A NEWLY DISCOVERED DIFFUSION MECHANISM IN SOLIDS──COMPLEX DIFFUSION MECHANISM

置换溶质原产可以以溶质原子－空位复合体形式扩散，这一扩散机制可以圆满的说明非平衡偏聚现象发生的规律，密排晶体中溶质原子的异常快速扩散现象，Ｂ在γ－Ｆｅ中快速扩散和晶界非平衡偏聚，溶质原子在Ａｌ表面空位坑中的聚集以及Ｓｉ在Ａｌ晶界处析出等问题．     

固体中一种新发现的扩散机制──复合体扩散机制SCIEI

置换溶质原产可以以溶质原子－空位复合体形式扩散，这一扩散机制可以圆满的说明非平衡偏聚现象发生的规律，密排晶体中溶质原子的异常快速扩散现象，Ｂ在γ－Ｆｅ中快速扩散和晶界非平衡偏聚，溶质原子在Ａｌ表面空位坑中的聚集以及Ｓｉ在Ａｌ晶界处析出等问题．     

固体中一种新发现的扩散机制—复合体扩散机制SCIEI

置换溶质原子可以以溶质原子-空位复合体形式扩散,这一扩散机制可以圆满的说明非平衡偏聚现象发生的规律,密排晶体中溶质原子的异常快速扩散现象,B在γ-Fe中快速扩散和晶界非平衡偏聚,溶质原子在Al表面空位坑中的聚集以及Si在Al晶界处析出等问题。     

离子钨钼共渗的扩散机制

对双层辉光离子钨钼共渗在离子条件下形成的渗层和无离子形成的渗层进行了对比,计算了溶质原子钨和钙与空位的结合能。据溶质－空位复合体扩散的能量条件,提出溶质－空位复合体扩散机制在双层辉光离子钨钼共渗中起重要作用。由此解释了双了离子钨钼共渗的Ｗ和ＭＯ原子快速现象和渗后冷却中大量金属合物在晶界的析出。     

MECHANISM OF NON-EQUILIBRIUM SEGREGATION OF SOLUTE TO GRAIN BOUNDARIES

本文以空位-溶质原子拖曳机制为基础,并考虑了空位、溶质原子和复合体三者的反应平衡及晶界平衡偏聚的作用,得到了溶质原子的非平衡晶界偏聚动力学方程。对硼在奥氏体中等温及连续冷却时所产生的非平衡晶界偏聚现象进行了理论计算,得到了与实验较为一致的结果。     

金属合金等温相变的体激活能及相变机制II.β黄铜等温相变

与钢相似,β黄铜等温处理获得的片状α1(贝氏体)和棒状α都具有自己的C曲线;各转变初期均能获单一相,而转变中、后期通常可获相邻两相的复合体.必须用单一相和Arrhenius关系求相变产物的体激活能.用体激活能,相的形貌和体自由能变化相结合能可诠释下述论点:片状α1(贝氏体)是溶质原子扩散控制下母相β'中的贫溶质区,进行"军队型"原子无扩散马氏体样切变相变;棒状α是溶质原子扩散控制下母相β'中的最贫溶质区,发生"平民型"原子无扩散界面控制相变.     

金属合金等温相变的体激活能及相变机制——Ⅱ．β黄铜等温相变

与钢相似,β黄铜等温处理获得的片状α1（贝氏体）和棒状α都具有自已的C曲线;各转变初期均能获单一相,而转变中、后期通常可获相邻两相的复合体．必须用单一相和Arrhenius关系求相变产物的体激活能．用体激活能、相的形貌和体自由能变化相结合能可诠释下述论点：片状α1（贝氏体）是溶质原子扩散控制下母相β’中的贫溶质区,进行“军队型”原子无扩散马氏体样切变相变;棒状α是溶质原子扩散控制下母相β’中的最贫溶质区,发生“平民型”原子无扩散界面控制相变．     

OVERALL ACTIVATION ENERGY OF ISOTHERMAL TRANSFORMATION IN METAL ALLOY AND ITS MECHANISM II. Isothermal Transformation in β Brasses

