材料期刊网

The structural relationship between the hydride phases in Ti-Mo-H solid solution system (Mo content up to 15 at% in the alloy) during dehydrogenation process under annealing has been studied by conventional and in situ X-ray powder diffraction and transmission electron microscopy (TEM) analysis. During dehydrogenation, the saturated hydrides of the Ti-Mo alloys with fcc delta-phase structure transfer into bcc beta-phase at higher temperatures. An associated hydrogen concentration reduction for the delta-phase hydride is observed in the process. However, as the hydrogen concentrations decrease to certain values (H/M similar to 1.1-1.7), the unsaturated delta-phase formed at high temperature would become unstable at lower temperature, and transfer into a tetragonal phase (denoted the epsilon-phase here). Unlike that of the e-phase in Ti-H system, the phase transition does not occur for the saturated delta-phase with hydrogen concentration close to the stoichiometric limit. The hydrogen concentration of this epsilon-phase hydride is in between that of the tetragonal gamma and epsilon-phase in Ti-H system, but more close to the gamma-phase. The occurrence region of this epsilon-phase expands along with the increase of the Mo content in the alloys. The phase has a lattice similar to that of the e-phase in Ti-H system with corresponding fct unit-cell c/a < 1. (c) 2007 Published by Elsevier B.V.