合金沉淀过程的微观相场法计算机模拟

讨论了连续体相场动力学与微观相场动力学理论在描述合金相变方面各自的特点.基于微观相场动力学理论建立的微扩散方程,以原子占位几率和序参数描述合金沉淀过程的原子簇聚和有序化.该模型将三维问题进行二维投影,在倒易空间求解,直观给出原子演化图像,并可描述形核、长大、和粗化在内的全过程.微扩散模型已成功用于二元及三元合金沉淀机制及微观组织的模拟.     

二元合金有序化反应研究进展

介绍了两个先进的二元合金有序化反应动力学模型、以及利用计算机对此类合金组织演化模拟取得的进展。先进的模型可成功地描述原子有序化及相分离 ,并将形核、长大和粗化在同一物理模型内加以考虑。利用此模型已对许多重要新型合金的相变动力学进行了模拟研究     

共格颗粒沉淀动力学研究进展

基于经典动力学和失稳分解转变理论，介绍了两个先进的共格颗粒沉淀动力学模型，以及利用计算机对合金共格沉淀过程组织演化模拟取得的进展。该模型可成功地描述共格沉淀相的形貌、反粗化现象、原子有序化、界面的演化等，并将形核、长大和粗化在同一理论框架内考虑。利用该模型已对许多新型具共格畸变合金的相变动力学进行了模拟研究。     

二元合金有序化反应研究进展

介绍了两个先进的二元合金有序化反应动力学模型,以及利用计算机对此类合金组织演化模型取得的进展,先进的模型可成功地描述原子有序化及相分离,将将形核,长大和粗化在同一物理模型内加以考虑,利用此模型已对许多重要新型合金的相变动力学进行了模拟研究。     

聚醚砜-环氧树脂共混体系相分离过程的数值模拟

在热塑性聚醚砜（PES）增韧改性热固性环氧树脂复合材料的制备过程中,通过控制PES-环氧树脂树脂共混体系相分离过程实现共混物相结构的调控,能够明显改善热固性环氧基体树脂的冲击强度。考虑PES-环氧树脂共混体系在相分离过程中PES应力松弛现象以及环氧树脂固化反应现象,采用黏弹性模型描述微观相形态的具体演化路径,揭示了树脂共混体系相分离过程的机制及动力学过程,分析了PES含量、PES分子量大小、PES与环氧树脂的动力学不对称程度以及固化工艺条件等材料及工艺参数对共混体系相结构演变过程以及最终相形态的影响规律及程度,从而为优化PES-环氧树脂树脂共混体系的微观相结构打下基础。     

Ni75Al7.5V17.5合金时效沉淀D022相的孪生相场模拟

为揭示合金固态相变初期新相形成机制,尤其是D022相变孪晶形成机制,利用三元微观相场模型对Ni75Al7.5V17.5合金于1 273 K下等温时效沉淀过程的前3个阶段进行了模拟.计算结果表明,L12结构的Ni3Al有序相首先沿惯析面(100)从母相中共格形核,而后D022结构的Ni3V有序相在先析出的L12相和母相的相界形核.由于{100}的反相畴界上形成较大的共格失配,导致能量较高且不稳定,反相畴界在两相生长中遭到破坏,而晶面{110}的界面能比{100}的反相畴界能低,生长过程中D022的3种变体互相正交排列形成阶梯状结构的{110}孪晶面.     

时效组织演化的计算机模拟理论与模型

总结了时效组织的计算机模拟研究,基于Cahm-Hillard的非经典转变理论,提出一种新的动力学模型,不同于以往的连续介质模型,为离散格点形式,可租用于时效过程的所有阶段,包括形核、长大、粗化等,模型还可描述原子有序化和相分离,并考虑到弹性能对形貌演化和粗化过程的影响,且体积分数的影响、沉淀颗粒间的相互作用也在方程中自动体现。     

