钛-氢体系的物理化学性质

综合评述了钛一氢体系的物理化学性质。钛是一种具有同素异型转变点L（1155K）的吸氢金属，氢在α钛和β钛中有不同的溶解度，在Tc以下易形成具有面心立方晶格结构的TiH2，氢原子溶解在晶格中，占据四面体间隙位（T）。钛加热吸氢时晶格发生膨胀，产生体胀效应，当温度降低时氢化物又会沿惯习面发生偏析。氢在钛中的扩散在高温时表现为正常扩散即lnD与1／T呈直线关系，在低温时存在隧道扩散。钛一氢体系的热力学p—c-T曲线表现出良好的平台性且在高于593K时存在两个平台。测定了钛一氢体系的反应的动力学扩散活化能和表观活化能。     

钢在氮基保护气氛奥氏体化过程中氢的扩散问题

本文对钢在氮基保护气氛奥氏体化过程中氢的扩散问题进行了研究。结果表明:在保护奥氏体化过程中钢样中氢的化学势比气氛中高而导致钢中的氢向保护气氛中扩散。     

以剩余扩散氢浓度为自变量的扩散氢逸出速率数学模型

采用水银法测定了3种焊条的熔敷金属在一定温度下的氢逸出曲线,由氢逸出曲线计算得到扩散氢逸出速率随剩余扩散氢浓度的变化关系,基于这一关系建立了以剩余扩散氢浓度为自变量的扩散氢逸出速率数学模型vH=k·CαH,该模型能够较好地表征vH与CH的相关性。     

氢在贮氢合金中的扩散

评述了吸氢电极充放电过程中氢在贮氢合金中的扩散行为、氢扩散的研究方法以及扩散系数的影响因素。     

API X52管线钢在饱和硫化氢气田水溶液中的氢渗透与氢致开裂行为

天然气输送管道氢致开裂问题日益突出,而API X52管线钢在气田模拟水溶液中氢渗透和氢致开裂的研究较少。模拟了饱和硫化氢某气田水溶液,采用电化学和恒载荷拉伸试验方法,测定了API X52管线钢在不同充氢电流密度下的氢扩散系数、可扩散氢浓度(ω0)及管线钢氢致开裂临界可扩散氢浓度(ωHIC)。结果表明:API X52管线钢可扩散氢浓度(ω0)与充氢电流密度呈线性关系,即ω0=0.99+0.07J;其恒载荷下开裂临界可扩散氢浓度的对数值(lnωHIC)随拉应力(σ)呈线性下降,即σ=475-450lnωHIC。     

离子微探针研究氢在材料中行为的新进展

本文阐述了我们近年来利用离子微探针对氢在材料中的基本行为研究取得的若干新进展:(1) 在裂纹尖端氢分布研究方面有突破性进展,首次实验发现在受载裂纹尖端存在着氢富集的双峰,对氢双峰的变化规律和形成原因进行了系统研究,并提出了相应的模型;(2) 实验确证了氢在六角密堆结构(hcp)和高位错密度(10~(12)/cm~2)材料塑性形变过程中的可动位错输运行为,并揭示了氢在位错芯部的“隧道扩散效应”;(3) 定量测定了工程厚度材料微区氢浓度分布,通过Fourier变换和Laplace变换,建立了新的微区氢扩散方程解析式,具有重要的实用价值。     

590MPa级高强度焊条扩散氢逸出速率表达式

利用水银法与热提取法试验测定了590 MPa级高强度焊条在不同温度下的扩散氢逸出速率,建立了与温度相关的扩散氢逸出速率表达式,并验证了该表达式的有效性。结果表明,该表达式可以较为准确地计算出焊缝金属冷却过程中的瞬态扩散氢浓度。     

钢焊接接头中氢的溶入与扩散行为研究进展

综述了钢焊接接头中氢的溶入与扩散行为研究进展,介绍了钢焊接接头中氢的来源及氢的溶入模型,测定了氢在部分钢种中的扩散系数,初步确定了氢的扩散和逸出规律及主要影响因素、氢在焊接接头中的分布特征。     

金属氢损伤测试方法分析

介绍了金属中扩散氢含量的测定方法和金属氢损伤的检测方法。在阐明各方法测试原理基础上,重点分析了每种方法的优缺点,以便优选氢损伤的测试方法,建立氢损伤的定量分析技术。     

