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。     

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。     

Ni-Cr钢中P的非平衡晶界偏聚现象

采用Auger电子能谱仪分析了经过1000℃淬火后600℃时效过程的Ni-Cr钢中元素磷的晶界偏聚浓度,得到晶界P的偏聚浓度随时效时间变化的动力学曲线。结果表明,Ni-Cr钢在600℃时效60 min时,P的晶界偏聚浓度出现极大峰值,与平衡晶界偏聚模型不符。利用溶质的非平衡晶界偏聚模型进行分析,证实这是由于钢中P的非平衡偏聚临界时间现象引起的。     

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     

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     

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。     

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。     

THE MECHANISM OF NON-EQUILIBRIUM SEGREGATION OF BORON TO AUSTENITE GRAIN BOUNDARIES

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。     

磷元素的非平衡晶界偏聚对A690M海洋环境用钢耐海水腐蚀性能的影响

采用俄歇能谱分析了A690M海洋环境用钢在600℃回火过程中磷元素的晶界偏聚行为,结合极化曲线和腐蚀锈层的微观分析探讨了P元素晶界偏聚对A690M钢耐海水腐蚀性能的影响。研究表明:A690M钢中P元素的晶界偏聚符合空位-溶质原子复合扩散导致的非平衡偏聚机制;P的晶界偏聚含量越高,锈层内部越易形成层状磷疤坑,使板坯耐海水腐蚀性能降低。     

TEM+EDX技术分析铈和磷在α-Fe晶界的偏聚

提出了用TEM+EDX技术分析溶质在晶界的偏聚所必需的近似处理方法。用该技术分析了Fe-0.3％P-0.16％Ce合金中铈和磷的晶界偏聚,并将结果与AES在同一合金中的结果进行比较。结果表明,TEM+EDX结合所提出的近似处理方法研究溶质的晶界偏聚现象是可行的。在Fe-0.3％P-0.16％Ce合金中测得铈和磷在晶界上有较高浓度的共偏聚。本文还研究了铈在α-Fe晶界平衡偏聚的规律。     

PHASE INTERFACE SEGREGATION OF Mg IN A Ni-BASE SUPERALLOY IN100

The segregation of Mg to phase interfaces in a nickel base superalloy IN 100 has been investi-gated using EPT(Electron Microprobe Technique).AES(Auger Electron Spectroscopy)and EDS analyses on thin TEM film.The results show that Mg segregates to the phase inter-faces of MC/γ and γ′/γ.The segregation concentration and layer thickness of Mg onMC/γ phase interface are larger than that on γ′/γ phase interface.Mg is not only a grainboundary segregation element,but also a phase interface segregation one.     

夹杂物对铜在钢氧化过程中富集行为的影响

对于含有0.3%残余元素铜的中碳钢,在1100℃下氧化1800s和3600s,利用扫描电镜和能谱仪观察氧化层与钢基体界面处铜的富集析出情况。并分析S、Ti等元素含量对于残余元素铜在氧化层附近富集情况的影响。结果表明,钢中硫化锰夹杂物数量的增多有利于更多的铜在硫化锰上析出,从而有效减轻铜在钢氧化层的富集偏析以及浸润晶界现象。     

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.     

稀土对钢轨钢界面杂质偏聚的抑制作用

利用俄歇能谱(AES)分析技术,对钢轨钢的界面(解理面、晶界面)进行成分分析。实验结果表明,钢轨钢中加入稀土元素后,界面上的P、S原子偏聚基本消失,使界面得到明显的净化。     

THE NON-EQUILIBRIUM SEGREGATION OF BORON TO AUSTENITE GRAIN BOUNDARIES

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。     

Effects of low-frequency magnetic field on grain boundary segregation in horizontal direct chill casting of 2024 aluminum alloy

1. Introduction Grain boundary segregation in alloys is a scientifically interesting and technologically important subject. Serious grain boundary segregation in direct chill casting of aluminum alloy leads to a great reduction in strength and toughness after heat treatment and mechanical deforma- tion [1,2]. In order to reduce grain boundary segregation, rapid solidification methods are often adopted[3]. However, rapid solidification methods require elaborate processing and/or special expensi…     

Phosphor in Eisen und Stahl – Ein Überblick über grenzflächenanalytische Untersuchungen am Max-Planck-Institut für Eisenforschung zum Segregationsverhalten des Phosphors an äußeren und inneren Grenzflächen von Eisen und Stahl

Phosphorus in iron and steel – An overview of surface analytical investigations of the segregation behaviour of phosphorus on internal and external iron and steel surfaces The surface segregation of phosphorus was studied on (100) oriented single crystals of the type Fe? P and Fe? Si-P. Phosphorus shows a strong tendency to enrich at surfaces. The interaction with lattice defects leads to an additional enrichment below the surface. A strong repulsive interaction of phosphorus with segregating silicon can lead to a complete displacement of silicon from the surface region. Equilibrium segregation experiments revealed a segregation enthalpy for phosphorus of ?180 kJ/mol for the ternary system Fe? Si? P, this is only slightly lower than the segregation enthalpy of the extremely surface active sulfur in iron anti steel. The strong tendency of phosphorus to enrich at interface in iron and steel is also observed for grain boundaries. The grain boundary segregation of phosphorus was studied for the systems Fe? P, FeC? P, Fe? M? P and Fe? M? C? P with M ? Cr, Mo, V, Ti, Nb. The segregation of carbon leads to the displacement of phosphorus. By the presence of carbide forming elements like chromium in the material this positive effect is reduced. Elements, that can tie up phosphorus, like titanium and intermetallic phases, that dissolve phosphorus, -an also reduce the segregation of phosphorus. addition ally a phosphorus segregation to the interface carbide/matrix was observed.     

The role of magnesium segregation in the intergranular stress corrosion cracking of aluminium alloys

Stress corrosion susceptibility of aluminium alloys has been related to the grain boundary segregation of magnesium. In this paper segregation mechanisms are reviewed and examined with reference to both direct and indirect experimental evidence for magnesium segregation. Important parameters considered are the solution heat treatment temperature and the effect of grain boundary precipitation. Evidence to support both equilibrium and non-equilibrium segregation of magnesium is presented. Significantly magnesium segregation promotes hydrogen entry into aluminium but in isolation is not responsible for cracking susceptibility which depends on a critical grain boundary precipitate/hydrogen interaction.     

合金元素在fcc-Fe/NbX(X=C,N)界面的偏析及影响

基于密度泛函理论(DFT)第一性原理方法,研究了Si、Ni、Mn、Cr、Mo在fcc-Fe/NbX (X=C, N)界面的偏析行为,并分析了合金元素偏析对界面体系的影响。结果表明,fcc-Fe/NbN界面结合强度相较于fcc-Fe/NbC界面结合强度略有提升;Si稳定存在于Fe基体中,Ni、Mn在界面有轻微偏析倾向,Cr、Mo在界面和NbX (X=C,N)内均存在偏析,其中,Mo向界面偏析倾向更大;Cr、Mo偏析在fcc-Fe/NbC界面一定程度上降低了界面的结合能力,但体系稳定性有所提升,Cr、Mo偏析在fcc-Fe/NbN界面一定程度上提高了界面的结合能力,但Mo使得体系稳定性下降。