Si对无压浸渗SiCp/Al复合材料显微组织与热导率的影响

研究了Al-8Mg基体中添加Si对无压浸渗SiCp/Al复合材料显微组织和热导率的影响.结果表明,Si能够改善Al与SiC的润湿性,减少复合材料孔隙度,抑制界面反应,提高相对密度.不含Si时,Al与SiC界面反应严重,并且润湿性较差,导致复合材料的热导率和相对密度较低;当基体中添加质量分数12%的Si时,界面反应受到完全抑制,热导率取得最大值;进一步提高基体中Si含量,由于铝基体的热导率随Si含量的增加而降低,导致复合材料的热导率也随之降低.     

微米和亚微米SiCp增强Al基复合材料的力学性能

为探讨不同尺度SiCp对SiCp /Al复合材料力学性能的影响,对亚微米和微米SiCp增强Al基复合材料的抗拉和抗压等力学性能进行研究.结果表明:SiCp/Al复合材料具有良好的塑性,伸长率随SiCp体积分数和尺寸的增加而减小;其抗拉强度和抗压强度随SiCp体积分数的增加而增加.亚微米SiCp/Al的拉伸和压缩性能均优于微米SiCp/Al.亚微米SiCp /Al复合材料的断裂机制为SiCp/Al界面处空洞的形成及其在基体内扩展.微米SiCp/Al存在 SiCp的解理断裂及其沿基体扩展的复合过程.     

颗粒失效对SiCp/Al复合材料强度的影响

建立复合材料屈服强度综合模型用于分析研究增强颗粒断裂和基体与颗粒的界面脱粘对SiCp／Al复合材料强度的影响;用Eshelby等效夹杂理论分析SiCp/Al复合材料受载时作用在SiC颗粒上的应力,并假设SiC颗粒失效符合Weibull分布,在综合考虑复合材料各种强化机制的基础上引入颗粒断裂和界面脱粘对材料屈服强度的影响,建立SiCp／Al复合材料的屈服强度模型并对模型进行解析。研究结果表明：SiCp/Al复合材料屈服强度随着SiC颗粒含量增加而增加;当颗粒粒度为微米级时,屈服强度随着粒度的减小而增加;在屈服状态下,当颗粒粒度较小时,复合材料的颗粒失效以界面脱粘为主;随着粒度的增大,颗粒的断裂分数迅速增大,颗粒失效则转变为由颗粒断裂和界面脱粘共同控制。     

基于原位合金化的SiCp/Al复合材料等离子弧焊接

为了抑制SiCp/Al基复合材料在焊接过程中的界面反应,补充烧损元素,同时原位产生新的增强颗粒,分别以Al-Ti-Si和Al-Ti-Mg两种药芯焊丝作为填充材料,向熔池中直接添加Al,Si,Ti和Mg等金属元素,用氩氮混合等离子气对SiCp/Al基复合材料进行等离子弧原位焊接.对比分析了两种药芯材料对焊缝组织和性能的影响.结果表明:以两种药芯焊丝作为原位反应填充材料进行等离子弧原位焊接时,均可以有效抑制针状脆生相Al4C3的生成,形成了稳定熔池,得到了以TiC,TiN,AlN,Ti5 Si3,MgAl2O4和细小棒状的Al3Ti等新生增强相的焊缝;焊缝组织致密结合良好,最大抗拉强度分别为232和196 MPa.     

SiC颗粒表面改性对SiCp/Fe烧结及性能的影响

文章通过试验初步探讨了SiC颗粒表面改性对SiCp／Fe复合材料的烧结机制、机械性能及断裂情况的影响．研究表明,在碳化硅复合材料表面化学镀一层镍,能够较好地改善增强体与基体的界面结合,使得碳化硅复合材料的抗弯强度、冲击韧性及宏观硬度均有了明显的提高．     

Si02对Al-Zn-Si合金直接熔融氧化的影响

通过热质量分析试验，研究了在高温空气中的熔融Al-Zn-Si合金表面覆盖Si02引发剂对铝合金直接氧化生长过程的影响．研究结果表明：Si02能显著缩短Al-Zn-Si合金直接熔融氧化的孕育期及A12O3／Al复合材料的生长时间，并且有助于AlzO3／Al复合材料以光滑方式进行氧化生长，形成细化胞状晶团，提高组织均匀度和材料的致密度．促进Al2O3／Al复合材料生长的最佳SiO2覆盖量为12mg／cm^2．     

