The metallurgical preparation and microstructure of as-cast Ti-45Al-2W-xC (in at.%) alloys were investigated. Five alloys with carbon content ranging from 0.38 to 1.96 at.% were prepared by vacuum induction melting (VIM) in graphite crucibles, followed by centrifugal casting into graphite moulds. A master 15W-85Al (at.%) alloy with a relatively low melting point and TiC powder were used to facilitate fast dissolution of W during VIM and to achieve the designed content of C in the as-cast alloys, respectively. The increase in the content of C affects the solidification path of the studied alloys. Differential thermal analysis (DTA) and microstructural observations show that the alloys with carbon content up to 0.75 at.% solidify with β primary phase and their dendritic as-cast microstructure consists of the α2(Ti3Al) + γ(TiAl) lamellar regions, retained B2 phase enriched by W and single γ phase formed in the interdendritic region. The increase in the content of C above 0.75 at.% leads to the formation of primary lathe-shaped Ti2AlC carbides, which act as effective heterogeneous nucleation sites of β dendrites during the solidification and grain refinement of the alloys with 1.15 and 1.96 at.% C. The increase in the content of C leads to an increase in Vickers hardness and elastic modulus in the alloys containing 1.96 at.% C.
Keywords: TiAl; carbides; intermetallics; microstructure; solidification; vacuum induction melting.