Study of the Consolidation and Phase Formation in the γ-TiAl-Based Material Sintered with a TiH₂ Precursor

The hydride powder technique was employed to produce intermetallic TiAl alloys using a mixture of Al and TiH₂ powders. The features peculiar to the consolidation and phase formation in different temperature/kinetic sintering conditions were studied. To impart the required density to TiAl, two methods of refining the initial mixture were employed: (i) high-energy grinding of the components to provide superfine TiH₂ and Al particles and (ii) use of Al₃Ti compounds, easily refined because of extraordinary brittleness, as precursors. In the former method, the phase formation processes are accelerated by the refined powders and positive hydrogen effect. At all sintering temperatures (900–1200°C), intermetallic TiAl with an addition of Ti₃Al is formed after holding for 2–3 h. The material is hardly compacted because of a significant difference in diffusion rates in the Ti–Al system, resulting in the expansion of samples according to the Kirkendall–Frenkel mechanism in the sintering process. In the latter method, the fine TiAl₃ powder, as the starting component, improves the consolidation since the synthesis of Al₃Ti proceeds as an individual process operation. In this case, in optimal sintering modes, the samples have a relatively low porosity of ~10% and a small grain size of 10–20 μm. Mechanical tests demonstrated that the strength and ductility were sensitive to variation in the porosity and grain size. In the best structural states, the powder material produced with the latter method shows the maximum bending strength (σ_b ~ 550 MPa) and the highest compressive strength (σ_c = 1700–1600 MPa) and ductility (δ ~ 20%).