添加元素对反应烧结碳化硅导电特性的影响

研究了Ni、Mo和Al元素对反应烧结碳化硅导电特性的影响．试样通过室温、高温电阻率的测定和显微组织分析，可知在室温与高温下，加入Ni、Mo和Al均可明显降低反应烧结碳化硅的电阻率，随着Ni、Mo和Al加入量的增加，碳化硅的室温电阻率也下降．其中，Ni、Mo对反应烧结碳化硅电阻率的影响比Al大．在烧结过程中，Ni、Mo分别与液态Si反应，并在碳化硅粒子界面处生成Ni     

6066Al/SiCP复合材料的组织特征与阻尼性能

研究了经制粉→混料→真空抽气→热挤压工艺制备的6066Al/SiCp复合材料的组织特征与阻尼性能.复合材料的阻尼特征通过动态机械热分析仪(DMTA)测量,得出了2种不同SiC含量的6066Al/SiCp复合材料及6066Al合金在温度为30～250℃,频率为0.1,1,10和30Hz时的阻尼值.利用扫描电镜、光学显微镜对复合材料组织特征进行了分析,根据组织特征及阻尼数据对复合材料的阻尼机制进行了讨论.结果表明将2～3μm的SiC颗粒加入6066Al中,当SiC含量为7%(体积分数)时,增强的SiC颗粒分布较均匀,与基体结合良好;当SiC含量为12%时,SiC易聚集成团.少量SiC能明显提高6066Al的阻尼能力,尤其是高温阻尼性能;6066Al/SiCp复合材料的高阻尼性能主要是SiC颗粒加入后使位错密度大大增加,基体晶界及基体与SiC颗粒界面的存在使材料在循环载荷下消耗能量所致.     

Mg-Li合金界面结构及合金化效应的第一性原理研究

利用第一性原理中的DFT理论,研究了Mg/Li界面的能量和电子结构,讨论了替位型掺杂的元素Zn、Al、Si、Ca在Mg/Li界面处的作用。结果表明,合金化元素Zn、Si、Al替换界面处Li原子后,均可提高Mg/Li界面的结合能力,使得界面更加稳定。同时,研究了Mg/Li界面体系的总能量、界面面积、电荷密度以及应力-应变曲线,表明了Zn、Si、Al可改善Mg/Li界面的结合能力,它们由强到弱为:Zn,Si,Al。另外还探讨了合金化元素的强化机理。     

不同冷却条件SiCp／ZA—27复合材料界面的TEM观察

主要用透射电子显微技术（TEM）、电子探针显微分析（EPMA）和选区电子衍射技术（SAD）分析了不同冷却条件下SiCp/ZA-27复合材料的界面特征和结构,发现冷却速度明显影响复合材料的界面结构、界面相组成和复杂金属氧化物的分布以及枝晶生长过程的溶质二次分配,且复合材料慢冷时的界面比液淬时的界面复杂得多。复合材料浆液液淬快冷时的界面特征是初生α（Al)相与 SiC颗粒直接机械结合,界面光滑无界面反应产物和中间过渡相及非晶氧化物;电磁搅拌随炉冷却条件下,复合材料界面绝大部分是共晶组织与SiC颗粒直接结合,少部分是由共晶组织／岛状非晶组织／SiC组成;随炉慢冷时的界面主要是由共晶组织／非晶组织／SiC组成,金属基体与SiC直接结合的界面非常少。不同冷却条件制备的复合材料的界面存在不同厚度的非晶组织。根据界面形貌和选区电子衍射花样并结合计算机模拟计算,发现部分界面处存在第三相（如MgAl2O3,Mg6Cu3Al7等相）,合成电子衍射花样表明这些第三相与SiC或基体间无晶体学位相关系。未发现SiC与基体间有晶体学位相关系,说明α（Al)或共晶相在SiC或基体间无晶体学位相关系。未发现SiC与基体间有晶体学位相关系,说明a(Al)或共晶相在SiC表面成核的可能性较小。复合材料浆液水淬后的基体轻微衍射分析得出饱和a(Al)已发生分解反应,由白色稳定的af相和黑色中间过渡相α′及存在于黑色区域中的η相组成,af与a′的晶格常数有微小差异,晶体结构相同,两相具有良好的共格关系。η相与af的位相关系为：[-1-10]α//[-12-10]η,(1-11)a//(0002)η。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with