Carbon content driven high temperature γ-α2 interface modifications and stability in Ti–46Al–4Nb intermetallic alloy

The effect of carbon addition on the microstructure modifications and hardness response of a two-phase lamellar Ti–46Al–4Nb intermetallic alloy was studied. The alloy was heat treated as to have an initial tow-phase refined lamellar microstructure consisting of α2 laths and γ phase characterized by nanometric wide twinning. The effect of carbon in solid solution in the α2 phase and the onset of the H–Ti2AlC phase precipitation within the γ phase was addressed. A threshold carbon limit of C ≅ 3000 wt ppm was identified as lower limit solute concentration for the precipitation initiation of the H phase particles. The major alloy hardening factors were identified as the refined interlamellar spacing, the fine twinning and the amount of carbon in solid solution. The role of H phase formation on the alloy hardening with carbon content was addressed and it was essentially such to induce a hardening saturation effect.