Analysis of the influence of microstructural traps on hydrogen assisted fatigue

TL;DR

This study models how microstructural traps affect hydrogen diffusion and embrittlement under cyclic loads, revealing that increasing beneficial trap densities can mitigate hydrogen-assisted fatigue.

Contribution

A novel multi-trap hydrogen transport model integrated into finite element analysis, highlighting the role of trap density in fatigue resistance.

Findings

Maximum lattice hydrogen concentration is sensitive to loading frequency and diffusion coefficient ratio.

Higher trap densities can reduce hydrogen embrittlement during cyclic loading.

Beneficial traps are effective in designing fatigue-resistant alloys.

Abstract

We investigate the influence of microstructural traps on hydrogen diffusion and embrittlement in the presence of cyclic loads. A mechanistic, multi-trap model for hydrogen transport is developed, implemented into a finite element framework, and used to capture the variation of crack tip lattice and trapped hydrogen concentrations as a function of the loading frequency, the trap binding energies and the trap densities. We show that the maximum value attained by the lattice hydrogen concentration during the cyclic analysis exhibits a notable sensitivity to the ratio between the loading frequency and the effective diffusion coefficient. This is observed for both hydrogen pre-charged samples (closed-systems) and samples exposed to a permanent source of hydrogen (open-systems). Experiments are used to determine the critical concentration for embrittlement, by mapping the range of frequencies where the output is the same as testing in inert environments. We then quantitatively investigate and discuss the implications of developing materials with higher trap densities in mitigating embrittlement in the presence of cyclic loads. It is shown that, unlike the static case, increasing the density of "beneficial traps" is a viable strategy in designing alloys resistant to hydrogen assisted fatigue for both closed- and open-systems.