Study of the mechanisms of metal-hydrogen reactions in multicomponent alloys with C14 - hexagonal laves phases

Abstract

More recently, multicomponent alloys such as high-entropy alloys - in special the alloys containing single C14 laves phase with hexagonal structure - have been tested as hydrogen storage materials and very promising results have been reported such as high hydrogen storage capacity with fast kinetics at room and moderate temperatures without the need of any activation procedure. In spite of the good results obtained so far, very few studies have been dedicated to the understanding of the mechanisms of hydrogen absorption and desorption in multicomponent alloys with the majority presence of the C14 laves phase. In this research project, we intend to investigate the mechanisms of the metal-hydrogen reaction during the hydrogen absorption and desorption processes in multicomponent alloys with the majority presence of the C14 hexagonal laves phase by means of in-situ X-ray diffraction measurements. We seek a better understanding of the stability and reversibility of the C14 hexagonal laves phase, which is still lacking in the literature. Multicomponent alloys with the majority presence of the C14 laves phase in different ratios between the alloying elements of AB, AB2, A1,5B and AB1,2 systems (where A represents the elements with high affinity to absorb hydrogen, such as: Ti, Zr , Nb and V; while B represents the elements with low affinity with hydrogen, such as: Fe, Cr, Mn, Ni, Co) will be properly selected through the evaluation of empirical thermodynamic parameters and thermodynamic calculations through the CALPHAD method (Thermocalc Software) and subsequently prepared by arc melting under controlled atmosphere. After processing the alloys, the effects of applied a severe plastic deformation technique such as High-Pressure Torsion (HPT) will be evaluated in order to improve the hydrogen storage properties. The selected alloys including or not the HPT step will be characterized after exposure to hydrogen at different doses and stages of absorption and desorption by different characterization techniques including in-situ X-ray diffraction, scanning and transmission electron microscopy which will provide relevant information on the phase stability and reversibility of C14 laves phase as a function of the proportion of A and B elements. This research proposal is the result of the national and international collaboration underway between the main researcher of this proposal and the researchers from the Federal University of São Carlos (UFSCAR), the Brazilian Synchrotron Light Laboratory (LNLS) from the Brazilian Center for Research in Energy and Materials (CNPEM) and Kyushu University (Japan), which has resulted in joint works and publications on the subject, and has even allowed us to make significant progress from design, processing to the characterization of new alloys with excellent properties for hydrogen storage. (AU)