Effects of Sn on the densification and microstructure of a Ti-48Al-2Nb-0.7Mn-0.3Si-1Sn alloy fabricated from cold-pressed powders through vacuum melting

Abstract

The density and microstructure of a modified second-generation γ-TiAl intermetallic alloy with a nominal composition of Ti-48Al-2Nb-0.7Mn-0.3Si-1Sn (at. %) were investigated and compared with similar low-Nb containing alloys reported in the literature. The alloy was successfully fabricated from blended and uniaxial cold-pressed precursor powders and subsequently arc re-melted under vacuum and heat-treated. From the obtained results, the alloy showed improved castability as evidenced by the absence of shrinkage cavities and the highest relative density of 99.87%. In as-cast condition, the microstructure comprised fine-grained dendritic structures of γ-phase and γ + α2 lamellae with a mean grain size of about 49 μm which transformed into a well-developed duplex structure consisting of γ grains and γ + α2 lamellae, and traces of Ti5Si3 precipitates after heat treatment. The alloy exhibited a more significant grain refinement in as-cast condition than its counterparts reported previously.