STUDY OF THE CONSOLIDATION AND PHASE FORMATION IN THE γ-TiAl-BASED MATERIAL SINTERED WITH A TiH₂ PRECURSOR

Abstract

The powder hydride technique is used to produce intermetallic TiAl alloys from a mixture of Al and TiH₂ powders. The features peculiar to the consolidation and phase formation under 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 in the mixing of 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 technique, the phase formation processes are accelerated by the refined powders and a positive effect of hydrogen. At all sintering temperatures (900–1200 °C), intermetallic TiAl with a small addition of Ti₃Al is formed after holding for 2–3 h. The material is hardly compacted because of a significant difference in the diffusion rate in the Ti–Al system, resulting in the swelling of samples according to the Kirkendall–Frenkel mechanism in the initial sintering stages. In the latter technique, 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 technique shows the maximum bending strength (σ_B ~ 550 MPa) and the highest compressive strength (σ_B = 1700–1600 MPa) and ductility (δ ~ 20%).