Microstructural features and hydrogen diffusion in bcc FeCr alloys: a comparison between the Kelvin probe- and nanohardness based- methods

TL;DR

This study compares Kelvin probe and nanohardness methods to analyze hydrogen diffusion and trapping in FeCr alloys, revealing how microstructural features influence hydrogen behavior relevant to embrittlement.

Contribution

It introduces and validates a nanohardness-based approach for measuring hydrogen diffusion coefficients in FeCr alloys, alongside traditional methods.

Findings

Dislocations, grain boundaries, and Cr atoms act as reversible hydrogen traps.

Hydrogen trapping reduces diffusion coefficients and increases absorbed hydrogen.

The nanohardness method provides consistent diffusion measurements during in situ testing.

Abstract

Hydrogen embrittlement can result in a sudden failure in metallic materials, which is particularly harmful in industrially relevant alloys, such as steels. A more comprehensive understanding of hydrogen interactions with microstructural features is critical for preventing hydrogen-induced damage and promoting a hydrogen-based environment-benign economy. We use the Kelvin probe-based potentiometric hydrogen electrode method and thermal desorption spectroscopy to investigate hydrogen interactions with different hydrogen traps in ferritic FeCr alloys with different chromium contents, dislocation densities, and grain sizes. In addition, we confirm the validity of a novel nanohardness-based diffusion coefficient approach by performing in situ nanoindentation testing. Simultaneous acquisition of the dynamic time-resolved mechanical response of FeCr alloys to hydrogen and the hydrogen diffusivities in these alloys is possible during continuous hydrogen supply. Dislocations, grain boundaries and Cr atoms induce reversible hydrogen trapping sites in these ferritic alloys, leading to the reduction of the hydrogen diffusion coefficients and the increase of the absorbed hydrogen.