共查询到19条相似文献,搜索用时 78 毫秒
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为了探索不同合金元素对Nb C异质形核的影响,本文利用第一性原理研究了合金元素X(X=Cr,Mn,Mo,W,Zr,V,Ti,Cu和Ni)对ferrite(100)/Nb C(100)界面性质的影响,并且分析了上述合金元素掺杂前后界面的黏附功、界面能和电子结构.研究结果表明,Cr,V和Ti掺杂的界面具有负的偏聚能,说明它们容易偏聚到ferrite/Nb C界面,但Mn,W,Mo,Zr,Cu和Ni却难以偏聚到此界面.当Mn,Zr,Cu和Ni取代界面处的Fe原子后,界面的黏附强度降低,即这些合金减弱铁素体在Nb C上的形核能力.然而Cr,W,Mo,V和Ti引入界面后,其黏附功比掺杂前的界面要大,且界面能均降低,即提高了界面的稳定性.因此,W,Mo,V和Ti,尤其是Cr,能够有效地促进铁素体形核和细化晶粒.电子结构分析表明,Zr和Cu引入界面后,界面处的Zr,Cu原子和C原子的相互作用变弱;然而Cr和W引入界面后,Cr,W和C原子之间形成了很强的非极性共价键,提高了ferrite/Nb C界面的结合强度. 相似文献
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超高强度马氏体钢的力学性能强烈依赖于逆变奥氏体的形状、尺寸及含量.通常,提高逆变奥氏体含量,有助于改善超高强度钢的塑韧性.对含Cu马氏体淬火钢时效处理时, Cu粒子会在马氏体组织边界沉淀,并作为质点促进逆变奥氏体形核.为了探索不同合金元素对逆变奥氏体在Cu沉淀上异质形核的影响,本文利用第一性原理方法研究了合金元素X (X=Cr, Al, Mo, W, Ni, Co, Mn)对Cu/γ-Fe界面性质的影响,并分析了合金原子替换界面处Cu和Fe原子前后界面的黏附功、界面能和电子结构.研究结果表明,合金元素Cr,Mo, W, Mn替换Cu/γ-Fe界面处Cu原子时, Cu/γ-Fe界面处产生强烈的X—Fe共价键,黏附功增大且界面能减小,显著提高界面稳定性,促进γ-Fe在Cu沉淀上异质形核.而替换界面处Fe原子时,界面稳定性变化很小,掺杂原子与相邻的其他原子成键较弱. 相似文献
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采用分子动力学方法模拟研究了未重构的金刚石/硅(001)面相接触时界面层原子的弛豫过程及所形成的异质界面的结构特征.硅碳二元系统中原子间的相互作用采用Tersoff多体经验势描述.弛豫前沿[110]与[110]方向界面碳硅原子数之比均为3∶2.界面碳硅原子总数之比为9∶4.弛豫后金刚石与硅界面处晶格匹配方式改变为[110]方向基本上以3∶2关系对准,而[110]方向大致以1∶1关系对准.相应地,界面碳硅原子总数之比接近3∶2.界面下方部分第二层硅原子在弛豫过程中向上迁移至界面是引起这种变化的原因,同时该层其他原子及其底下一到两个原子层厚度的区域在[001]方向上出现一定程度的无序化转变倾向.金刚石/硅异质界面处的硅碳原子发生强烈键合,形成平均键长为0.189nm的硅碳键.研究证实,晶格匹配主要呈现界面及其附近硅原子迎合界面碳原子排列的特点.
关键词:
金刚石
硅
异质界面
分子动力学 相似文献
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以亲水性微观粗糙表面上不同几何形貌及分布的微柱阵列为对象, 讨论了液滴在亲水性粗糙表面上的润湿过程以及润湿状态的转变阶段. 从能量角度分别考察了微观粗糙结构几何形貌及分布、微柱几何参数、固体表面亲水性、接触角滞后作用等因素对液滴润湿状态转变的影响规律. 研究发现: 在亲水粗糙表面, 正方形微柱呈正六边形阵列分布时, 液滴更容易形成稳定的Cassie状态, 或者液滴仅发生Cassie状态向中间浸润状态的转变; 与此同时, 减小微柱间距、增大方柱宽度或圆柱直径、增大微柱高度、增强固体表面的亲水性将有利于液滴处于稳定的Cassie状态, 或阻止润湿状态向伪-Wenzel或Wenzel状态转变; 然而, 当液滴处于Cassie状态时, 较小的固-液界面面积分数或减弱固体表面亲水性能均有利于增大液滴的表观接触角, 因此在亲水表面设计粗糙结构时应综合考虑润湿状态稳定性和较大表观接触角两方面因素; 此外, 接触角滞后作用对于液滴状态的稳定性以及疏水性能的实现具有相反作用的影响. 研究结果为液滴在亲水表面获得稳定Cassie状态的粗糙结构设计方法提供了理论依据.
