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。     

在Ni3Al中硼的非平衡晶界偏聚

在１０２３～１３７３Ｋ的初始温度范围和０．０５～２６８．９１Ｋ／ｓ的冷速范围内，用俄歇剖层分析确定了含硼Ｎｉ３Ａｌ合金中硼的非平衡晶界偏聚行为。基于由空位在晶界湮灭所产生的体系自由能下降驱动可动的溶质－空位复合体向晶界迁移。从而产生溶质非平衡晶界偏聚的模型，导出了定量描述非平衡偏聚行为的解析表达式，理论计算结果与硼非平衡偏聚的试验数据相符，通过模拟实测确定Ｎｉ３Ａｌ－Ｂ合金中硼及硼－空位复合体的扩     

硼在金属间化合物Ni3Al晶界的平衡偏聚

应用扫描俄歇探针研究了硼在金属间化合物Ｎｉ３Ａｌ晶界的平衡偏聚特性。研究结果表明，硼在Ｎｉ３Ａｌ晶界的偏聚符合Ｌａｎｇｒｎｕｉｒ一ＭｃＬｅａｎ平衡偏聚理论；实验得到硼在Ｎｉ－２４ａｔ．－％Ａｌ合金中晶界偏聚自由能△Ｇ＝－２２１５９－２４．７４Ｔ（Ｊ／ｍｏｌ）：硼在Ｎｉ３Ａｌ晶界的偏聚受晶界结构和晶界化学环境的影响。不同结构的晶界存在着硼偏聚的不均匀性，硼在富镍晶界的偏聚比在富Ａｌ晶界更为显著，合金元素对硼在Ｎｉ３Ａｌ晶界偏聚的影响与其在Ｎｉ３Ａｌ中占据的亚阵位置有关。     

在Ni_3Al中硼的非平衡晶界偏聚

在１０２３～１３７３Ｋ的初始温度范围和０．０５～２６８．９１Ｋ／ｓ的冷速范围内，用俄歇剖层分析确定了含硼Ｎｉ_３Ａｌ合金中硼的非平衡晶界偏聚行为。基于由空位在晶界湮灭所产生的体系自由能下降驱动可动的溶质－空位复合体向晶界迁移、从而产生溶质非平衡晶界偏聚的模型，导出了定量描述非平衡偏聚行为的解析表达式。理论计算结果与硼非平衡偏聚的试验数据相符。通过模拟实测确定Ｎｉ_３Ａｌ－Ｂ合金中硼及硼－空位复合体的扩散系数分别为：Ｄ＝１×１０￣（－６）ｅｘｐ［－１．９６（ｅＶ）／ｋＴ］和Ｄ_（Ｐ（Ｂ））＝１×１０￣（－）４ｅｘｐ［－１．９６（ｅＶ）／ｋＴ］（ｍ￣２／ｓ）；硼－空位复合体的结合能为Ｅ_（ｂ（Ｂ）＝０．５ｅＶ。     

硼在体心立方Fe—3%Si合金中的晶界偏聚行为

利用硼径迹显微照相(PTA)技术研究了体心立方Fe—3%Si合金试样在冷却和淬火等温过程中硼向晶界的偏聚行为结果表明:Fe-3%Si合金中硼的晶界平衡偏聚趋势高于奥氏体合金,也不存在淬火诱导硼向晶界的非平衡偏聚.硼原子与晶界结合能Q=55.7 kJ/mol用淬火诱导非平衡偏聚的复合体机制解释了硼在Fe-3%Si合金与奥氏体合金中偏聚行为异同的原因.     

硼向奥氏体晶界的非平衡偏聚

采用高分辨率的径迹显微照相技术,研究了淬火硼钢中硼向奥氏体晶界偏聚的规律,定量地测定出跨过奥氏体晶界的硼的成分剖面图以及非平衡晶界偏聚的特征参量(晶界贫硼区宽度、晶界富集程度和富集带宽度)。试验表明,这种偏聚具有如下特征: 在偏聚晶界的两侧存在有一定宽度的贫硼区,晶界偏聚的硼是在冷却过程中由该区富集而来;这种偏聚对冷却速度很敏感,急速冷却可以抑制这种偏聚。冷却速度降低,晶界偏聚由连续的偏聚带,逐步发展为不连续的聚集直至明显地析出硼相,贫硼区宽度与冷却速度的平方根成反比;它的温度关系与晶界平衡偏聚预言相反,随淬火温度升高,晶界偏聚程度与贫硼区宽度增加。通过试验,论证了淬火钢中硼向奥氏体晶界的偏聚,是在冷却过程中发生的一种非平衡的晶界偏聚现象。     