LZ45CrV车轴钢氢扩散行为及氢鼓泡探究

为了探究LZ45Cr V车轴钢与氢的交互作用,采用Devanathan电化学充氢技术测量了LZ45Cr V车轴钢的氢扩散系数,通过偏振光显微镜观察了氢鼓泡特征,研究了组织结构对氢扩散行为的影响。结果表明:LZ45Cr V车轴钢25°C下的氢扩散系数为1.101×10~(-6)cm~2/s,其细化的金相组织以及较大铁素体中析出的VC粒子,大幅增加了钢中的氢陷阱数量,从而使得LZ45Cr V车轴钢具有较低的氢扩散系数和较高的产生氢鼓泡临界可扩散氢浓度。     

Hydrogen transport and large strain elastoplasticity near a notch in alloy X-750

The finite element method is used to solve the coupled large strain elastoplasticity boundary value problem and transient hydrogen diffusion initial boundary value problem. As an example, solutions are obtained in the neighborhood of a rounded notch in a 4-point bend specimen of alloy X-750 at two temperatures under plane strain deformation conditions. The model accounts for the dilatational strain caused by the presence of hydrogen in the lattice and the hydrostatic stress induced drift of hydrogen. The hydrogen population profiles in both normal interstitial lattice sites (NILS) and trapping sites are calculated and conditions for the predominance of the total amount of hydrogen by either of the populations are studied. The competition between hydrostatic stress and plastic strain in the enhancement of local hydrogen concentrations is investigated. The effect of different types of traps on the relative level of trapped hydrogen as a portion of the total hydrogen is examined. The numerical analysis in conjunction with current experimental evidence suggests a specifically designed line of experiments that will isolate the parameters crucial to hydrogen induced material degradation in X-750.     

Hydrogen trapping phenomena in carbon steel

Hydrogen trapping phenomena in carbon steel with different amounts of trapping sites were investigated by thermal analysis and permeation experiments. In thermal analysis, the relative amount of trapped hydrogen and the activation energy for evolution from various lattice defects were calculated by monitoring the pressure change caused by the release of hydrogen from hydrogen-charged specimens heated at a uniform rate. Hydrogen release peaks were observed at 116, 205 and 387° C, respectively, when the hydrogen-charged specimens with various defects were heated at a constant heating rate of 2.6° C min^–1. Analysis suggested that the peak at 116° C corresponded to release from ferrite-cementite interfaces and the peak at 205° C corresponded to release from dislocations. The activation energy for evolution of trapped hydrogen determined experimentally from the measured peak temperature at different heating rates was found to be 18.4 kJ mol^–1 in the ferrite-cementite interface. The hydrogen energy level around the trapping site was suggested from the trap activation energy and expected saddle-point energy. It was observed that most of the hydrogen is trapped in dislocations in spheroidized 0.49 wt% carbon steel.     

A New Analysis of Hydrogen Diffusion in Metals with Trapping

A new model of hydrogen diffusion in metalshas been developed,it is more efficient todescribe the hydrogen diffusion with trappingin metals.In the model newly developed an impli-cit dependence on time of hydrogen diffusioncoefficient in metals with trapping was firstlybuilt and it is shown that hydrogen diffusioncoefficient will be different at different posi-tions in a dynamic process of hydrogen diffusionin a metal.Numerical solutions of the present modelwere obtained by finite difference method.Bychanging the parameters in the model the diffusionof hydrogen in a metal and the effect of trappingwere described and discussed.And the comparisonbetween the well known McNabb and Foster's modeland the present model was also made.     

Hydrogen diffusivity in FeAl

The room temperature diffusivity of hydrogen in a fully B2 ordered iron aluminide of composition Fe-35·8 Al was estimated from the experimental hydrogen depth profile to be 2·38×10⁻¹⁵m²/s. The mathematical procedure utilized for data analysis has been described. The estimated diffusivity is a lower bound value due to surface trapping effects.     