关键词:
亲水表面
微观粗糙结构
表面自由能
润湿状态转变 相似文献
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The structural and chemical properties with non-isothermal crystallization kinetics of PET–ZnO nanocomposites have been reported in this article. ZnO nanoparticles have been synthesized via chemical route with average diameter 19 nm which made confirm by transmission electron microscopy and X-ray diffractometer (XRD) techniques. PET–ZnO nanocomposites have been prepared by solution casting method. The structural and chemical changes occurred in poly (ethylene terephthalate) after inclusion of ZnO nanoparticles have been studied with the help of XRD and Fourier transform infrared spectroscopy, respectively. It was observed from differential scanning calorimeter that ZnO nanoparticles work as nucleating agent for heterogeneous nucleation in PET matrix under non-isothermal crystallization process. The combined Avrami and Ozawa models have been proved adequate to explain non-isothermal crystallization kinetics of PET–ZnO nanocomposites, and also, ZnO nanoparticles have been caused to reduce crystallization activation energy in pristine PET as per the applied Kissinger model. 相似文献
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Satinath Ghosh 《Molecular physics》2013,111(7):868-877
Density functional theory has been applied to investigate the vapor to liquid heterogeneous nucleation on a flat solid surface, by invoking a model free energy density functional along with an exponential density model. The effects of supersaturation of the vapor and the strength of the solid-fluid interaction on the nucleation barrier have been investigated for Lennard–Jones fluid with 12–6 fluid–fluid and 9–3 solid–fluid interaction model. The spinodal decomposition of vapor has been observed at higher supersaturation or at higher strength of the solid–fluid interaction. The shape, density profile and the free energy of formation of droplets of any arbitrary size have been obtained in this work. 相似文献
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An angular cutoff composite model for investigation on electromagnetic scattering from two-dimensional rough sea surfaces 下载免费PDF全文
Based on the local configuration angle division to select the corresponding method for electromagnetic scattering calculation from rough sea surface,this paper presents an angular cutoff composite model:when the local scattered angle is in the specular region that is given by an approximately 20 degrees cone around the specular direction,the Kirchhoff approximation is applied to evaluate the specular reflection,which dominates the total scattering in this region;the small perturbation method is employed to handle the diffuse reflection which is predominant as the local scattered angle is situated out of the specular region.Numerical results are compared with those of experimental and theoretical models in several configurations as a function of incident angle,wind speed,wind direction.The comparison of numerical results of other experimental and theoretical models in several configurations shows that the new composite model is robust to give accurate numerical evaluations for the sea surface scattering. 相似文献
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A.R. Massih 《哲学杂志》2013,93(31):3961-3980
A model for nucleation of second phase at or around a dislocation in a crystalline solid is considered. The model employs the Ginzburg–Landau theory of phase transitions comprising the sextic term in the order parameter (η6) in the Landau free energy. The ground state solution of the linearised time-independent Ginzburg–Landau equation is derived, through which the spatial variation of the order parameter is delineated. Moreover, a generic phase diagram indicating tricritical behaviour near and away from the dislocation is depicted. The relation between classical nucleation theory and the Ginzburg–Landau approach is discussed, for which the critical formation energy of the nucleus is related to the maximum of the Landau potential energy. A numerical example illustrating the application of the model to the case of nucleation of hydrides in zirconium alloys is provided. 相似文献
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R.C. Cammarata 《哲学杂志》2013,93(6):927-948
Gibbs formulated a complete and general thermodynamics for surfaces in multicomponent fluid systems. When considering solid–fluid surfaces, he restricted attention to single-component solids in contact with fluids that could contain multiple components. Attempts that have been offered to generalize Gibbs’ results for surfaces between multicomponent solids and fluid are problematic owing to the difficulty that the surface chemical potentials for components that also reside on substitutional lattice sites in the solids are not well defined. Therefore any expressions involving these surface chemical potentials, such as the conventional definition of the surface energy, will also not be well defined. In order to formulate a general thermodynamics of equilibrium that takes into account capillary effects in systems containing surfaces between a multicomponent solids and fluids, it is shown that the concept of thermodynamic availability (exergy) can be employed that, when applied to surfaces, depends on the extensive but not the intensive variables (such as the chemical potentials) of the surfaces. Using this approach, Gibbs–Thomson–Freundlich effects for finite-size solids, an adsorption equation for solid–fluid surfaces and the thermodynamics of nucleation during solidification can be treated in a straightforward manner without referring to the ill-defined surface chemical potentials. A derivation is given that appears to be the first one that properly generalizes Gibbs’ analysis for the reversible work to form a critical nucleus to the case of solidification. 相似文献
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We study metastability and nucleation for the Blume-Capel model: a ferromagnetic nearest neighbor two-dimensional lattice system with spin variables taking values in {–1,0, +1}. We consider large but finite volume, small fixed magnetic fieldh, and chemical potential in the limit of zero temperature; we analyze the first excursion from the metastable –1 configuration to the stable +1 configuration. We compute the asymptotic behavior of the transition time and describe the typical tube of trajectories during the transition. We show that, unexpectedly, the mechanism of transition changes abruptly when the lineh=2 is crossed. 相似文献
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Ralf Blossey 《Annalen der Physik》2001,10(9):733-775
Undercooled wetting films near a first‐order wetting transition exhibit an unusually long lifetime: the thermal nucleation barrier for formation of a critical hole in a film of thickness F diverges according to Γ ∼ exp (ℰc/kBT) where the excess free energy ℰc ∼ Fζ with ζ ≥ 2. Localized perturbations of the liquid‐vapor interface (‘dimples’) are shown to be a useful tool in reducing Γ in a controlled way: they act as heterogeneous nucleation centers for thermal critical nuclei. For 4He wetting films on weak‐binding alkali substrates (Cs, Rb) dimples can be generated either by vortices in a superfluid film or by surface electrons. The theory of the heterogeneous nucleation process initiated by the presence of surface dimples (‘dimple‐assisted dewetting’) is developed, accompanied by quantitative predictions for experiment. 相似文献