硼向奥氏体晶界非平衡偏聚的机制

业已证实,淬火硼钢中硼向奥氏体晶界的偏聚,是在冷却过程中发生的一种非平衡的晶界偏聚。本文通过解变温扩散方程,导出了非平衡晶界偏聚的理论公式,建立了晶界贫硼区宽度与淬火加热温度、冷却速度以及非平衡晶界偏聚扩散激活能与扩散常数之间的关系,理论预言与实验结果较好地吻合。根据实验结果和理论分析,提出这种非平衡晶界偏聚的机制,是在冷却过程中,过饱和空位或双空位带着硼原子向晶界(空位阱)迁移的结果。基于这种非平衡晶界偏聚的新概念,可以较完满地说明影响硼钢淬透性的众多复杂因素。     

微量溶质元素在金属晶界的偏聚

溶质元素在金属晶界的偏聚可以分为两类，即平衡偏聚和非平衡偏聚。本文回顾了这两类偏聚现象及其机理，着重讨论分析了有重要工程用途的三类典型的晶界偏聚：硼在奥氏体晶界的两类偏聚的实验规律及对硼钢淬透性影响；磷在奥氏体晶界的平衡偏聚及对钢回火脆性的作用，钢中的其他合金元素对磷的偏聚的影响；硼在多种金属间化合物的偏聚及对这些金属间化合物塑性的影响及其机理。     

硼在奥氏体晶界的两类偏聚

用PTA法研究了Fe-30％Nj合金中硼在晶界的偏聚行为.实验表明,在550—1200℃保温后,用不同方式冷却的试样中存在有平衡与非平衡两类硼偏聚,其形成机制各不相同,而且试验条件的影响亦不同.保温时形成的平衡偏聚在低温淬火试样中起主要作用.在高温加热后,用通常冷速冷却时,晶界偏聚主要来源于冷却过程中产生的非平衡偏聚.实际试样中观察到的硼偏聚是这两类偏聚的叠加,主要偏聚方式的转折温度区受冷却速度影响,在中等冷速下,这个转折温度在650—750℃之间。     

晶界非平衡偏聚的发生与发展过程

采用硼（Ｂ）径迹照相法和透射电镜从实验上观察了连续冷却过程中Ｂ在晶界非平衡偏聚的发生发展过程。测定了晶界偏聚的富集因子、富集带宽度、贫Ｂ区宽度和贫化因子等偏聚特征参量 实验结果表明，对于Ｂ含量（质量分数）为１０×１０－４％的 Ｆｅ－４０％Ｎｉ合金体系，以 ２℃／ｓ的冷速从 １１５０ ℃冷却到 ６４０℃的时候，Ｂ在晶界上的偏聚经历了 ３段式的发展．并在８６０ ℃时开始向非平衡析出转化。 可以用晶界及晶界附近扩展畸变区对于溶质原子的吸附作用解释上述现象     

Calculation of Selective Oxidation in Grain and Grain Boundary

The aim of this paper is to identify selective oxidation of high strength steels under different conditions. FISHER model is introduced to simulate diffusion and precipitation of chemical elements in metallic matrices and grain boundary, a scheme of its analytical solution is given. Effects of grain size, dew point and annealing temperature related to concentration of oxygen during annealing treatment are presented. The results are consistent well with literatures. The calculation shows that the selective oxidation of CMnSi TRIP steel at ferritic annealing in a low dew point N₂-10%H₂ atmosphere of ?30 °C result in the formation of internal MnO in the matrix and SiO₂ particles in the subsurface. The calculations agree well with the experimental results.     

Computation of Five-Dimensional Grain Boundary Energy

A broken-bond type computational method has been developed for the calculation of the five-dimensional grain boundary energy. The model allows quick quantification of the unrelaxed five-dimensionally specified grain boundary energy in arbitrary orientations. It has been validated on some face-centred cubic metals. The stereo projections of grain boundary energy of ∑3,∑5,∑7,∑9,∑11,∑17 b and ∑31a have been studied. The results of Ni closely resemble experimentally determined grain boundary energy distribution figures, suggesting that the overall anisotropy of grain boundary energy can be reasonably approximated by the present simple model. Owing to the overlooking of relaxation matter, the absolute values of energy calculated in present model are found to be higher than molecular dynamic-based results by a consistent magnitude, which is 1 J/m2 for Ni. The coverage of present method forms a bridge between atomistic and meso-scale simulations regarding polycrystalline microstructure.     

