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1.
挤压铸造可细化Zn-Al43型合金的铸态组织、减轻枝晶偏析,大幅度提高其力学性能,抗拉强度提高40~80%(100~150MPa),延伸率提高至10%以上,合金的耐磨性亦进一步提高,挤压铸造对合金组织的影响与凝固冷却速度的加快以及合金的平衡凝固温度升高有关。合金塑性、韧性显著改善的首要原因是枝晶间显微缩孔的消除,而合金强度的提高则主要是过饱和固溶体中的脱溶过程导致沉淀硬化与分散硬化的结果。  相似文献   

2.
研究了挤压铸造过程中机械振动对A356铝合金材料显微组织与力学性能的影响规律,并对机械振动击碎枝晶的作用机理进行了阐述。结果表明:施加机械振动能够有效地消除材料缩松缩孔及断面裂纹,减少甚至消除挤压铸造铝合金铸锭的微观孔洞,细化晶粒组织,使得组织更加均匀;挤压铸造凝固初期,机械振动能够在很大程度上破碎二次枝晶臂,增加材料的形核率;试验值与理论值的对比分析表明,Kirkwood模型具有更高的精度;机械振动能够提高材料的力学性能,相较于重力铸造与无振动挤压铸造而言,所得铸件的抗拉强度与延伸率均有一定提高.  相似文献   

3.
探讨了晶粒度为ASTM 3~5级的细晶铸造IN718C合金的显微组织对持久性能的影响.通过分析细晶材料的持久断口和显微组织,发现该合金与普通铸造材料不同的是 细晶材料的持久断裂主要为沿晶断裂形式,其碳化物、Laves相和tex0\delta$相主要分布在晶界; 细晶材料在不同铸态枝晶组织中晶界上碳化物和Laves相都有降低材料持久性能的倾向.  相似文献   

4.
深过冷Cu-20Wt%Pb亚偏晶合金的凝固行为   总被引:1,自引:0,他引:1  
采用熔融玻璃净化和循环过热相结合的方法,使Cu-20wt%Pb亚偏晶合金获得了208K的深过冷,在宽过冷范围内研究了Cu-Pb亚偏晶合金的组织演化规律。结果表明,过冷合金熔体初生相为α(Cu),在0~146K的过冷度范围内,均有两次再辉现象;在183~208K的过冷范围内,只出现一次再辉。当△T≤98K时,合金凝固组织为粗大枝晶α 枝晶间Pb相;当116K△≤T≤146K时,凝固组织已无明显的枝晶形貌,组织由细密α基体 细小的Pb颗粒组成;当△T≥183K时,凝固组织与中等过冷度下的组织相似,只是Pb相更细小,分布更均匀。当△T≥133K时试样出现裂纹。  相似文献   

5.
液态Fe-10%Sb合金在熔融玻璃净化和自由落体实验条件下,分别达到429K(0.24TL)和568K(0.32TL)过冷度.深过冷并没有改变合金的相组成,快速凝固组织中只有αFe单相固溶体.熔融玻璃净化实验研究发现,αFe枝晶生长速度随过冷度呈指数函数变化.当过冷度△T〈296K时,枝晶生长速度随过冷度增大而升高,并在296K过冷度处达到极大值1.38m/s.若合金过冷度进一步增大,αFe枝晶生长速度则呈现降低趋势.枝晶生长形态演变的主要规律是,小过冷条件下αFe相以粗大枝晶方式生长,而深过冷合金熔体中形成蠕虫状枝晶.溶质截留程度主要取决于实际枝晶生长速度而不是过冷度大小,同时也与冷却速率相关.由于其结晶温度间隔比较宽大,尽管快速枝晶生长显著抑制了溶质偏析,但是Fe-10%Sb合金仍难以实现完全无偏析凝固.  相似文献   

6.
研究了强磁场对Cu-25%Ag(质量分数)合金凝固组织的影响,分析了不同磁场条件对合金凝固组织的作用机理.研究发现,均恒磁场和梯度磁场对合金的凝固组织有重要影响,改变了富Cu枝晶形貌和尺寸,无磁场条件下初生富Cu枝晶分布不均匀,一次枝晶比较长且粗大,枝晶主要以柱状枝晶为主;在12 T磁场条件下,富Cu枝晶分布比较均匀,一次枝晶变短、粗化,枝晶主要以胞状枝晶为主;在负梯度磁场条件下,富Cu枝晶分布不均匀,在试样下部,树枝晶减少,以小平面方式生长的粗大胞晶为主.通过实验研究表明,利用均恒强磁场控制Cu-Ag合金凝固组织,细化晶粒、减小偏析是具有可行性的.  相似文献   

7.
利用扫描电镜、X射线衍射仪和显微硬度计对常压及6GPa高压下凝固的Al-17Zn-1.5Mg合金的组织和显微硬度进行了研究。结果表明,Al-17Zn-1.5Mg合金在常压凝固条件下,由α-A1相和MgZn2相组成,其中α—Al相长成粗大的枝晶,大量针状第二相位于枝晶间位置,相互连接形成网络状。当该合金在6GPa高压下凝固时,枝晶组织显著细化,第二相尺寸减小、数量减少,形态变成点粒状。合金高压凝固后,显微硬度增加了21%。  相似文献   

8.
对A380铝合金进行了挤压铸造成型和传统重力铸造成型,并制得试样.采用偏光显微镜、扫描电镜、定量金相分析、拉伸性能测试等手段,研究在不同压力下挤压铸造A380铝合金的铸造组织和力学性能.结果表明:当压力在0~75MPa范围内时,随着压力的增加,一次枝晶臂尺寸和气孔率得到大幅下降,共晶组织体积分数增加;二次枝晶臂间距减小;针状富铁β-Al5FeSi相尺寸大幅度减小,同时有部分汉字状α-Al8(Fe,Mn)3Si2相生成.当压力在75~100MPa范围内时,压力继续增加对合金组织细化、第二相形貌改善和力学性能提高的作用不明显.挤压铸造试件与重力铸造试件相比,气孔率减小,显微组织细化,力学性能显著提高.当压力为75MPa时,挤压铸造A380铝合金的铸态抗拉强度和伸长率分别比重力铸造提高19%和65%.  相似文献   

9.
Al-La合金不连续枝晶组织形成机理   总被引:3,自引:0,他引:3  
在Al-La合金的自由凝固试样中,发现Al-35%La合金组织形貌的特殊性,其先结晶相Al11La3枝晶沿主干方向成分是不连续的. 为验证这种组织存在的真实性,采用定向凝固方法制备了不同冷却速度下的Al-35%La合金试样,结果显示出定向凝固Al-35%La合金中Al11La3枝晶沿主干方向成分是不连续的. 在此基础上,分析了化学成分与凝固速度对Al-La合金组织的影响,并初步探讨了这种不连续枝晶的形成机理.  相似文献   

10.
在枝晶晶粒的尺度上,从同时满足溶质守恒与热平衡的原则出发,提出了合金凝固过程中等轴枝晶生长的数学模型。该模型由4个相互联系的微分方程组成,可通过计算机求解,为模拟枝晶合金凝固组织的形成过程奠定了初步基础。  相似文献   

11.
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.  相似文献   

12.
何延凌 《科技信息》2008,(4):258-258
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.  相似文献   

13.
王慧 《科技信息》2008,(10):240-240
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.  相似文献   

14.
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.  相似文献   

15.
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。  相似文献   

16.
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.  相似文献   

17.
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.  相似文献   

18.
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-  相似文献   

19.
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-  相似文献   

20.
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  相似文献   

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