The interplay between thermomigration and stress-driven hydrogen transport in metals

TL;DR

This paper develops a thermodynamically consistent model to analyze how thermomigration and stress-driven mechanisms influence hydrogen transport in metals, revealing thermomigration's dominance in heat exchangers and its interplay with stress effects.

Contribution

It introduces a mechanistic framework for hydrogen thermomigration within a finite element model, providing new insights into hydrogen redistribution in metals under thermal and stress conditions.

Findings

Thermomigration often dominates hydrogen redistribution in heat exchangers.

Stress-driven transport becomes significant near sharp stress concentrators.

A graphical method helps identify the dominant transport mechanism quickly.

Abstract

Thermomigration is the driving force for hydrogen transport due to a temperature gradient. It can compete with hydrogen transport induced by stress gradients. While stress-driven hydrogen migration is well established, thermomigration remains comparatively underexplored, largely due to limited mechanistic understanding and a scarcity of experimental data. In this work, we develop a thermodynamically consistent framework for hydrogen transport, incorporating a mechanistic model for thermomigration. This is implemented within a finite element framework using an effective chemical potential. Using case studies of iron and nickel heat exchangers and zirconium alloy nuclear fuel cladding, we quantify the competing and synergistic effects of thermomigration and stress-driven transport. We show that thermomigration often dominates hydrogen redistribution in heat-carrying components, even in the presence of significant thermal incompatibility stresses. However, stress-driven transport is shown to become decisive near sharp stress concentrators. A graphical method is introduced to rapidly identify the dominant transport mechanism without requiring fully coupled simulations. The results provide practical guidance for assessing hydrogen redistribution and embrittlement risk in heat-carrying structural components.