Hydride formation in two-phase ( Ti3Al + TiAl) titanium aluminides during cathodic charging and its dissociation

Abstract

A (TiAl)H x hydride which has a tetragonal crystal structure with lattice parameters a = 0.452 nm and c = 0.326 nm ( c/ a = 0.721) has been observed in Ti42Al, Ti45Al and Ti50Al (at.%) two-phase (Ti 3Al ( α 2) + TiAl ( γ)) titanium aluminides by cathodic charging in a 5% H 2SO 4 solution. Cracks or pits are also observed within the γ phase regions in the two-phase ( α 2 + γ) coexisting grains (such as lamellar grains) but not within the α 2 phase or single γ grains. Weights of the samples decrease with increasing charging time owing to the crack or pit formation, and this is more drastic in the Ti—50Al alloy than in the Ti—42Al and Ti—45Al alloys. The hydride is thermally stable at temperatures up to about 550 K (277 °C) and dissociates completely at temperatures between 673 K (400 °C) and 723 K (450 °C).