Mechanical alloying of the Ti-Al system in a hydrogen gas atmosphere and their subsequent consolidation

Three kinds of Ti-Al powders, Ti₇₂Al₂₈, Ti₅₇Al₄₃ and Ti₄₈Al₅₂, mechanically alloyed by a planetary ball mill in a hydrogen gas atmosphere (0.1 MPa) for alloying time of 30 h were consolidated by cold isostatic pressing and sintering in a vacuum. The densities and Vickers hardness of the consolidated samples were measured and then were compared with those obtained from powders mechanically alloyed in an argon gas atmosphere as well as those without mechanical alloying (MA). The hydrogen atmosphere enhanced the solid-solid reaction accompanying with the assistance of dynamical process of MA and accelerated the formation of amorphous phase or the refinement of the powders without forming a hydride phase after a longer MA process. The microstructures of the consolidated samples after MA were not dependent on gas atmosphere and could be estimated from the Ti-Al binary phase diagram. Higher density as well as higher Vickers hardness could be expected in the consolidated samples obtained after MA in hydrogen gas atmosphere.