应变影响下单晶Ge薄膜热导率分析

利用非平衡态分子动力学模拟方法研究了应变对Ge薄膜热导率的影响。结果表明系统应变对单晶Ge薄膜热导率产生明显影响,热导率随着拉伸应变的增大而减小,随着压缩应变的增大而增大,得出声子速率降低以及薄膜表面重构是产生该模拟结果的内在原因。同时,采用修正的Callaway模型对NEMD结果进行理论验证,两种方法得到的结果吻合得较好。理论结果表明应变弛豫时间对Ge单晶薄膜的热导率产生了重要影响。     

应变影响下单晶Ge薄膜热导率分析（英文）

利用非平衡态分子动力学模拟方法研究了应变对Ge薄膜热导率的影响。结果表明系统应变对单晶Ge薄膜热导率产生明显影响热导率随着拉伸应变的增大而减小,随着压缩应变的增大而增大,得出声子速率降低以及薄膜表面重构是产生该模拟结果的内在原因。同时,采用修正的Callaway模型对NEMD结果进行理论验证,2种方法得到的结果吻合得较好。理论结果表明应变弛豫时间对Ge单晶薄膜的热导率产生了重要影响。     

非平衡等离子体运输系数的数值分析

利用Chapman-Enskog方法计算了非平衡氩等离子体的运输系数及压力、温度和电子-重离子温度系数θ的影响规律.电子和重粒子被视为两种不同气体,并利用广义Saha公式计算等离子体成分.结果表明,非平衡态等离子体运输系数与平衡态相比有较大差别,因而对于非平衡态等离子体若采用平衡态的运输系数计算会造成较大误差.     

纳米银浆料烧结机理及导热性能分子动力学仿真

针对纳米颗粒的烧结机理不明确及烧结过后热导率显著下降等问题进行探究.利用分子动力学仿真的方法，通过热导率的计算验证了势函数选取的正确性，模拟了银纳米颗粒的烧结过程，观察了烧结过程中微观结构的变化，得到了烧结颈生长长度与烧结时间拟合关系，并计算了烧结颈处声子热导率变化情况，最后通过透射电子显微镜观察到试验烧结纳米银颗粒具备与仿真结果相同的五重孪晶结构.结果表明，五重孪晶为纳米颗粒烧结后的稳定结构，纳米颗粒烧结过程中烧结颈生长长度与时间成幂函数关系，烧结颈处微观结构使纳米银的热导率降低了4.42%.     

Zn-Mg合金中两种不同共晶组织竞争生长机理的分析

通过OM、SEM、XRD研究了Zn-Mg合金在3种成分不同冷却条件(薄壁、厚壁)下的凝固组织,探讨了Zn-Mg合金中两种共晶组织的形成机理。结果表明:Zn-2%Mg,Zn-3%Mg和Zn-5%Mg合金中均存在两种共晶结构的竞争生长,分别是非平衡态的EU1(α-Zn/γ-Mg Zn_2)和平衡态的EU2(α-Zn/β-Mg_2Zn_(11))。当冷却速率较大时,倾向于析出平衡态EU2(α-Zn/β-Mg_2Zn_(11))的共晶组织,且平衡态EU2的共晶组织为层片(棒状)的规则的共晶胞形态,宏观下的结构为台阶柱状式;当冷却速率较小时,倾向于析出非平衡态EU1(α-Zn/γ-Mg Zn_2)的共晶组织,且非平衡态EU1的共晶组织为螺旋线型的非规则共晶形态。     

单晶锗薄膜热导率的分子动力学模拟

采用非平衡分子动力学(NEMD)方法研究平均温度为400 K,厚度d=2.8288～11.315 nm的单晶锗薄膜法向的热导率.模拟结果表明,单晶锗薄膜热导率随薄膜厚度的增加以接近线性的规律增加,其数值明显低于同等温度下体态锗的试验值.当薄膜厚度一定时,单晶锗薄膜的热导率随温度增加变化幅度很小,与同体态锗热导率随温度的变化规律相比表现出明显的尺寸效应.     