与钢相似, β黄铜等温处理获得的片状α₁(贝氏体)和棒状α都具有自己的C曲线; 各转变初期均能获单一相, 而转变中、后期通常可获相邻两相的复合体. 必须用单一相和Arrhenius关系求相变产物的体激活能. 用体激活能、相的形貌和体自由能变化相结合能可诠释下述论点: 片状α₁(贝氏体) 是溶质原子扩散控制下母相β' 中的贫溶质区, 进行“军队型”原子无扩散马氏体样切变相变; 棒状α是溶质原子扩散控制下母相β' 中的最贫溶质区, 发生“平民型”原子无扩散界面控制相变.     

Ni3Al中B和Mg的非平衡晶界共偏聚

在1023－1373K的初始温度和0.05-268.91K/s的冷速范围内，用Auger剖层分析确定含B和Mg的Ni3Al合金中B和Mg的非平衡晶界共偏聚行为，按照溶质－空位复合体迁移机制所导出的描述非平衡晶界偏聚的扩散速率方程解析表达式，很好地模拟了本实验结果，并确定了Ni3Al-B-Mg合金中B及B－空位复合体，Mg及Mg-空位复合体的扩散系数及复合体激活能。     

扩散过程中空位的作用及其地位

本文讨论了空位对间隙原子和代位式原子扩散的影响及它们之间的相互作用:在间隙合金中,由于复合体的存在,间隙原子与空位在扩散过程中将通过复合体的形成与分解反应而相互关联;在|E_b|相似文献   

Effects of atomic mobilities on phase separation kinetics: a Monte-Carlo study

An atomistic kinetic model with a vacancy-mediated diffusion mechanism is used to study the precipitation kinetics from a supersaturated solid solution. For a given alloy thermodynamics, varying the asymmetry of the pairwise interaction energies determines the vacancy–solute binding energy and modifies the ratio of the solute to solvent mobility. We show that this asymmetry determines the weight of the coagulation process relative to the evaporation–condensation mechanism, and the location of the dynamical percolation limit. We also observe that when temperature is decreased, KJMA exponents increases, in agreement with experimental observations, but at variance with kinetic simulations carried out with the standard direct atom exchange dynamics.     

快速凝固中局部非平衡溶质截留的分析模型(英文)

对二元合金快速凝固过程中的局部非平衡扩散模型(LNDM)进行改进。改进的模型考虑了熔体中溶质浓度和溶质通量流场与局部平衡的偏差。采用双曲函数扩散方程求得了熔体中溶质浓度和通量的准确解。结果表明,对任何固?液界面的动力学,当有效扩散系数DbLNDM→0和在v→vDb发生完全溶质截留KLNDM(v)→1时,凝固过程将由扩散控制转变为完全的热控制。非扩散凝固和完全溶质截留的临界参数为在溶体中的扩散速度vDb,考察了不同界面动力学途径的溶质截留模型。     

直流磁场对7075铝合金组织结构的影响

研究了在直流磁场下凝固的7075铝合金晶内溶质含量及凝固组织的变化。试验结果表明：与未施加磁场的试样相比，经过直流磁场处理后，7075铝合金中Zn、Mg、Cu3种溶质元素在晶粒内部的含量均增加。此外，直流磁场作用下，试样宏观组织的变化不明显，而晶内析出相的形貌和尺寸发生了显著变化，由无磁场时的粗大针状组织变为细小均匀的结构。探讨了磁场的作用机制。认为电磁场作用使得各溶质粒子对基体铝产生了相对运动，这种运动增强了溶质粒子在铝中的扩散，从而导致了晶内溶质含量的增加。     

