超细晶粒W-40%Cu合金的烧结和力学性能

以纳米W,Cu粉末为原料,通过测定H2中热压烧结和无压烧结的收缩动力学曲线,研究了纳米W-40%Cu化学混合粉末的致密化过程.对比了纳米W粉与常规Cu粉(-44μm)的机械混合粉和纳米W-Cu化学混合粉的热压烧结致密化过程.测定了烧结合金在300℃和500℃下高温应力一应变曲线.实验结果表明:采用纳米W-40%Cu化学混合粉末在H2中无压烧结时最大收缩速率对应温度为980℃;1 200℃烧结平均晶粒小于2μm,相对密度为97%.纳米W-Cu化学混合粉在H2热压烧结时最大收缩速率对应温度为930℃;1 200℃烧结合金的平均晶粒为0.5 μm,相对密度为98%.纳米W-Cu化学混合粉热压合金高温抗压强度比纳米W与常规Cu粉的热压合金高.     

纳米钨合金粉末常压烧结的致密化和晶粒长大

高密度合金由于具有密度和强度高、延性好等一系列优异的性能,在军工上被用作动能穿甲弹材料.纳米材料被认为是21世纪应用前景非常广阔的新型材料,采用纳米粉末可望大大细化钨合金晶粒,显著提高合金的强度、延性和硬度等力学性能,因而是制备新型高强韧高密度钨合金的很重要的研究方向.作者采用机械合金化(MA)工艺制备了纳米钨合金复合粉末,研究了纳米钨合金粉末在常压氢气气氛中的烧结致密化和在烧结过程中的W晶粒长大行为.同时,指出了在液相烧结时存在的问题,即W晶粒加速重排、产生晶粒聚集与合并,迅速发生W晶粒长大,在较短时间内液相烧结时,W晶粒尺寸又长大到接近传统高密度合金水平.研究结果表明,MA纳米粉末促进了致密化,使致密化温度降低100～200℃;在一般固相烧结温度时可以得到晶粒粒径为3～5μm的细晶高强度合金.     

SPS烧结温度对93W-4.9Ni-2.1Fe合金微观结构及性能的影响

以高能球磨法制备的93W-4.9Ni-2.1Fe复合粉末为原料,采用放电等离子烧结技术制备93W--4.9Ni-2.1Fe合金,研究了烧结温度对钨合金微观组织及性能的影响.采用扫描电镜对试样的断口进行观察,采用能量色散谱仪对合金的组元进行成分分析.结果表明:①烧结温度对合金的性能有显著的影响,在1 350℃时钨合金的抗拉强度达到一个极大值,为981 MPa,此时钨合金的相对密度和W晶粒的尺寸分别为98.9%和5μm;②当烧结温度达到1375℃时,合金中Ni元素开始挥发,随着温度的快速上升,合金中Ni元素的挥发不断加剧,当烧结温度升高至1425℃时合金中Ni元素已完全挥发;③合金的断裂方式随着烧结温度的升高发生显著的变化,当烧结温度升至1350℃时钨合金的断裂方式由W晶粒界面分离向W-W、W-黏结相界面断裂转变,而当烧结温度超过此温度时钨合金的断裂方式又转变为W晶粒的沿晶脆性断裂;④SPS快速烧结能够有效抑制W晶粒的长大,促进钨合金的细晶强化作用.     

高能球磨纳米镍粉制备块体材料的研究

采用高能球磨法制备了纳米晶Ni粉末,对纳米晶粉末进行预压烧结,获得纳米晶镍块体材料.采用显微分析方法研究了纳米晶粉末和块体材料的显微组织结构.试验结果表明,高能球磨所得镍粉平均晶粒尺寸为10 nm;预压烧结块体的平均晶粒尺寸在100 nm以下;块体相对致密度在烧结温度为0.6Tm时达到最大值.     