纯钨高压扭转晶界演化和非平衡晶界形成机理

本研究在550℃下对纯钨分别进行了1、2、5和10圈的高压扭转变形,并对变形前后的微观组织进行了EBSD和TEM表征。结果显示,纯钨经过大塑性变形后,晶粒得到细化,大角度晶界比例上升,同时晶内位错逐渐向晶界处移动并产生有序化排列。采用修正位错模型对变形前后的晶界能量进行了计算,计算结果表明纯钨在经过大塑性变形后,晶界上的能量升高并且能量主要来自于变形过程中在晶界处积累的额外位错。同时在变形后的试样中观察到了一种特殊的非平衡晶界,分析可知非平衡晶界的形成条件是材料晶粒尺寸在位错平均自由程以下,并且是在大塑性变形材料中形成的。其在TEM高分辨下的形貌特征表现为较宽的晶界厚度和晶面干涉形成的莫尔条纹。     

复杂金属晶界的准确提取技术

在晶粒度定量评定时,对复杂晶界处理效果差.为解决这一问题,对复杂金属晶界的准确提取技术进行了研究.对金属晶粒度评级的步骤进行分析可知,晶界的准确重建是得到准确定量结果的关键,为此需要解决晶界间断不连续的问题.设计了两种晶界断点连接方法,对比表明,形态学分水岭阈值分割方法的效果更好,但需要解决过度分割和未分割的问题.据此,提出了复杂晶界的准确提取方法,即对区域极小值点进行有效编辑,或在应用watershed变换前在灰度图像上将断点进行连接.     

Grain Boundary Diffusion of Nickel into Copper

A high resolution autoradiographic study of the diffusion of a nickel isotope (Ni⁶³) into copper in the temperature range of 650° to 925°C, with particular emphasis on grain boundary diffusion, has been made. The extent of grain boundary diffusion is a function of the grain boundary angle and the diffusion temperature. The ratios of the grain boundary diffusion coefficient to the lattice diffusion coefficient ranges from 10⁴ to 10⁵. The activation energy for grain boundary diffusion decreases with increasing grain boundary angle.     

氮化硅陶瓷的玻璃相及其晶粒异常长大

利用透射电镜(TEM)研究无压烧结Si3N4-MgO-CeO2系陶瓷的显微结构。发现并用微观衍射分析证实了晶界处有玻璃相出现。透射电镜能谱分析得出,当没有MgO时CeO2的主要功能便是形成玻璃相。硅酸铈玻璃相的出现有利于Si3N4液相的产生。MgO-CeO2是Si3N4陶瓷优秀的烧结助剂。当在1850℃以上温度烧结是会出现Si3N4陶瓷晶粒的异常长大,这将导致裂纹和位错并最终影响其机械性能。     

Ni-Cr-W系高温合金晶界特征分布的研究

通过扫描电子显微镜(SEM)、电子背散射衍射(EBSD)、取向成像显微技术(OIM)研究了在不同冷轧及退火工艺下 Ni-Cr-W 系高温合金晶界特征分布的规律。结果表明,70%变形量下再结晶完成所需时间较短,特殊晶界比例随着退火时间延长先增加后减少;10%变形量下再结晶驱动力较小,再结晶所需时间较长,特殊晶界比例在长时间退火后达到最大值。在晶粒团簇内部,晶粒之间有Σ3n的取向关系,而不同的晶粒团簇间,晶粒则没有这种特殊的取向关系。     

Uniaxial Strain-Induced Grain Boundary Migration in Titanium

The mechanical response of a bi-crystal model with a 90° grain boundary under external compressive and tensile loading parallel to the boundary plane normal was investigated with molecular dynamics simulations.The grain boundary was found to migrate along two opposite directions upon compressive and tensile straining,with the formation of inter-connected coherent twin boundary and basal/prismatic boundary.The atomic details of such grain boundary migration were unraveled,which indicated the role of interface dislocations.The temperature effect was also discussed.     

金属材料晶界工程研究进展

利用晶界工程技术能够显著提高金属材料的力学、化学及磁学性能,因此,晶界工程已成为金属材料研究的一个重要领域。本文对晶界工程的基本理论进行了介绍,在此基础上综述了近年来这一研究领域的发展概况,并提出了未来的进一步研究方向。     

Quantification of Microstructural Evolution in Grain Boundary Networks

In this work, the effect of grain boundary engineering (GBE) on the structure and connectivity of networks of two types of boundaries was quantified. General high angle boundaries and “special” Σ = 3 and Σ = 9 coincident site lattice boundaries were considered. The effect of GBE processing was to increase the population and length of special boundaries and to disrupt the network of high-angle grain boundaries (HAGBs) in the microstructure. The GBE processing resulted in an increase in the population of special boundaries as determined by line length fraction from approximately 37% to approximately 57%. The connectivity of the special boundaries, as determined by topological analysis, increased by a factor of 4, while the connectivity of HAGBs decreased by an order of magnitude. Cluster sizes in the special boundary network increased across the range of sizes, and the maximum cluster size of HAGBs decreased significantly. The metrics reported here allow for a quantitative analysis of grain boundary connectivity in microstructures, as well as for a quantitative means of comparison of microstructures. These metrics will be used in simulations of diffusional creep, with the aim of quantifying structure–property relationships in grain boundary engineered systems.