Influence of solute segregation and drag on properties of migrating interfaces

Recent models on solute segregation and drag search for steady-state solutions of the diffusion equation in the region of a migrating interface and adjacent semi-infinite grains. Such solutions are limited to model massive transformations, for which the chemical composition of the parent grains and that of the product grains are the same. Simulation of diffusive transformations in transient systems with grains of different chemical composition is a hot issue. In the present model the steady-state solution of the diffusion equation is investigated only in the interface. The coupling with the diffusion equation in the adjacent grains is ensured by proper boundary conditions. For simulation of transient diffusive phase transformations it is very convenient if the interface can be treated as a sharp interface with a known effective mobility and prescribed boundary conditions at the interface. In this paper it is shown that solute segregation and drag can be taken into consideration by the effective mobility of a sharp interface and by proper boundary conditions at the sharp interface. The effective interface mobility reflects Gibbs energy dissipation due to rearrangement of solvent atoms and to trans-interface diffusion and drag of solute atoms in the migrating interface. Trans-interface diffusion and drag of solute atoms are also reflected by the jump of the chemical potential of the solute across the interface, which represents a boundary condition for coupling with the diffusion equation in the adjacent grains. Finally, it is shown that the incorporation of the effects of trans-interface diffusion and drag of solute atoms does not make the simulation more complicated provided that some necessary calculations are performed in preprocessing.     

Elastic wavefield interactions with solute species during precipitation processes in solids

The linear coupling of elastic deformations and solute diffusion in solids produces effects such as strain-induced diffusion and solute-induced dilatation. Beyond linear theory, there are significant physical effects that must be described using the nonlinear coupling of solute concentration to elastic stiffness. This coupling is developed using a continuum, thermodynamic approach that considers the possible effects that might arise in elastic solids containing a mobile solute species. The related effects of solute concentration on elastic wavespeeds during precipitation processes are modeled and are compared to previously reported experimental results obtained in an aluminum alloy.     

关于贝氏体形核和台阶机制的讨论--与徐祖耀院士等商榷

一些合金固溶化(或淬水)后在预贝氏体(孕育)期内等温淬火(或时效)，既保持高温时形成的晶体缺陷，又产生新的晶体缺陷。母相中由于溶质原子扩散而在缺陷处发生偏聚，则形成贫／富溶质微区，即类拐点(spinoclal—like)分解。当贫溶质微区成分作为Ms，其温度等于或高于等温淬火(或时效)温度时，贝氏体将以马氏体样切变形核，故贝氏体是在溶质原子扩散控制下切变形核。在TEM温台试验中未发现台阶生长机制，界面上巨型台阶是贝氏体增宽(厚)速度差异所致。     

初生硅在熔体中的溶解动力学

研究了初生硅在熔体中的溶解特性，并以原子扩散为模型，考虑界面反应等因素的影响，建立了初生硅在过热熔体中的溶解动力学模型。同时以Al-17%Si合金为研究对象，采用等温液淬技术，对所建立的模型进行了实验验证。结果表明，初生硅在熔体中的溶解机制不是单纯受扩散控制的，而是由扩散、界面反应共同作用的结果，文中所建立的初生硅溶解模型可以较好地描述初生硅在不同温度过热熔体中的溶解特性。     

Mechanism of internal oxidation in silver alloys

The internal oxidation mechanism in silver alloys was studied by residual resistivity, gravimetric, and calorimetric measurements, and by transmission electron microscopy. If the flux, of oxygen atoms is very large with respect to the oxide formation, the mechanism of internal oxidation includes two stages. The first one is the fixation of oxygen in the form of oxidized elementary species, including only one solute atom. These species are stable and keep a certain mobility. The second one is the coalescence process of these elementary species with the formation of the first clusters. When the flux of oxygen atoms is slowed down, the oxide formation mechanisms are more complicated. The initially formed species can include more than one solute atom because of their diffusion. The two stages are not separate.     

基于有限体积法的Al-Cu合金中Cu枝晶生长过程模拟

考虑成分过冷、曲率过冷、界面能各向异性等因素,将有限体积法与元胞自动机相结合,对枝晶生长过程进行模拟,改进了界面推进和溶质扩散过程的计算.结果发现,过冷度、溶质浓度等因素对于枝晶的形貌和生长速度有着重要影响,而在合金的各种物性参数中,液相溶质扩散系数对于枝晶的生长影响尤为显著.