Effect of high temperature hydrogen treatment in titanium alloys

Hydrogen treatment of materials (HTM) is a powerful method for both microstructure and properties modifications of two-phase titanium alloys (α+β). HTM consists of several stages and during these stages some structural transformations occur. The idea of this treatment is based on accumulation after each consecutive cycle microstructure defecting in microstructure as a result of execution of a single heating-cooling cycle in hydrogen presence. In titanium alloys, hydrogen most often appears as hydrides. First stage - hydrogenation of titanium alloy at the temperature of two-phase area (under high pressure or by glow discharge in hydrogen atmosphere) to produce rich in hydrogen the βH - phase and titanium hydride δ. Second stage consists in allotropic change and the titanium hydride δ - phase decomposition at the temperature of the β - phase area. Third stage is annealing at the temperature of the α+β area. During this stage the transformation βH to α + titanium hydride δ occurs. Fourth stage - dehydrogenation in high vacuum at the temperature of the two-phase area which causes recrystallisation of the microstructure. After hydrogen treatment grain refinement and division of lamellar microstructure α - phase was observed (especially in the surface of specimens).