ICP-AES测定锆合金(Zr-2、Zr-4)中10种微量杂质元素

本法对锆合金中10种微量杂质元素的测定进行了实验研究。取样250mg时,Al、Co、Cu、Mg、Mn、Mo、Ni、Pb、Ti和V测定范围在10—640μg/g之间,回收率在93%—109%之间,相对标准偏差RSD(n=6)在3.9%—7.8%之间。     

氚在锆合金包壳材料中的扩散行为模拟

基于氚扩散基本模型建立了氚扩散行为一维模拟程序,对模拟程序进行了典型实验验证,模拟结果与实验结果符合较好。分析了不同氚浓度、温度分布对锆合金包壳材料中氚的扩散行为的影响。分析结果表明：包壳-芯块间隙内氚浓度的升高会导致进出包壳的氚扩散通量提高,渗透通量增大;由于包壳氧化层相对较低的扩散系数,包壳氧化层的存在对氚渗透有较大的限制作用;温度对氚扩散速率的影响很显著,温度越高,扩散速度越快;锆合金外表面氧化层的相对低温限制了氚渗透出包壳管的速率,温度梯度导致的热致扩散有利于氚向包壳冷测扩散。     

范性形变对NbTi合金超导转变温度的影响

研究了时效热处理的Nb50wt％Ti和Nb46.5wt％Ti合金在经历不同程度最终冷变形后,它们的超导转变温度的变化。研究发现:当最终真应变≥2.5时,NbTi合金(420℃×40h三次热处理)的超导转变温度随最终真应变增加而线性下降。针对该实验结果,本文在理论机制上进行了探讨。     

中子衍射分析时效处理对镍基单晶高温合金相结构的影响

采用φ振荡和φ固定两种数据采集模式的中子衍射实验结果表明较高的时效温度对消除枝晶最有效,微应变(晶粒区域间的变形不协调性)主要存在于γ'相.利用中子衍射结合扫描电子显微镜对合金的微观组织形貌进行了细致观察,给出了时效温度和时间对γ'相的影响状况,超晶格测量发现了γ'相晶粒之间出现的独特取向差.由不同晶面的中子衍射结果判断时效后合金出现了轻微的四方对称性(a < c)畸变,对这种畸变起主要作用的是基体相.实验结果同时证实了不同方向的应变差异,因而为筏化驱动模型的定量 关键词： 单晶高温合金 中子衍射 超晶格 时效处理     

中子衍射法研究单晶镍基高温合金热机械疲劳引起的应力和晶格错配

采用中子衍射法对热机械疲劳后的单晶镍基高温合金样品内部中心点进行了实验测量,数据处理采用了双相叠加峰和单峰分析两种方法,计算得到了样品材料的宏观等效应力、应力偏量、γ相和γ′相的等效应力和晶格错配度等.实验结果表明,两种分析方法得到的宏观等效应力基本一致.在热机械疲劳循环100周出现最大宏观等效应力和应力偏量,此时位错等微缺陷达到饱和,偏离中心点处γ′相应力减小显著;在热机械疲劳开始阶段负错配度明显减小,随循环周次增多基体塑性应变累积又使负错配度以每次81×10^-6的速度逐渐线形增大. 关键词： 中子衍射 单晶高温合金 等效应力 应力偏量     

形变碳纳米管中水的输运行为研究

水分子通过碳纳米管的运输行为对认识生命的新陈代谢活动、海水淡化和纳米运输器件有着重要的参考作用. 本文通过分子动力学的方法研究了水分子通过形变碳纳米管的运输行为, 即椭圆柱状碳纳米管的离心率e对管内水分子输运的影响. 结果发现椭圆柱状碳纳米管的离心率对管内水分子的偶极矩概率分布、径向函数分布和流量有重要的影响作用. 分析认为碳纳米管的形变使管内水分子的偶极矩态及其运输状态发生变化; 同时也发现在一定范围内通过改变碳纳米管的形状能起到分子开关的作用.     

热处理对V-4Ti合金氦的滞留与热解吸行为的影响

钒合金由于其低中子诱导的放射性和良好的高温性能被认为是未来聚变堆很有希望的第一壁和结构材料。因为氦可以通过放电清洗和中子嬗变产生，氦的滞留与热释放行为将是钒合金在聚变堆应用的重要课题。A．V．Veen领导的研究小组用1keV的氦离子注入到10^13-10^14He／cm^2的剂量研究了钒合金的氦俘获和热解吸机理以及预退火处理的影响。两群热解吸峰被发现，他们认为一个对应于氦，空位一杂质链，另一个对应于氦，带有钒合金原有的缺陷，如细小的析出物所俘获。既然钒合金原有的缺陷与退火处理有关，热处理对氦在钒合金中的滞留的影响是可以预期的，并且已被实验所证实。     

形变碳纳米管中水的输运行为研究

水分子通过碳纳米管的运输行为对认识生命的新陈代谢活动、海水淡化和纳米运输器件有着重要的参考作用.本文通过分子动力学的方法研究了水分子通过形变碳纳米管的运输行为,即椭圆柱状碳纳米管的离心率e对管内水分子输运的影响.结果发现椭圆柱状碳纳米管的离心率对管内水分子的偶极矩概率分布、径向函数分布和流量有重要的影响作用.分析认为碳纳米管的形变使管内水分子的偶极矩态及其运输状态发生变化;同时也发现在一定范围内通过改变碳纳米管的形状能起到分子开关的作用.     