放电等离子烧结制备Al-Zn-Mg-Cu纳米晶合金的组织

利用低温液氮球磨和放电等离子烧结工艺制备了块体纳米晶Al-Zn-Mg-Cu合金.采用X射线衍射(XRD)技术分析了材料的晶粒尺寸和微观应变,利用透射电镜(TEM)研究了合金微观组织的演变.结果表明:采用放电等离子烧结法制备的7000系纳米铝合金具有两种不同的纳米晶结构,以晶粒尺寸50～100nm的等轴晶为主,少量200～400nm的大晶粒为辅;烧结过程中发生再结晶及第二相析出,析出的第二相以η(MgZn2)为主,θ(Al2Cu)以及S(Al2CuMg))为辐.     

纳米W-Cu合金热压收缩动力学曲线特征

采用纳米W-Cu合金粉进行热压烧结,研究热压压力、热压气氛、钨粉粒度对热压烧结收缩动力学曲线的影响,观察和测定合金中钨晶粒的长大,测定部分力学性能.实验结果表明,采用纳米W-Cu合金粉在H2中热压烧结的方法可以在较高压力、很低的烧结温度下制成钨晶粒的超细晶粒W-Cu合金,其相对密度可达98.8%,高温500℃的力学性能远远超过常规W-Cu合金.     

添加Cu,Ni改善Ag-W系合金的结构及性能

本文比较了添加和未添加Cu,Ni的Ag-W系合金的性能,指出添加Cu和Ni的Ag-W系合金在浸透烧结过程中形成一个多元系有限固溶相。用电子显微镜观察W-Ni-Cu-Ag合金时,发现除Ag相与W相外,存在一个环形结构物包裹W颗粒。用扫描透视电镜(STEM)和能谱仪(EDS)进行微区分析证实这个固溶相的存在。列出一种含50wt-％W,余为Ag和Cu,Ni的四元合金(简称AW50合金)装配在电器开关DW_9-440及DW_(10)-200上进行通断试验结果。     

W-TiC合金的烧结行为及其显微组织演变

采用粉末冶金方法制备W-TiC合金,研究W-TiC合金的烧结行为,并对合金的显微组织演变进行分析。结果表明:W-TiC合金粉末具有高的烧结活性,合金致密化过程主要发生在1 500~1 800℃,经1 800℃常压烧结120 min后,合金相对密度即达97.5%;当温度提高至1700℃甚至更高温度后,合金显微组织均匀性明显改善;在高温烧结过程中,添加TiC与W形成(W,Ti)C固溶体以及含W,Ti,C和O元素的复合物粒子相,均匀分布在W基体中,有效地抑制了W晶粒长大,提高了合金性能;在1 950℃烧结120 min后,其相对密度为98.1%,显微硬度达最大值HV670.4,相对纯W提高29.3%。     

Ni-W/ZrO2纳米复合镀层耐高温氧化性能分析

对Ni—W合金镀层及Ni—W／ZrO2纳米复合镀层的耐高温氧化性能进行了分析．热质量和差示扫描量热试验表明，纳米复合镀层氧化增加的质量仅为合金镀层的1／2，纳米ZrO2微粒的加入使Ni—W／ZrO2复合镀层的结构发生变化，其高温热稳定性较Ni—W合金提高39℃．考察了2种镀层在800℃下的氧化增质量，通过扫描电镜观测了镀层氧化后的形貌．实验证明，Ni—W／ZrO2纳米复合镀层的耐高温氧化性能优于Ni—W合金镀层．     

纳米晶W-Ni-Fe复合粉末烧结过程中的致密化与显微组织演变

采用溶胶喷雾干燥-热还原法制备纳米晶93W-4.9Ni-2.1Fe复合粉末,利用高温热膨胀仪测定和研究纳米品复合粉末的烧结收缩动力学曲线特征,计算纳米晶W-Ni-Fe复合粉末的固相烧结激活能,并利用金相显微镜和扫描电镜分析致密化过程中显微组织的演变规律.研究结果表明:纳米晶W-Ni-Fe复合粉末的开始收缩和剧烈收缩温度分别为900℃和1 120℃,其最大的线收缩率达0.097 ％/℃;在1 200℃以下的固相烧结阶段,压坯便发生显著的致密化,其致密化程度可达98％以上,固相烧结的表观激活能为154.83 kJ/mol,比传统粉末烧结激活能大大降低;在固相烧结期间,W晶粒尺寸长大缓慢,在1 380℃以上液相烧结时W晶粒长大急剧加快.     

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.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

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.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

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