HYDROGEN EVOLUTION FROM CATHODICALLY CHARGED 2-PHASE (TI3AL+TIAL) TITANIUM ALUMINIDES

Ti-45Al and Ti-50Al (at.%) titanium aluminides, whose microstructures consisted of Ti3Al (alpha(2)) and TiAl (gamma), were cathodically hydr ogen-charged in a 5% H2SO4 solution for charging times up to 14.4 ks ( 4 h), and the dissociation process of a hydride and the hydrogen evolu tion process during heating were investigated by thermal analyses (dif ferential thermal analysis and thermal desorption spectroscopy). The h ydride formed during cathodic charging dissociated at the temperature of about 700 K (427 degrees C), and corresponding to the hydride disso ciation, hydrogen gas was evolved from the alloys at the dissociation temperature. In both alloys, accelerated hydrogen evolutions were obse rved at the lower temperatures than that for hydride dissociation. The evolution of hydrogen in the Ti-50Al alloy was extremely accelerated at about 523 K (250 degrees C) and the Ti-45Al at about 600 K (323 deg rees C). The difference in the accelerated evolution temperatures was strongly dependent on the microstructures, in which structural imperfe ctions, such as microvoids or internal cracks, could be formed during cathodic charging. The Ti-45Al alloy picked up about 1.5-times as much hydrogen as the Ti-50Al alloy, and more than 80% of the hydrogen was concentrated at the surface layer up to 20 mu m in depth from the surf ace of the sample.