SANS investigation of precipitation hardening of two-phase γ-TiAl alloys.

Two-phase titanium aluminide alloys are being considered as lightweight materials to replace nickel-based superalloys in some high-temperature aero-engine applications. However, at an intended service temperature of 700 °C the strength and creep resistance of the titanium aluminides are inferior to those shown by superalloys. Therefore, precipitation-hardening treatments using carbon additions were tested for an improvement of the strength. Ageing of a Ti-48.5 at. % Al-0.4 at. % C alloy for 24 h at 750 °C after a solution treatment for 4 h at 1250 °C, followed by quenching, leads to the formation of perovskite-type precipitates, significantly improving the high-temperature strength. The size distribution and volume fraction of the perovskite precipitates were measured using small-angle neutron scattering (SANS). The results after extended ageing periods show that although the precipitate size distribution changes significantly, the effect on the yield strength is relatively small. [ABSTRACT FROM AUTHOR]