挤压对Mg-Zn-Sn-Al合金力学性能和腐蚀行为的影响

研究了铸态和挤压态Mg-4.5Zn-4.5Sn-2Al合金的微观组织、力学性能和在质量分数3.5%NaCl溶液中的腐蚀行为.结果表明:铸态合金的平均晶粒尺寸为183μm;而挤压后合金的平均晶粒尺寸降低为9μm.挤压态与铸态Mg-4.5Zn-4.5Sn-2Al合金相比,抗拉强度由209 MPa提高到354 MPa,屈服强度由157 MPa提高到216 MPa,伸长率达到19.6%且呈现明显的韧性断裂特征.静态浸泡腐蚀和电化学实验表明,挤压态合金的耐蚀性明显低于相应的铸态合金.     

挤压温度对Mg-3Zn-2.5Al-2.5Ca合金的微观组织和力学性能的影响

采用金相分析、扫描电镜分析、X射线衍射分析和拉伸测试等方法研究了不同挤压温度对Mg-3Zn-2.5Al-2.5Ca(ZAC333)合金的微观组织和力学性能的影响.结果表明,铸态组织的平均晶粒尺寸为185μm;随着挤压温度从623K降低到523K,由于发生了明显的动态再结晶,合金的平均晶粒尺寸从6.32μm减小到3.36μm.ZAC333铸态合金中沿着晶界分布的半连续Al_2Ca和连续Ca_2Mg_6Zn_3第2相在热挤压过程中也发生了明显的破碎而沿着挤压方向分布.与铸态合金的力学性能相比,挤压态ZAC333合金的力学性能有明显的提高.挤压态合金的抗拉和屈服强度分别从176 MPa和284 MPa提高到292 MPa和334 MPa,而延伸率从18%降低到9%.ZAC333合金性能的改善主要归功于热挤压过程中的动态再结晶细晶强化和第2相粒子破碎而产生细化弥散强化的共同作用.     

挤压变形对AZ31镁合金组织和性能的影响

采用500T挤压机试验研究了挤压变形对AZ31镁合金组织和性能的影响。结果表明，挤压变形AZ31镁合金组织以绝热剪切条纹和细小的α再结晶等轴晶为基本特征。挤压变形可显著地细化镁合金晶粒并提高镁合金的力学性能。随挤压比的增大，晶粒细化程度增加，晶粒尺寸由铸态的d400μm减小到挤压态的d12μm（min）；强度、硬度随挤压比的增大而增大，延伸率在挤压比大于16时呈单调减的趋势。     

微量B对NiAl的显微组织和性能的影响

为了揭示微量B对NiAl的显微组织和性能的影响,利用非自耗电弧炉熔炼了四种不同B含量(0.005,0.02,0.05,0.15,质量分数,%)的NiAl-B合金.NiAl-B合金的铸态组织均由单相NiAl组成,且随着B含量的增加,晶粒横向尺寸由约200μm减小到约50μm.B改善了NiAl合金的室温压缩塑性,四种合金的室温压缩塑性均达到6%左右.合金的硬度和压缩屈服强度随着B含量的增加而升高,其中,压缩屈服强度由纯二元NiAl的249 MPa升高到B含量为0.15%时的491MPa.合金强度和硬度的升高起因于B的固溶强化和晶粒细化.     

Mg，Ca元素对可降解Zn合金组织性能影响

采用X射线衍射、扫描电子显微镜、光学显微镜、室温拉伸和浸泡失重法研究了挤压态纯Zn和Zn-0.2Mg-xCa(x=0,0.06,0.15,0.3)(质量分数)合金微观组织、力学性能和体外降解速率.结果表明:200℃挤压后,纯Zn晶粒尺寸达到100μm;Zn-0.2Mg-xCa合金中晶粒尺寸均维持在15~20μm之间,并存在第二相Mg₂Zn₁₁和CaZn₁₃.随着Ca含量增加,CaZn₁₃含量逐渐增加,且当Ca质量分数达到0.15%以上时CaZn₁₃尺寸达到15~50μm.纯Zn的屈服强度和延伸率分别为64MPa和14%,Zn-0.2Mg-xCa合金随着Ca含量增加屈服强度由180MPa提高到约200MPa,延伸率则逐渐由18%降低到6%.纯Zn和Zn-0.2Mg-xCa合金在SBF溶液中降解速率维持在0.05~0.15mm·a^-1,而且随Ca的添加降解速率略有降低.     

