Hydride precipitation in vapor deposited Ti thin films

Titanium hydrides having two different crystal structures were observed in α–Ti thin films grown epitaxially on sapphire substrates by e-beam physical vapor deposition. One of the hydrides (γ-hydride) had a face-centered tetragonal structure (c/a > 1) with an ordered arrangement of hydrogen atoms. The second hydride formed was the fcc δ-hydride. The γ-hydride grew as platelets in the α–Ti lattice with {10$\overline 1$0}_Ti habit planes, whereas the γ-hydrides formed directly on the sapphire substrate parallel to the (0001)_Ti. These hydrides are one of the principal causes of film decohesion.