Surface modifications of titanium-based alloys using mechanical/chemical treatments to enhance hydride formation kinetics

Hydrogen is one of the promising alternatives energy carrier in the transition from fossil fuels to renewable energy. However, the storage of the hydrogen is a crucial challenge. One viable option is the solid-state storage with metal hydrides. This type of storage requires activation of the metal to absorb hydrogen and, in addition, there are several kinetics barriers that slow down the hydriding reaction. Mechanical deformation and the use of catalyzers are considered as methods to activate and improve the kinetics of the hydriding process. The aim of this thesis is to better understand the mechanisms of hydrogen absorption by exploring various strategies involving microstructural modifications by mechanical deformation and surface chemical changes. Titanium has been used as a model material for studying hydriding mechanisms where three complementary approaches were investigated. The first approach involved using plastic deformation through cold-rolling of commercial α-titanium to introduce varying amounts of deformation, with the aim of understanding its effect on hydrogen sorption kinetics. It was demonstrated that increasing the level of deformation improves absorption kinetics, primarily due to a higher fraction of high-angle grain boundaries, a favorable (00.2) crystallographic texture, and a faster reduction of the native surface oxide layer. In addition, the effect of plastic deformation on the hydride microstructure, cracking behavior and hydride formation mechanisms was studied. Hydride grain size and the resulting cracking were found to strongly depend on cold-rolling conditions. Hydrogenation in cold- rolled titanium was heterogeneous, and similarities in hydride formation mechanisms with zirconium were observed at low cold-rolling ratios. The second approach was surface chemical modification, by adsorption of an Fe thin layer to study the surface evolution of a Fe/Ti model system during activation. It was shown that titanium diffusion and the restructuring of the iron layer into clusters greatly influence hydrogen molecule dissociation. A high density of small iron clusters was found to enhance absorption kinetics, confirming the catalytic effect of iron. Finally, a multiphase TiFeMn alloy capable of absorbing hydrogen at room temperature was characterized to gain new insights into the reasons behind its effective 3 activation. XPS and TEM analyses revealed that different phases have distinct surface oxide compositions. In particular, the Ti₄Fe₂O phase, enriched in iron, may have a catalytic role thus enabling hydrogen activation at room temperature. These observations highlight the crucial importance of the surface local chemical composition, and phase interfaces in sorption mechanisms. 

Keywords : Plastic deformation, surface modification, titanium hydride, activation, absorption kinetics.

Jury members :

Reviewers: 

• Ms. MONNIER Judith Professeure, ICMPE Paris, France

• Mr. MERCIER Dimitri Chargé de Recherche, IRCP Paris, France

Examiners: 

• Ms. de RANGO Patricia Directrice de recherche, Institut Néel Grenoble, France

• Mr. POLANSKI Marek Professeur, Université militaire de technologie de Varsovie, Pologne

• Mr. EDALATI Kaveh Professeur, Université de Kyushu, Japon

• Mr. SAUVAGE Xavier Directeur de Recherche, GPM Rouen, France

Supervisor : 

• Mr. GROSDIDIER Thierry Professeur, LEM3 Metz, France

Co-supervisor: 

• Mr. LEDIEU Julian Directeur de Recherche, IJL Nancy, France