淬火装置中喷风管路气流计算

设计了一种喷风管路,用毕托管测量了气体实际出流速度,根据管道模型进行了水力学计算,同时还利用Fluent软件进行了相同条件下的数值模拟计算。两种计算方法得到的结果和实验结果比较得出,所研究的管路能满足工程上均匀出流的条件,水力学和Fluent数值模拟两种计算方法得到了相互验证,可以作为将来设计管路的依据。     

板坯连铸过程二冷边界条件处理方法的对比

以相同的冷却强度、拉速、浇注温度、钢种等板坯连铸条件为模拟初始参数,采用相同的凝固潜热处理方式,针对两种常用的板坯连铸二冷边界条件处理方法FCA法和MCA法,分别采用四种不同的传热经验公式,计算了板坯连铸的热过程。得到这两种处理方式四种不同二冷传热经验公式的八组计算结果,并将计算结果与实测值相比较,结果证明,采用FCA法处理边界条件,得到的模拟计算结果与实测值相对误差均小于5%,而利用MCA法处理边界条件,得到的模拟计算结果与实际测量值相对误差在8%左右。因此,采用FCA法处理板坯连铸二冷边界条件得到的模型能更加准确地模拟板坯连铸的热过程。     

非平衡态热力学分析

为了研究非平衡态热力学理论在具体的冶金过程中的应用，本文用该理论模拟计算了转炉的炼钢过程,并建立了该过程的数学模型。得到了转炉冶炼过程的脱碳速度表达式、钢液中硅锰含量变化表达式、氧含量变化表达式以及温度变化表达式。用C语言对整个冶炼过程进行模拟,结果表明非平衡态热力学模型能够描述整个冶炼过程主要元素的成分变化和熔池温度变化,对转炉炼钢生产实际的过程控制提供了新的理论和方法。     

铜/锡界面间扩散行为分子动力学模拟

采用分子动力学方法,基于MEAM原子间作用势模型模拟了钎焊过程中固液界面扩散过程,从原子尺度对液态钎料原子向母材金属中的扩散行为进行模拟计算.计算了锡钎料在510 K温度下向母材中的扩散系数.结果表明,当扩散反应达到平衡态时,原子位移平均平方代换与反应时间成线性关系,钎料原子在x与y矢量方向扩散速度相近,且远大于z方向扩散速率.根据爱因斯坦扩散方程计算得到界面反应过程中钎料原子在xyz三个矢量方向上的扩散系数分别为2.03×10-9,2.05×10-9,5.06×10-10 cm2/s.z方向扩散系数模拟值同试验值比较,模拟结果与试验结果吻合一致.     

Thermal conductivity of EB-PVD ZrO2-4 mol% Y2O3 films using the laser flash method

The variation in thermal conductivity and thermal diffusivity of ZrO₂-4 mol% Y₂O₃ coatings deposited onto Inconel substrates by EB-PVD is examined as a function of coating thickness using the laser flash method. The coatings are found to consist of columnar grains with a feather-like microstructure. The thermal conductivities of the coatings are calculated using two methods: the first involves separating the coating from the substrate and measuring the thermal diffusivity directly; the second uses thermal diffusion results from coatings still attached to the substrate and is based on the response function method. The results of both methods are in excellent agreement, and show that the thermal conductivities of the coatings increase with increasing coating thickness. The results also confirm that the double layer method can be used successfully to calculate the thermal conductivities of thin film coatings.     

