Effect of Al content on the microstructure and mechanical properties of γ-TiAl alloy fabricated by twin-wire plasma arc additive manufacturing system

TiAl alloys are considered as promising high temperature structural materials. However, the inherent brittleness makes it difficult to be processed. In the present research, TiAl alloys with different Al content are fabricated successfully using an innovative twin-wire plasma arc additive manufacturing system. The effect of Al level on the phase composition, microstructure characteristics, microhardness and tensile properties of as-deposited TiAl alloy is investigated in detail. The results show that the α2 phase content exhibits increase tendency with the decrease of Al level, and the α2 phase content is higher in the top region than that in the middle region. The tetragonal ratio c/a of γ phase tends to reduce with the decrease of Al content. The microstructure characteristics also present obvious difference for as-deposited TiAl alloys. The lamellar spacing gradually decreases with the decrease of Al concentration. With decreasing Al level, the microhardness of alloy tends to increase. In addition, the as-deposited Ti-48 Al (at.%) alloy exhibits much better tensile properties than other TiAl alloys due to optimum microstructure characteristics. The findings provide a valuable reference for additively manufactured TiAl alloy with proper composition ratio.