The use of Hydrogen combustion as energy source for aerospace applications would result in the exposition of critical parts, such as turbojet injectors, to complex thermomechanical loading in the presence of high-pressure hydrogen gas. However, it’s well known that, a long-term exposure to hydrogen can lead to a deterioration in the mechanical properties of metals and a premature failure known as hydrogen embrittlement.

Hydrogen embrittlement (HE) is strongly material and loading dependent, and can operate through several mechanisms. These mechanisms include Hydrogen Enhanced Localized Plasticity (HELP), Hydrogen Enhanced Decohesion (HEDE), Adsorption-Induced Dislocation-Emission (AIDE), Hydrogen Enhanced Strain-Induced Vacancy (HESIV) and their synergistic effects.

The goal of this study is to characterize how HE will affect additively manufactured Inconel 718, a key alloy for designing complex turbojets parts. Specifically, the study focuses on the characterization of fatigue life reduction induced by H intake, and the underlying mechanisms.

The Inconel 718 used in this study is obtained by Laser Powder Bed Fusion, L-PBF, followed by homogenization and aging to annihilate the columnar grain structure and the anisotropic microstructure characteristic of L-PBF and to precipitate the second-phase particles of the material.

Mechanical tests are carried out on the specimens precharged with hydrogen gas in a furnace operating at 400bar and a temperature of 200°C, to study the effect of hydrogen concentration on the alloy’s cyclic viscoplastic behaviour. Hydrogen thermal desorption mass spectroscopy are carried out to measure the quantity (concentration) of hydrogen in the material and to identify the quantity of H trapped and in solution.

After the specimens precharging with hydrogen gas, monotonic loading and Oligo-cyclic fatigue tests under isothermal conditions are carried out for a specified temperature range from ambient to intermediate temperature, in order to assess the impact of Hydrogen pre-charging on the fatigue life and mechanical properties of the material in this temperature range. The cyclic loading carried out help to identify the material’s cyclic viscoplastic behaviour.

To better understand the role of microstructure on the deformation mechanisms associated with the presence of hydrogen, micromechanical tensile tests under SEM are also carried. Nano-indentation and electron microscopy characterizations (TEM, SEM) are also envisaged, which will be correlated with thermal desorption spectrometry (TDS) analyses of hydrogen concentration and states (trapping detrapping, interstitial diffusion) to study hydrogen segregation in the specimens tested, as well as its effect on the microscopic plasticity of the material.