Fe-C合金中形变诱导动态相变的蒙特卡罗模拟

采用蒙特卡罗（MC）方法模拟了Fe-C合金在奥氏体-铁素体相变的平衡温度之上的形变诱导动态相变过程.通过建立合适的MC规则,在一个MC模型中同时实现了奥氏体-铁素体相变、铁素体-奥氏体逆相变以及奥氏体动态再结晶过程的模拟.同时,一个基于矢量变换的拓扑模型被嵌入此MC相变模型,用来跟踪由于塑性变形导致的晶粒形貌变化.在此基础上模拟分析了动态相变过程中铁素体的形成特点,讨论了由于相变、逆相变和动态再结晶交互作用所带来的影响. 关键词： 形变诱导动态相变 蒙特卡罗模型 动态再结晶 介观模拟     

含Nb或Ge的锆合金表面氧吸附行为的第一性原理研究

采用基于密度泛函理论的第一性原理方法, 研究了纯锆表面和含Nb或Ge锆合金表面上氧的吸附性质. 结果表明, Nb和Ge对Zr(0001), (1120)和(1010)表面吸附性质的影响各不相同. 根据计算得到的偏聚能结果, Nb和Ge迁移到Zr(0001)表面比迁移到其他两个表面更容易, 而Nb和Ge 都可以降低Zr(0001)表面对氧原子的吸附能力, 因此这两种元素都能抑制锆合金的初始氧化. 进一步的电子结构分析发现, Nb和Ge改变表面对氧原子的吸附能力是通过改变表面d能带的分布来实现的.     

Elastic and plastic deformations of nickel nanowires under uniaxial compression

Using atomistic molecular dynamics simulation with a Sutton–Chen many body potential, we studied the structural evolution and deformation mechanisms of nickel nanowires under homogeneous uniaxial compressions. Nickel nanowires with helical multi-shell structure and fcc-like crystalline structures have been considered. Elastic and plastic behaviors of nickel nanowires under compression were observed and their elastic limits were determined. Our simulations show that the nickel nanowires with helical multi-shell structure have greater yield strength than that of macroscopic solid. Above elastic limit, the plastic deformation of the nanowires shows behavior that is associated with superplasticity. The final atomic structures for the two kinds of nanowires are resemblant crystalline-like.     

The increasing of localized free volume in bulk metallic glass under uniaxial compression

Using transmission electron microscopy and electron diffraction, we have investigated the microstructure of a Zr₅₅Al₁₀Ni₅Cu₃₀ bulk metallic glass under a uniaxial compression until a failure occurs at room temperature. It is shown that the amorphous structure has changed locally in the vicinity of the failure plane after the plastic deformation. An increase in free volume is observed within the localized areas due to the concentration of plastic flow, suggesting that the increasing of local free volume dominates the deformation mechanism of the metallic glass. The effect of free volume on the `serrated flow' behaviour in the stress--strain curves during the uniaxial compression is discussed.     

原位中子衍射研究两相NiTi合金的微力学相互作用和相变机理

NiTi合金的形状记忆效应与其微观结构特征密切相关,中子衍射技术可以在力学加载过程中原位观察块体NiTi合金的相变、晶间应变以及孪晶再取向等演化特征．结合两相NiTi合金宏观应力一应变曲线呈现的四种阶段性变形特征,利用原位中子衍射技术对其变形过程中的微观结构演化进行了分析．奥氏体初始体积份额约22％,在低应变硬化阶段,晶面（110）B2和（002）B19,的应变分别突然减小和增大表明出现了应力诱发马氏体相变,奥氏体体积份额迅速减小,产生了（011）II型孪晶;同时初始马氏体也开始发生再取向,随着应变量的增加,开始出现新的{20i}型马氏体孪晶,这种孪晶引起的应变卸载时不能回复．在高应变硬化阶段孪晶变形起主导作用,衍射峰半高宽变化较小;而在应变硬化饱和阶段则以滑移机制为主,大量位错的产生使衍射峰半高宽显著增加．     

Exploring the compression behavior of HP-BiNbO_4 under high pressure

In the present work, a third form, the so-called HP-BiNbO_4 synthesized at high pressure and high temperature is investigated with the in-situ angle-dispersive x-ray diffraction(ADXRD) measurements under high pressure. We explore the compression behavior and phase stability of HP-BiNbO_4. The structure of HP-BiNbO_4 is first determined. The x-ray diffraction data reveal that the structure HP-BiNbO_4 is stable under pressures up to 24.1 GPa. The ADXRD data yield a bulk modulus K_o = 185(7) GPa with a pressure derivative K_o'= 2.9(0.8). Furthermore, the data are compared with those of other ABO_4 compounds. The results show that the bulk modulus of HP-BiNbO_4(about 185 GPa) is slightly higher than that of tetragonal BiVO_4 and significantly greater than those of the tungstates and molybdates.     

