Neutron and in situ X-ray investigation of hydrogen intake in titanium-based cubic alloys

The structure of nanocrystalline Ti:Ru:Fe (2 - gamma:(1 + gamma)/2:(1 + y)/ 2) obtained by high-energy ball milling has been studied by X-ray and neutr on diffraction as a function of the Ti content, for gamma varying from 0.00 to 1.00 by step of 0.25, using Rietveld refinement; analysis. When gamma = 0.00, a nanocrystalline metastable B2 cubic phase is formed, with most of the la site occupied by Ti atoms and the Ib site occupied by either Fe or R u atoms. When decreasing the Ti content, the B2 structure becomes less stab le. A preferential replacement of Ti by Fe on the la occurs and leads to th e precipitation of hcp Ru. In situ X-ray diffraction measurements under hyd rogen at high pressure were also made. In all cases, a shift of the diffrac tion peaks of the B2 structure toward the smaller 2 theta values was observ ed. This shift is totally reversible upon removing hydrogen. It indicates t hat hydrogen is absorbed into the materials. The volume increase of the B2 structure varies according to the Ti content, reflecting the fact that less hydrogen is absorbed when Ti is reduced. Assuming that the volume occupied by a single hydrogen atom is similar to 2.5 D-3, the hydrogen content; of the various nanocrystalline Ti:Ru:Fe (2 - gamma:(1 + gamma)/2:(1 + gamma)/2 ) is calculated from the volume increase of the unit cell of the correspond ing materials.