Al-Cu合金时效组织演化的数值模拟

介绍了了种基于卡恩－希利 阿德方程（CHE）的动力学模型,该模型给经典CHE中加入影响沉淀相形貌的各向异性弹性应变能,通过CALPHAD方法获得热力学数据以保证模拟真实过程,可用于模拟Al-Cu合金的调幅分解和非匀相时效,后者须假定晶核先存在,因模型不包括成核机制。     

外加应力作用下Ni75Al11.5V13.5合金时效沉淀相的定向粗化

为研究镍基合金Ni75Al11.5V13.5等温时效沉淀颗粒在外应力场作用下的长大,在三元微观相场模型中引入外加应力场,模拟1 046.5 K时效产物L12和D022在外加应力作用下的定向粗化.计算结果表明,微观相场模型可以模拟相结构和晶格中的原子配置,并能清晰地模拟有序相沉淀颗粒间界面.外加应力大小和方向以及持续施加的时间对L12沉淀时效行为有显著影响,施加的外加应力越大、持续时间越长,外加应力方向的定向粗化效应越明显.时效过程中,D022相在L12相与母相界面形核且D022相L12相的间隙中生长,其形态始终受L12相的制约.     

晶体相场模型在异质外延中的应用现状

晶体相场模型作为一种新的模拟技术,较之传统的模拟方法(如分子动力学和标准相场模型)具有突出的优势,能够在原子长度尺寸和扩散时间尺度上模拟材料微观结构的演化过程。晶体相场模型在异质外延中的应用已取得很大进展。简述了纯物质和二元合金晶体相场模型,并且综述了晶体相场模型在异质外延中的研究现状,指明该模型的进一步研究方向及在外延薄膜中的应用。     

Microscopic models of hardness

Recent developments in the field of microscopic hardness models have been reviewed. In these models, the theoretical hardness is described as a function of the bond density and bond strength. The bond strength may be characterized by energy gap, reference potential, electron-holding energy or Gibbs free energy, and different expressions of bond strength may lead to different hardness models. In particular, the hardness model based on the chemical bond theory of complex crystals has been introduced in detail. The examples of the hardness calculations of typical crystals, such as spinel Si₃N₄, stishovite SiO₂, B₁₂O₂, ReB₂, OsB₂, RuB₂, and PtN₂, are presented. These microscopic models of hardness would play an important role in search for new hard materials.     

气体多孔电极反应微观机理及宏观现象的研究

提出多孔电极研究的新思路、新方法，探索电极反应的微观机理及宏观现象，试图为制造高效多孔电极提供理论参考。通过锌空气电池实验对比了立式多孔碳电极相对于传统多孔碳电极在放电中的优点。通过实验观察了三相界面的形成形态随时间变化的3个宏观过程，根据3个宏观过程对应的电化学过程定义了电极反应中所形成的2种有代表性的三相界面。分析了电解液在多孔电极中运动的微观机理并得出理想突变界面是气体电极的最佳工作状态的结论。     

Microscopic aspects of polymer-metal epitaxy

The textured oriented overgrowth (epitaxy) of certain metals evaporated on to substrates consisting of highly oriented ultra-thin thermoplastic polymer films has been known for a few years. However, the origin of the observed epitaxy was not clear: the formation of a chemical interface layer, classic epitaxy or graphoepitaxy (artificial epitaxy) all seemed to be possible explanations for the observed orientations. We have used the complementary methods of transmission electron microscopy (TEM) and scanning force microscopy (SFM) to investigate aspects of the polymer-metal epitaxy. Our investigations show that the bulk morphologies of polymer substrates determine their surface topographic properties. Highly oriented surface steps serve as suitable locations for an oriented growth of the evaporated metals. The results of the investigations suggest artificial epitaxy (graphoepitaxy) as an effective orientation mechanism for the oriented metallic growth on polymer substrates.     

