Directional solidification of intermetallic Ti–46Al–2W–0.5Si alloy in alumina moulds

The microstructure and mechanical properties of intermetallic Ti–46Al–2W–0.5Si (at.%) alloy directionally solidified in alumina moulds were studied. After directional solidification the microstructure consisted of regular α2- and γ-lamellae, elongated B2 particles, Al2O3 particles and fine Ti5Si3 precipitates. Formation of transient cellular-dendritic structure was observed at the growth rates of 2.78×10−6 and 5.56×10−6 m/s. Higher growth rates ranging from 1.39×10−5 to 1.18×10−4 m/s resulted in a regular dendritic structure where the primary dendrite arm spacing decreased with increasing growth rate according to relationship λ1∝V−0.24. The interlamellar spacing decreased with increasing growth rate according to the relationship λ∝V−0.46. The volume fraction of Al2O3 particles increased with increasing temperature of the melt and reaction time. Increasing growth rate resulted in increasing microhardness and compression yield stress of DS ingots. A linear relationship between the microhardness and compression yield stress was determined. The yield stress increased with decreasing interlamellar spacing according to the Hall–Petch relationship.