components in the as-forged alloy are attributed to the deformation twinning.After annealing,static recrystallization occurs at the twin boundary and intersections,which weakens the deformation texture.

Preparation and mechanical properties of carbon/carbon composites with high textured pyrolytic carbon matrix

Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon （C/C） composites was 1.89 g/cm3 after depositing for 150 h. The microstructure and mechanical properties of the C/C composites were studied by polarized light microscopy, X-ray diffraction, scanning electron microscopy and three-point bending test. The results reveal that high textured pyrolytic carbon is deposited as the matrix of the composites, whose crystalline thickness and graphitization degree highly increase after heat treatment. A distinct decrease of the flexural strength and modulus accompanied by the increase of the toughness of the C/C composites is found to be correlated with the structural changes in the composites during the heat treatment process.

离子束辅助沉积改善铝薄膜的取向生长

高性能的铝薄膜因具有低的声阻抗而广泛应用于声表面波器件的制备。本文运用Ar离子束辅助沉积技术,在64°Y-X切向的铌酸锂基片上成功的制备出(111)高度取向的铝薄膜,并研究了Ar离子的注入角度对薄膜的织构形成的影响。结果表明,薄膜织构度对辅助离子束入射角度非常敏感,在辅助离子束入射角为35°时,薄膜(111)织构最强,电阻率最小,附着力最好,适合于声表面波器件中的应用。

Key R&D activities for development of new types of wrought magnesium alloys in China

Many researchers in China are actively engaged in the development of new types of wrought magnesium alloys with low cost or with high-performances and novel plastic processing technologies.The research activities are funded primarily through four government-supported programs:the Key Technologies R&D Program of China,the National Basic Research Program of China,the National High-tech R&D Program of China,and the National Natural Science Foundation of China.The key R&D activities for the development of new wrought magnesium alloys in China are reviewed,and typical properties of some new alloys are summarized. More attentions are paid to high-strength wrought magnesium alloys and high-plasticity wrought magnesium alloys.Some novel plastic processing technologies,emerging in recent years,which aim to control deformation texture and to improve plasticity and formability especially at room temperature,are also introduced.

Effect Analysis of High Strain Rate and Anisotropy on Tension⁃Compression Asymmetry of Aluminum Alloy 7050

Using the devices of split Hopkinson tension bar(SHTB)and split Hopkinson pressure bar(SHPB),the dynamic tension and compression experiments in three typical forming directions(rolling direction(RD),transverse direction(TD)and normal direction(ND))were carried out at strain rates of 1000,2000 and 4000 s-1,respectively.From the microscopic point of view,the effect of strain rate and anisotropy on tension compression asymmetry of aviation aluminum alloy 7050 was studied by scanning electron microscope(SEM),metallographic microscope and electron backscatter diffraction(EBSD).The results showed that there was obvious asymmetry between tension and compression,especially that the yield strength of the material in tension was higher than that in compression.The asymmetry in the elastic stage of tension-compression was weaker and the asymmetry in the strengthening stage was stronger with the increase of strain rate.At the same strain rate,the changing trend of the flow stress was distinct under different orientations of tension and compression,which was related to the stress direction of the grains.According to EBSD grain orientation analysis and raw material texture pole figure analysis,it was found that the larger the difference in the degree of grain refinement during tension and compression,the larger the macro-flow stress difference.

Mineralogy and textural impact on beneficiation of goethitic ore

The effect of mineralogy and texture on the beneficiation of goethitic ores from two different origins is highlighted. Sample A having 54.47% Fe with 8.57% loss of ignition （LOl） indicates the presence of vitreous and ochreous goethite, martite and microplaty hematite as the major minerals. Sample B contains 56.90% Fe with 14.4% LOI. There is a pisolithic laterite containing vitreous and ochreous goethite, quartz, kaolinitic clay and there is no hematite mineral. The liberated minerals in -150 ＋ 100 μm size class are 74% for Sample A and 37% only for Sample B which shows that the Sample A appears to be more amenable to beneficiate. A concentrate of 46.7% with 63.22% Fe could be recovered from Sample A while subjected to gravity separation followed by wet magnetic separation. The Sample B does not respond to gravity and magnetic separation due to its complex mineralogy. However, calcination of the Sample B followed by magnetic separation gives the encouraging results. Thus, anomalous behaviour of the goethite dominated ores in beneficiation is attributed to the different textural and liberation characteristic.

Series.the university English four, six level of test examination management in institutions of higher education

college English test band 4 and band 6 is a national examination, the examination organization work is particularly important in this article, through combing the examination link, and takes the examination of the foreign affairs college as an example summarizes work experience, and examination work for the future optimization put forward opinions and Suggestions, in order to achieve the purpose of better service for the teaching service for students.

乙醇热解制备C/C复合材料工艺及组织结构研究

以整体碳毡为预制体,无水乙醇为前躯体,N2做为载气和稀释气,在负压条件下,沉积温度为1050~1200°C,采用压力梯度ICVI工艺制备出C/C复合材料制品,采用偏光显微镜、扫描电镜、透射电镜分析材料的组织结构和断口形貌,利用三点弯曲测定了材料的弯曲强度.结果表明：制备的C/C复合材料基体组织结构在1050°C条件下为中织构与高织构并存的组织,当沉积温度上升为1100~1200°C时,热解碳为均一的高织构组织.制备试样的弯曲破坏应力应变曲线及断口形貌分析表明：断裂特征受热解碳与基体界面结合强弱的影响,弯曲断口以纤维断裂、纤维拔出为主,材料具有假塑性断裂特征,并且随着沉积温度的提高,热解碳基体与纤维的界面结合逐渐增强,断裂方式由假塑性断裂向脆性断裂逐渐转变.

Small onion-like BN leads to ultrafine-twinned cubic BN

Nanotwinned cubic boron nitride(nt-cBN) with remarkable hardness, toughness, and stability has attracted widespread attention due to its distinct scientific and industrial importance. The key for nt-cBN synthesis is to adopt an onion-like BN(oBN) nano-precursor and induce phase transition under high pressure. Here, we found that the size change of oBN used greatly affected the mechanical performance of products. With the precursor size decreasing from^320 to 90 nm, the Vickers hardness of nanostructured products improved from 61 to 108 GPa, due to the fact that large oBN nanoparticles possessed more flattened, orderly and graphite-like shell layers, in sharp contrast to the highly wrinkled and imperfect layers in small-diameter nanoparticles, thus resulting in the apparent reduction of ultrafinetwin substructure in the synthetic products. This study reveals that only small oBN precursor could produce complete ultrafine nt-cBN with outstanding performance. A practical route was proposed to further improve the performance of this important material.