Visualization of hydrogen diffusion in steels by high sensitivity hydrogen microprint technique

Hydrogen diffusion in steels was examined by both a high sensitivity hydrogen microprint technique (HMT) and an electrochemical hydrogen permeation method. The main diffusion path in an extremely low carbon steel was lattice within grains; grain boundaries were not accelerated diffusion paths. In the case of a hypo-eutectoid steel, hydrogen diffused through proeutectoid ferrite and ferrite in pearlite under steady-state of hydrogen diffusion. The diffusion paths, however, were carbide/ferrite interfaces when hydrogen charging was interrupted before achievement of the steady state. This is probably ascribable to the reversible trapping effect of the interface. The detection efficiency of the high sensitivity HMT was 75% for the low carbon steel and 40% for the hypo-eutectoid steel.     

Hydrogen embrittlement of a bimaterial

Commonly, within the energy industry, the corrosion resistance of pressure vessel steels is increased by the addition of an overlay coating comprising a nickel-based alloy or a stainless steel. However, the interface between the two alloys is prone to hydrogen-assisted cracking, due to for example carbide precipitation near the interface. In the present study, the sensitivity of the tensile strength of the interface to hydrogen concentration is measured for both notched and un-notched specimens made from the overlay welding of 690 nickel alloy on a low alloy steel A533B. An elastic–plastic finite element analysis is used to determine the stress and strain state near the notch root, and thereby to calculate the local distribution of hydrogen within the lattice and at traps. The observed strength of the notched specimens is best rationalised by assuming that the local cohesive strength of the interface is a function of the lattice hydrogen concentration, with a negligible influence of the trapped hydrogen. The scatter in specimen strength, and the relative strength of the notched and un-notched specimens, are adequately described by Weibull statistics, with a low value of Weibull modulus equal to 3.4.     

Visualization of hydrogen diffusion in steels by high sensitivity hydrogen microprint technique

Hydrogen diffusion in steels was examined by both a high sensitivity hydrogen microprint technique (HMT) and an electrochemical hydrogen permeation method. The main diffusion path in an extremely low carbon steel was lattice within grains; grain boundaries were not accelerated diffusion paths. In the case of a hypo-eutectoid steel, hydrogen diffused through proeutectoid ferrite and ferrite in pearlite under steady-state of hydrogen diffusion. The diffusion paths, however, were carbide/ferrite interfaces when hydrogen charging was interrupted before achievement of the steady state. This is probably ascribable to the reversible trapping effect of the interface. The detection efficiency of the high sensitivity HMT was 75% for the low carbon steel and 40% for the hypo-eutectoid steel.     

Hydrogen permeation through a slab sample in the case of high hydrogen concentration

Hydrogen trapping sites have a great influence on the hydrogen permeation through a slab sample. The diffusion of the hydrogen in a crystal is generally governed by a parabolic partial differential equation: a numerical simulation code, realized for the study of the permeation of hydrogen in presence of trapping sites, has been utilized for the analysis of the influence of reversible and irreversible traps on the diffusion of hydrogen in a metal for the case of high (not negligible) hydrogen concentration with boundary conditions which cannot be treated analytically.     

Hydrogen trapping and repelling in an Al-6 wt % Zn-2 wt % Mg alloy

Hydrogen trapping in an Al-6 wt % Zn-2 wt % Mg alloy aged up to typical stages in the agehardening curve has been studied by measuring the tritium release rate after charging. The distribution of hydrogen in the aged alloy has been studied by tritium electron microautoradiography. It has been found that the Guinier-Preston zones in the alloy do not act as trapping sites but as a repeller for hydrogen, and that precipitate does not trap hydrogen, but the interface between the matrix and precipitate acts as a trapping site for hydrogen. Dislocation has been found to be capable of trapping hydrogen, while trapped hydrogen by the grain boundary has not been observed.     

Control of hydrogen cracking in the welded steel using microstructural traps

Hydrogen diffusion into steel can embrittle the material in H₂S environments, but this effect can be offset by suitable hydrogen trapping sites in the microstructure. Fine Ti(C,N) inclusions have been studied as the trapping sites in high strength low alloy (API X-70) welds, with Ti additions ranging from 0.004 to 0.16?wt.%. The trapping sites were investigated by electron microscopy and thermal desorption spectroscopy. Manganese sulphide particles were the main initiation sites for hydrogen induced cracking as expected. The optimum Ti addition was around 0.02% with no evidence of cracking in the weld. The estimated values of trapping activation energy for dislocations, microvoids, MnS and Ti(C, N) were approximately 25.9, 34.6, 65.1 and 87.6?kJ?mol^?1, respectively.