THEORETICAL-ANALYSIS OF ORDERING IN TI3AL-BASED ALLOYS .2. THE EFFECTOF HYDROGEN ON THE STABILITY OF TI3AL INTERMETALLIC COMPOUND

A thermodynamical model of hydrogen solution in Ti3Al was proposed. Th e free energy and the long-range order were calculated as a function o f the composition and temperature. Hydrogen enhances the the long-rang e order degree caused by the formation of the alpha(2)-phase by nuclea tion and growth mechanism. The temperature of the equilibrium between ordered and the disordered phases increases with hydrogen concentratio n, and the range in which the formation of the alpha(2)-phase occurs b y the nucleation and growth mechanism (I-order) broadens. The above ef fects facilitate the control of the structure of the Ti3Al-based alloy s by reversible hydrogen alloying.