Real‐time Raman spectroscopy measurements to study the uniaxial tension of isotactic polypropylene: a global overview of microstructural deformation mechanisms

Micro‐Raman spectroscopy was used to investigate the main deformation micromechanisms of isotactic polypropylene uniaxially stretched at constant temperature (T = 30 °C) under a constant true strain rate ( = 5.10⁻³ s⁻¹). To accurate measurements namely to be free of the recovering phenomenon which causes in most of the cases interference during post‐mortem analysis, we introduced a new experimental setup combining a Raman spectrometer with a tensile machine piloted by the VidéoTraction™ system. Microstructure is described by essential parameters such as the crystallinity index, the macromolecular orientation both in the crystalline and the amorphous phase, and distribution of the internal stress at the chemical bonds scale. For each, a well‐tried Raman spectral criterion was used. Cross‐checking of these results, obtained with a minimum of tensile tests, allows a more complete understanding of the deformation micromechanisms of semi‐crystalline polymer. Copyright © 2013 John Wiley & Sons, Ltd.     

Atomistic study of temperature and strain rate-dependent phase transformation behaviour of NiTi shape memory alloy under uniaxial compression

Molecular dynamics simulation was conducted to investigate the phase transformation behaviour of nickel–titanium (NiTi, 50%-50% at.%) nanopillar under uniaxial compression at loading rates varying from 3.30 × 10⁷ to 3.30 × 10⁹ s^?1 and at temperatures varying from 325 to 600 K. The phase transformation of NiTi was observed to be sensitive to loading rates and temperatures. The phase transformation stress of B2 → B19 increased with increasing temperature while it was insensitive to loading rate. The phase transformation stress of B19 → B19′ → BCO increased with increasing strain rate and decreasing temperature. In addition, reverse phase transformation was observed during compression due to the interaction between the phase transformation of B19 → B19′ → BCO and the deformation twinning/dislocation slide-induced plasticity of the BCO phase, leading to different residual crystal structures after loading. Moreover, a diagram for the phase transformation behaviour of NiTi in the simulated ranges of strain rate and temperature was obtained, from which the contrary experimental observations on the phase transformation behaviour of NiTi from the studies of Nemat-Nasser et al. (Mech. Mater. 37 (2005) p.287) and Liao et al. (J. Appl. Phys. 112 (2012) p.033515) at various strain rates could be well explained.     

Effects of twin and stacking faults on the deformation behaviors of Al nanowires under tension loading

The effects of twin spacing and temperature on the deformation behavior of nanotwinned Al under tensile loading are investigated using a molecular dynamic(MD) simulation method.The result shows that the yield strength of nanotwinned Al decreases with the increase of twin spacing,which is related to the repulsive force between twin boundary and the dislocation.The result also shows that there is no strain-hardening at the yield point.On the contrary,the stress is raised by strain hardening in the plastic stage.In addition,we also investigate the effects of stacking fault thickness and temperature on the yield strength of the Al nanowire.The simulation results indicate that the stacking fault may strengthen the Al nanowire when the thickness of the stacking fault is below a critical value.     

Al纳米线不同晶向力学行为和变形机制的模拟

采用分子动力学模拟计算方法,考察具有较高层错能的Al纳米线沿不同晶向的力学行为和变形机制。在相同计算条件下与具有较低层错能的Ni、Cu、Au和Ag等FCC金属纳米线进行比较。结果表明：在力学行为方面,Al纳米线的弹性模量呈现明显的结构各向异性,满足E_[111] > E_[110] > E_[100]的关系,这一关系在FCC金属纳米线中普遍成立;Al纳米线的屈服应力随晶向呈现σ_y[100] > σ_y[111] > σ_y[110]的关系,这一关系在具有较低层错能的FCC金属纳米线中不具有普遍性,这与体系中位错形成机制密切相关。根据拉伸变形过程微观结构的演变规律,阐明Al纳米线不同晶向的变形机制,并与具有较低层错能的Ni、Cu、Au和Ag等FCC金属纳米线的变形机制进行比较。结果表明,对于尺度较小的高层错能Al纳米线,Schmid因子和广义层错能均难以准确预测其变形机制。