Hydriding properties of mechanically alloyed icosahedral phase Ti45Zr38Ni17

The interaction with hydrogen was investigated for mechanochemically synthesised icosahedral phase of the composition Ti45Zr38Ni17. It was demonstrated that, unlike icosahedral phases of the same composition formed as a result of rapid quenching from melt or the annealing of alloys, hydriding of mechanochemically synthesized icosahedral phase at 503 K is not preceded by an induction period and starts at a maximal rate even when hydrogen pressure is less than 0.1 MPa. A diagram of the composition of icosahedral phase versus equilibrium hydrogen pressure (P-T-C diagram) at 503 K was experimentally obtained. Based on published data and the data obtained in our experiments, an assumption was made on the existence of two types of hydrogen positions in the icosahedral structure of the hydrogenated phase. The first type is more energetically bound hydrogen occupying the positions within the structure-forming icosahedral Bergman clusters. The concentration of such hydrogen is approximately corresponding to the relation H/M=1.1. The second type is less bound hydrogen occupying the Linkages between these clusters as solid solution. (C) 2001 Elsevier Science B.V. All rights reserved.