The electrochemical permeation test is one of the most used methods for characterising hydrogen diffusion in metals. The flux of hydrogen atoms registered in the oxidation cell might be fitted to obtain apparent diffusivities. The magnitude of this coefficient has a decisive influence on the kinetics of fracture or fatigue phenomena assisted by hydrogen and depends largely on hydrogen retention in microstructural traps. In order to improve the numerical fitting of diffusion coefficients, a permeation test has been reproduced using FEM simulations considering two approaches: a continuum 1D model in which the trap density, binding energy and the input lattice concentrations are critical variables and a polycrystalline model where trapping at grain boundaries is simulated explicitly including a segregation factor and a diffusion coefficient different from that of the interior of the grain. Results show that the continuum model captures trapping delay, but it should be modified to model the trapping influence on the steady state flux. Permeation behaviour might be classified according to different regimes depending on deviation from Fickian diffusion. Polycrystalline synthetic permeation shows a strong influence of segregation on output flux magnitude. This approach is able to simulate also the short-circuit diffusion phenomenon. The comparison between different grain sizes and grain boundary thicknesses by means of the fitted apparent diffusivity shows the relationships between the registered flux and the characteristic parameters of traps.

中文翻译：

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考虑铁中晶界俘获的两种不同建模方法的氢渗透测试分析

电化学渗透测试是表征金属中氢扩散最常用的方法之一。可以拟合氧化池中记录的氢原子通量以获得表观扩散率。该系数的大小对氢辅助下的断裂或疲劳现象的动力学具有决定性影响，并且在很大程度上取决于氢在微观结构陷阱中的保留。为了改进扩散系数的数值拟合，使用 FEM 模拟重现了渗透测试，考虑了两种方法：连续 1D 模型，其中陷阱密度，结合能和输入晶格浓度是关键变量和多晶模型，其中明确模拟了晶界处的俘获，包括与晶粒内部不同的偏析因子和扩散系数。结果表明，连续介质模型捕获了捕获延迟，但应该对其进行修改以模拟捕获对稳态通量的影响。根据与 Fickian 扩散的偏差，可以根据不同的制度对渗透行为进行分类。多晶合成渗透显示出偏析对输出通量大小的强烈影响。这种方法也能够模拟短路扩散现象。