Ti-Cr-V alloys with a BCC structure have high protium (hydrogen atom) capacities. In considering practical use, protium absorption-desorption cyclic properties become an important problem. In this paper, the cyclic properties in high-low hydrogen pressure regions are investigated in order to clarify the change of the crystal structure and the protium capacities of appeared phases of the β, γ protides in the Ti-Cr-V alloys and Ti-Cr-Mo, Ti-Cr-Al alloys. As a result, it was found that the crystal structure of the β protide phase changed from a BCC structure to a BCT structure by increasing the cycle number in the Ti-Cr-Mo, Ti-Cr-Al alloys similar to the Ti-Cr-V alloys. This result suggests that the lattice will be hard to be contracted gradually along the a-axis direction of the absorbing process with an increasing cycle number. It was also found that β protide phase in the alloys which have bad cyclic properties became stable with an increasing cycle number because the low hydrogen pressure region P-C-isotherm curves shifted to the low pressure side with an increasing cycle number. The major reason of this result is considered to be the accumulation of the lattice defects in the alloys with an increasing cycle number.
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