Mechanical and microstructural changes of Ti and Ti–6Al–4V alloy induced by the absorption and desorption of hydrogen

Vickers microhardness tests and X-ray diffraction analysis (XRD) were used to study the mechanical and the structural properties of Ti and the Ti–6Al–4V alloy during the hydrogen absorption–desorption process. Ti and the Ti–6Al–4V alloy were hydrogenated at different temperatures (150, 300, 450, 500, 550, 600, 650 and 750 °C), reaching maximum hydrogen concentration of (2.95 ± 0.24) × 1022 H/cm3 for Ti and (2.82 ± 0.22) × 1022 H/cm3 for the alloy. Hardness of both metals increased with hydrogen absorption, but a decrease in the Vickers microhardness number was observed in both materials when they started to loose hydrogen. The XRD analysis showed changes in the crystal size in those samples with large amounts of hydrogen, as well as changes in crystal orientation in the Ti–6Al–4V alloy induced by the hydrogen absorption.