基于第一性原理的金属导热性能研究

基于第一性原理提出了一种纯金属热导率的高效计算方法。引入常弛豫时间近似,应用密度泛函理论(DFT)与最大局域化Wannier函数(MLWFs)方法求解金属材料的电子热导率,简化了电子热导率的计算流程;在计算声子热导率时,将Birch-Murnaghan状态方程与Debye模型引入Slack方程,提高了声子热导率的计算效率。采用本方法计算了Al、Mg、Zn 3种材料在300~700 K温度范围内的电导率和热导率,计算值与实测值吻合良好,验证了计算方法的准确性。结果表明,材料的电子和声子的结构是影响热导率的关键因素,在金属材料的导热过程中,电子始终发挥着主要的输运作用,并且随着温度的升高,电子热导率占总热导率的比率也逐渐上升。     

Calculating the effective thermal conductivity of gray cast iron by using an interconnected graphite model

A new theoretical model of gray cast iron taking into account a locally interconnected structure of flake graphite was designed, and the corresponding effective thermal conductivity was calculated using the thermal resistance network method. The calculated results are obviously higher than that of the effective medium approximation assuming that graphite is distributed in isolation. It is suggested that the interconnected structure significantly enhances the overall thermal conductivity. Moreover, it is shown that high anisotropy of graphite thermal conductivity, high volume fraction of graphite, and small aspect ratio of flake graphite will cause the connectivity effects of graphite to more obviously improve the overall thermal conductivity. Higher graphite volume fraction, lower aspect ratio and higher matrix thermal conductivity are beneficial to obtain a high thermal conductivity gray cast iron. This work can provide guidance and reference for the development of high thermal conductivity gray cast iron and the design of high thermal conductivity composites with similar locally interconnected structures.     

First-principle study of magnetic,elastic and thermal properties of full Heusler Co2MnSi

In this work, first principles calculation of structural, electronic magnetic and elastic properties of the half-metallic ferromagnetic Heusler compound Co₂MnSi are presented. We have applied the full-potential linearized augmented plane waves plus local orbitals (FP-L/APW+lo) method based on the density functional theory (DFT). For the exchange and correlation potential generalized-gradient approximation (GGA) is used. The computed equilibrium lattice parameters agree well with the available theoretical and experimental data. Elastic constants and their pressure dependence are also calculated. The calculated total magnetization of 5 μ_B is in excellent agreement with recent experiments. We also presented the thermal effects using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. Temperature and pressure effects on the structural parameters, heat capacities, entropy, thermal expansion coefficient, and Debye temperatures are determined from the non-equilibrium Gibbs functions.     

Pb,Zn和Al在熔点附近的导热系数测试

采用数值方法模拟金属的相变过程、得到了一系列不同热系数下的相界面移动，将实测是面移动曲线与理论相界面移动曲线相对比，以此确定被测金属在熔点温度下的导热系数，用此方法测试了Ｐｂ，Ｚｎ和Ａｌ三种金属的导热系数，所得结果与文献数据吻合较好，一雇中用于测量熔点介于Ｐｂ、Ａｌ之间的金属在熔点导热系数。     

钯的反演势的构建与研究

以面心立方金属钯为研究对象,基于第一性原理中的局域密度近似理论(LDA),计算了不同晶格长度下的原子间内聚能并得到其原子内聚能曲线.通过陈-莫比乌斯晶格反演势理论,得到了精确的反演对势曲线.采用不同势函数对该曲线拟合,通过对拟合效果的对比和分析,提出了全局精度较高的双指数型势函数.同时,分别采用第一性原理方法,原子嵌入势(EAM)方法和反演势数据计算了钯的声子谱.比较声子谱曲线发现,曲线的变化趋势是相似的,说明反演势可以合理的反应原子间相互作用.并且反演势方法所需的计算时间明显少于EAM势方法,说明反演势方法在计算量上有明显优势.最后,计算了金属钯的热膨胀系数,弹性模量和格林乃森常数等物理量.计算结果与实验数据基本符合,表明构建的钯的反演势是准确有效的.     

