Thermogravimetric study of hydrogen uptake and desorption in titanium alloys

摘要

Over recent years, titanium has been increasingly used in several industrial fields, such as biomedical implants, structural material in aeronautics, production of energy, chemicals, military applications, luxury products… thanks to a good resistance to corrosion -even in severe conditions- and a low density leading to high specific strength.Enlargement of the use of titanium and its alloys have highlighted new industrial issues and new technological challenges, especially given the sensitivity of titanium to the diffusion of interstitial light elements, which can cause hardening and embrittlement of the material, even at low contents.rnAt room temperature, pure titanium shows an alpha hexagonal close-packed crystal structure which transforms into a beta body-centered cubic structure above 882℃. This transition temperature can be increased or lowered with alloying elements. As an alloying element, hydrogen can be described as a beta-promoting element, meaning that hydrogen solubility is higher in beta than in alpha phase and the alpha-beta transus temperature decreases as the hydrogen level increases.rnBelow 100°C, hydrogen absorption and diffusion in titanium is considered as negligible and has no significant influence on the behaviour of the material. Beyond this temperature, hydrogen absorption can happen and depends on many parameters: temperature, pressure, surface strains and dislocations, properties of the passive layer.rnThis study deals with commercially pure titanium, especially the Ti40 grade, and the determination of the kinetics of hydrogen absorption, diffusion and desorption between 200 and 350°C. Hydrogen uptake has been followed by thermogravimetric analysis (TGA) with different atmospheres and hydrogen partial pressures, and the formation of titanium hydrides has been verified by XRD and XPS analyses. SEM has also been performed to characterize hydraded titanium microstructure.