Abstract
In this work, the diffusion equation for the gas-solid system is revised to describe the non-uniform distribution of hydrogen in steels. The first attempt to build a theoretical and general model and to describe the diffusion process as driven by a chemical potential gradient is made. A linear elastic solid body and ideal gas, diffusing into it, are considered. At this stage, we neglect any traps and non-linear effects. The coupled diffusion-elastic boundary problem is solved for the case of the cylinder under the tensile loads. The obtained results correspond to the experimental ones. Based on them, the assumptions about the correctness of the model and its further improvement are suggested.
Highlights
The problem of hydrogen embrittlement is a well-known one [1]: the adsorption and transport of the hydrogen from the external environment lead to the degradation of the mechanical properties of the steel
As we aim to build a general and theoretical model, we start with the simplest case and neglect plasticity, multichannel diffusion and trapping, which in case of non-equilibrium thermodynamics approach can be added as terms in chemical potential
There was no need to use exact parameters because our main goal is to see how the model takes into account stress-strain state and if it is appropriate to describe high hydrogen concentration gradients and the so-called boundary layer
Summary
The problem of hydrogen embrittlement is a well-known one [1]: the adsorption and transport of the hydrogen from the external environment lead to the degradation of the mechanical properties of the steel. To describe the process of hydrogen diffusion from the external environment into the steel, one cannot be satisfied with only Fick’s laws of diffusion, as many side effects begin to play a significant role ([2,3,4]) Various approaches, taking such effects into account, exist. The already existing models describe particular experiments, usually are phenomenological and do not take into account all the factors affecting the hydrogen absorption. These models are verified on small concentration gradients and cannot be used to describe recent experimental results
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