Microscopic imaging with electrogenerated chemiluminescence

The use of electrogenerated chemiluminescence (ECL) at microelectrodes as a light source for scanning optical microscopy is demonstrated. Cone-shaped microelectrodes were constructed by flame etching carbon fibers to a fine point. ECL generated in solution at such electrodes was forced to the apex of the conducting surface by using high-frequency (20-kHz) potential pulses and high concentrations of ECL reagents in the solution. ECL arose from the reaction of 9,10-diphenylanthracene radical cation with the radical anion of benzonitrile, the solvent. The electrode/light source was raster-scanned a finite distance above the sample surface, and images were generated with standard scanning probe software by collecting the transmitted light with a microscope objective. These images compared favorably to optical images of the same sample. A resolution of approximately 600 nm was achieved with this arrangement even though a feedback loop was not employed to control the tip distance from the sample. The source was sufficiently bright (1.82 pW) that well-defined transmittance spectra could be obtained at individual locations on the sample.     

High-Speed Cinematography of Microscopic Organisms

Many cells bear thin, hair-like appendages about 0.2 µm in diameter and between 10 and 500 µm long, called cilia or flagella. For flagella which beat rhythmically in a plane and can be constrained to move within the field of an optical microscope, stroboscopic techniques can be used to observe and analyse the motion. Flagella of many cells execute a threedimensional beat, while other important movements occur spasmodically. Such non-repetitive behaviour is not amenable to stroboscopic observation but requires a technique in which individual images are recorded as a function of time. One such technique is high-speed cinephotography, which has been used to obtain information about the movement of a variety of cells.

To illustrate the effectiveness of the method, we describe a series of experiments in which active flagella were damaged by firing a laser through the microscope from eyepiece to objective in such a way that the laser beam was focused on a local region of the flagellum. High-speed cinephotography was used to record the response of the system to laser damage, and the results are of importance to our understanding of the molecular machinery within the flagellum which is responsible for the externally observed motility.

The use of high-speed cinephotography generates much material for subsequent analysis. To facilitate interpretation of our photographs we have modified a standard back-projection system to provide a semi-automatic, computer-controlled instrument which will track along the image of a flagellum and record the coordinates of the centre-line. If required, preliminary processing of the results can be effected in the computer, which will then present the data in a form suitable for further analysis.     

Microscopic Theory of Organic Superconductors

A microscopic theory of organic superconductors based on the concept of partial electron dielectrization is developed from first principles. Self-consistent equations for the superconducting order parameter () and insulating order parameter (D) are derived using a Green's function technique and equation of motion method. The theory is applied to explain the experimental results in the two-dimensional organic superconductor k-(BEDT-TTF)₂ Cu(NCS)₂. The present model explains coexistence of spin density wave (SDW) state and superconductivity state in the system. The behavior of superconducting order parameter (), insulating order parameter (D), specific heat, density of state, free energy, and critical field is also studied for the system k-(BEDT-TTF)₂ Cu(NCS)₂.     

Microscopic characterization of sol-gel processed cordierite

Different analytical techniques have been used to characterize green and sintered sol-gel processed cordierite on a microscopic scale. The sintered material, although identified macroscopically as -cordierite, contains many small precipitates of different chemical composition. Larger precipitates, characterized by an increased Mg concentration, result from inhomogeneities in the precursor gel. Smaller precipitates, identified as mullite and spinel, could not be related to gel heterogeneities. The amorphous phase surrounding the cordierite grains and the precipitates is Mg depleted and Si enriched. Neither -cordierite nor -cordierite were observed; slight variations of the -cordierite lattice parameters are attributed to some local perturbations due to a slight departure from stoichiometry or Si, Al ordering on tiny domains.     

Microscopic observation of filter cake formation

Particle collisions and filter cake collapse are observed through a microscope during the formation of filter cakes. Cake filtration is widely applied throughout industry for fluid-particle separations. Models and theories have been developed to describe and predict filter cake performance, but there is little literature on direct observation of particle packing and cake formation. A filter assembly the size of a microscope slide is placed on the microscope such that the slurry flow and cake formation is across the field of view. The cake formation is recorded on video tape. Photographs of the video image show particles in the slurry colliding with and sometimes adhering to other particles when forming the filter cake. The photographs also show the cake structure collapse as the cake compacts or compresses.