Destructive Hydrogenation and Recombination of α₂-Ti₃Al Alloy: Production of Solid Nanocomposites and Coatings with Improved Properties. I.Mechanism of Destructive Hydrogenation of Ti₃Al

Abstract

It is shown that α₂-Ti₃Al alloy and hydrogen interact at 298–1533 K in accordance with the destructive hydrogenation reaction whose products are titanium hydride and intermetallic compounds rich in aluminum. The structure phase mechanism of α₂-Ti₃Al destructive hydrogenation is as follows. Hydrogen dissolves in Ti₃Al, thus leading to disordering of its crystalline structure. Then hydrogen interacts with titanium, but not with the disordered alloy, according to the following scheme: α-Ti (hcp) → α-TiH_x (hcp) → β-TiH_y(bcc) → TiH_1.9(fcc) → TiH₂(bct). The intermetallic compounds rich in aluminum show up when new stoichiometric concentrations of titanium and aluminum form in accordance with Ti–Al phase diagram. Solid composites with nanosized components result from the destructive hydrogenation of Ti₃A at 973 K for 1 and 4 h. Their phase compositions are Ti₃Al–(α-TiH–Ti_3–xAl) and ((α-Ti–H_x)–(β-Ti-H_y)–TiH_1.9(fcc)–TiH₂(bct))–(Ti₃Al–TiAl–TiAl₂), respectively.