点缺陷对MOX燃料热导率的影响研究

MOX燃料作为快堆燃料重要的候选燃料类型之一，是核燃料闭式循环的关键环节。导热性能是MOX燃料在堆内服役的关键参数，将直接影响快堆的安全性。目前通常只对实测数据进行拟合得到其热导率经验公式，缺乏对不同Pu含量和氧金属比（O/M）的MOX燃料热导率的理论分析。本文基于经典声子热传导理论，通过对MOX燃料在不同Pu含量和O/M下热导率影响因素的分析，研究了不同类型点缺陷对其热导率的影响。研究结果表明，采用声子传导模型可以很好地预测不同成分MOX燃料的热导率。MOX燃料中离子替代型点缺陷造成的质量差和半径差对热导率的影响权重相对较小，而MOX燃料不同O/M比造成的氧空位型点缺陷对热导率的影响权重相对较大。本研究对于不同成分MOX燃料的热导率预测和成分设计具有重要意义。     

Construction and analysis of dynamic solidification curves for non-equilibrium solidification process in lost-foam casting hypoeutectic gray cast iron

Most lost-foam casting processes involve non-equilibrium solidification dominated by kinetic factors, while construction of a common dynamic solidification curve is based on pure thermodynamics, not applicable for analyses and research of non-equilibrium macro-solidification processes, and the construction mode can not be applied to nonequilibrium solidification process. In this study, the construction of the dynamic solidification curve (DSC) for the nonequilibrium macro-solidification process included: a modified method to determine the start temperature of primary austenite precipitation (TAL) and the start temperature of eutectic solidification (TES); double curves method to determine the temperature of the dendrite coherency point of primary austenite (TAC) and the temperature of eutectic cells collision point (TEC); the "technical solidus" method to determine the end temperature of eutectic reaction (TEN). For this purpose,a comparative testing of the non-equilibrium solidification temperature fields in lost-foam casting and green sand mold casting hypoeutectic gray iron was carried out. The thermal analysis results were used to construct the DSCs of both these casting methods under non-equilibrium solidification conditions. The results show that the transformation rate of non-equilibrium solidification in hypoeutectic gray cast iron is greater than that of equilibrium solidification. The eutectic solidification region presents a typical mushy solidification mode. The results also indicate that the primary austenite precipitation zone of lost-foam casting is slightly larger than that of green sand casting. At the same time, the solid fraction (fs) of the dendrite coherency points in lost-foam casting is greater than that in the green sand casting.Therefore, from these two points, lost-foam casting is more preferable for reduction of shrinkage and mechanical burntin sand tendency of the hypoeutectic gray cast iron. Due to the fact that the solidification process (from the surface to center) at primary austenite growth area in the lost-foam cylinder sample lags behind that in the green sand casting,the mushy solidification tendency of lost-foam casting is greater and the solidification time is longer.     

烧结助剂Y2O3和Pr6O11对Al2O3陶瓷相对密度和热导率的影响

采用高分子网络法制备混合纳米粉体,研究稀土氧化物Y2O3和Pr6O11加入量对Al2O3陶瓷相对密度和热导率的影响。采用阿基米德方法测定样品的体积密度,利用激光脉冲法测量试样的热扩散率并计算得出热导率。结果表明:两种添加剂都可以降低Al2O3陶瓷的烧结温度,提高Al2O3陶瓷的热导率,其中Y2O3的促进作用较强;当保温时间相同、烧结温度为1 500~1 650℃时,Al2O3陶瓷的相对密度和热导率都随烧结温度的升高而增大;当烧结温度相同、保温时间为30~120 min时,Al2O3陶瓷的相对密度和热导率也随保温时间的延长而增大。     

Corrosion rates of zinc,zinc coatings and steel in aerated slightly acidic chloride solutions calculated from low polarization data

A method is presented whereby electrochemical corrosion rate parameters can be calculated from low polarization data. Charge-transfer polarization portions are manually separated from the potential responses to current steps and computer fitted to an equation representing the polarization curve by an iterative least squares technique. Although accurate computer curve fitting is achieved, electrochemically calculated mass losses are typically 50–60% higher than solution analysis derived mass loss. By including the metal ion deposition reaction, electrochemically calculated mass losses are lower by between 0 and 20%, but this makes the electrochemical method redundant because metal ion concentrations are required to calculate metal equilibrium potentials. Variations in corrosion rate parameters and possible sources of measurement error are discussed.