Multiscale Elastic Modulus Characterization of TiFeMn, an Iron-Titanium-Manganese Alloy Dedicated to Hydrogen Storage.

Hydrogen storage in intermetallic compounds, known as solid-state storage, relies on a phase change by the metal alloy. This phenomenon causes a violent change in volume at the crystalline scale, inducing a change of volume for the millimetric particles and, with time, important stresses on the tanks. It is thus necessary to know the mechanical behavior of the material to report these phenomena and improve the tanks' reliability. The present study deals with the mechanical characterization of TiFeMn alloy at different scales. First, the elastic modulus was measured by compression tests of cylindrical samples. The estimated macroscopic elastic modulus was about 198 GPa, with high variability, from 163 to 229 GPa. Secondly, ultrasonic elastic characterization together with instrumented indentation allowed an estimation of both Young's modulus and Poisson's ratio at 269 GPa and 0.29, respectively. Finally, the nanoindentation results, combined with SEM imaging and EDS analyses, revealed that several metallurgical phases coexist below the particle scale. Four distinct domains in terms of elasticity were clearly identified. The coherence of all these estimations is discussed and interpreted considering the true microstructure of the material and the defects present in the different samples.