Influence of hydrogen on the γ-matrix lattice parameters of a Ni-based superalloy – A synchrotron diffraction study

Hydrogen, as an energy carrier, is expected to play a significant role in future mobility. The objective of this study was to investigate the hydrogen uptake of the Ni-based superalloy VDM® Alloy 780 through electrochemical charging, using high-energy synchrotron X-ray diffraction (HEXRD). It is shown that the incorporation of hydrogen at interstitial positions in the crystal lattice leads to a slight increase in the lattice parameters compared to hydrogen-free analogs. In-situ HEXRD measurements showed a convergence of the lattice parameters at elevated temperatures, indicating the reversibility of hydrogenation through diffusion and subsequent effusion of hydrogen. Hot gas extraction (HGE) measurements were conducted to quantify hydrogen and complement the diffraction data, showing that prolonged electrochemical charging leads to increased hydrogen content. Hydrogen quantification at different temperatures confirmed increasing diffusion with temperature, i.e. higher measured hydrogen values at elevated temperatures. Additionally, tensile tests were conducted to evaluate the influence of hydrogen on the alloy during deformation. Fractographic analysis via SEM showed that, for the hydrogen-treated specimen, cleavage fracture occurred in the vicinity of the surface, whereas the reference sample displayed typical ductile fracture patterns over the entire fracture surface. • Interstitial hydrogen increases the γ phase lattice parameters of a superalloy. • Lattice expansion is reversible, shown by in situ high-energy XRD. • Hot gas extraction for hydrogen quantification, and as complement to XRD. • Hydrogen effusion studied at various temperatures via hot gas extraction. • Slight reduction of elongation at fracture observed in hydrogen-loaded specimens.