TiN晶体尺寸与其力学性能的第一性原理研究

 纳米多晶体材料因其独特的力学性能而成为当前材料科学领域的研究热点之一,尤其是晶粒尺寸对其力学性能的影响倍受关注。本文采用基于密度泛函理论的第一性原理方法,模拟计算了晶粒尺寸为0.6387—2.332nm的TiN的力学性能,得到应力应变关系及屈服强度。计算结果表明,随着晶粒尺寸的增加,TiN的屈服强度降低,晶粒呈现软化趋势。通过对应力-应变曲线分析可知：TiN在应变5%处开始屈服,其屈服强度大约为21.5GPa;抗拉强度发生在应变约为15%时,且随着晶粒尺寸的增加,抗拉强度降低。本文对照了屈服极限的计算值和有限元方法的拟合值,讨论了实验中TiN表面的微观结构与硬度、弹性模量的关系。研究表明,TiN试样中的缺陷对其硬度和强度有很大影响。     

Mg-6Al-1Sn合金板材的微观组织与力学性能

通过对Mg-6Al-1Sn合金(AT61)进行挤压以及后续的单道次大应变量轧制变形,获得了高强塑性的新型变形镁合金板材.组织分析表明AT61合金中主要析出相为Mg17Al_(12)相和Mg2Sn相,挤压态合金经轧制之后晶粒都被细化,合金强度显著提高.随着应变量的增加,晶粒尺寸先显著降低后有所上升,屈服强度变化规律与晶粒尺寸变化规律一致.经过250℃下的单道次约56%大应变量轧制变形后晶粒尺寸细化最明显(约为4.18μm),合金的屈服强度约为196 MPa,抗拉强度约为294 MPa,延伸率约为26.7%,表现出最优的综合力学性能.     

底材厚度对铝热反应熔化制备的块体纳米晶Fe3Al材料的组织和性能的影响

通过铝热反应熔化方法在厚度为5~15 mm的铜底材上制备块体纳米晶Fe3Al材料.通过X射线衍射(XRD)研究材料的晶粒尺寸,研究材料室温压缩下的力学性能和硬度.结果表明,所制备材料的晶粒尺寸均约为20nm,且晶粒尺寸随底材厚度的增加而增加.底材厚度为5 mm时纳米晶Fe3Al材料的屈服强度和硬度具有最大值,随着底材厚度的增加,屈服强度和硬度急剧减小,最后趋于稳定.5 mm时纳米晶Fe3Al材料的屈服强度约是10mm时的1.5倍.     

热处理对四代核电用镍基合金薄壁管组织与性能的影响

利用热力学计算软件JMatPro分析了钍基熔盐堆用Ni-Cr-Mo系高温合金GH3535相析出的热力学及动力学特征,研究了不同热处理制度对冷轧态GH3535合金无缝管的晶粒尺寸及其均匀性、碳化物析出特征、硬度、拉伸性能等的影响规律,观察了不同热处理制度下合金拉伸断口的微观形貌,分析了GH3535合金的拉伸断裂机制.结果表明:在900~1500℃之间,GH3535合金的平衡析出相为富Mo的M6 C型碳化物,M6 C相在固液两相区时便已经开始形成,M6 C相析出所对应的鼻尖温度为1200℃;固溶温度低于1200℃时,合金晶粒尺寸缓慢长大,当固溶温度提高到1230℃,晶粒出现快速长大,平均晶粒尺寸达到160μm;1180℃保温10 min,合金晶粒尺寸的均匀性较好.随着固溶温度升高,合金强度降低、延伸率增加,GH3535合金的拉伸断裂机制为微孔聚集型.     

退火工艺对AZ31B镁合金铸轧板组织和性能的影响

研究不同退火温度、时间对普通铸轧和复合能场(电磁场+超声波)铸轧AZ31B镁板组织及性能的影响。研究结果表明:铸轧镁板的再结晶温度在复合能场作用下降低了约50℃;250℃退火时,普通铸轧镁板无明显再结晶,复合能场铸轧镁板局部再结晶;在300℃,4 h时,铸轧镁板均充分再结晶,复合能场铸轧镁板晶粒细小,组织均匀,平均晶粒直径为8~13μm,而普通铸轧镁板晶粒平均晶粒直径为14~19μm;400℃退火时,晶粒开始粗大,1 h时复合能场铸轧镁板与普通铸轧镁板的平均晶粒直径分别为28~33μm和20~25μm。退火后,铸轧镁板内析出相数减少,复合能场铸轧镁板析出相弥散分布在晶界上,普通铸轧镁板析出相较多并富集在晶界和晶界附近。退火后铸轧镁板的塑性变形能力明显改善,在300℃,4 h时,复合能场铸轧镁板的硬度、抗拉强度、屈服强度、伸长率比普通铸轧镁板分别提高了4.7%,17.2%,34.1%和74.6%。     

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.     

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     

Journal of Donghua University ( English Edition) Contents of Volume 31

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