  Various mechanisms have been proposed for hydrogen embrittlement, but the
causation of hydrogen-induced material degradation has remained unclear. This
work shows hydrogen embrittlement due to phase instability (decomposition).
In-situ diffraction measurements revealed metastable hydrides formed in
stainless steel, typically declared as a non-hydride forming material. Hydride
formation is possible by increasing the hydrogen chemical potential during
electrochemical charging and low defect formation energy of hydrogen
interstitials. Our findings demonstrate that hydrogen-induced material
degradation can only be understood if measured in situ and in real-time during
the embrittlement process.
