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 beta protide phase. which was measured at the point after desorbing at the plateau region and the thermal stability of the gamma protide phase, which was Measured at the point immediately before desorbing at the desorption region. It was found that the crystal structure of the beta 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 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 DeltaH plots due to existence of the different gamma protides of different thermal stabilities. Namely, this result suggests that site energies of protium in the lattice have a distribution after absorption-desorption cycles.