Effect of absorption-desorption cycles on structure and stability of protides in Ti-Cr-V alloys

Ti-Cr-V alloys with a BCC structure have high protium capacities, but it is known that the cyclic properties for the alloys change with varying V content. In this paper, the cyclic properties of the Ti-Cr-V alloys are investigated in view of the crystal structure of the β protide phase, which was measured at the point after desorbing at the plateau region and the thermal stability of the γ protide phase, which was measured at the point immediately before desorbing at the desorption region. It was found that the crystal structure of the β phase was changed from BCC phase to BCT phase and the c/a increased with increasing the cycle number. This difference of the crystal structure of the β phase suggests that the lattice can't gradually contract to a-axis direction at absorbing process with increasing the cycle number. Furthermore, it was found that the absorption-desorption cycle process causes the declined slope of the ΔH plots due to existence of the different γ protides of different thermal stabilities. Namely, this result suggests that site energies of protium in the lattice have a distribution after absorption-desorption cycles.