Effect of Gd Addition on Heat Treatment Microstructure of Wought TiAl

The lamellar microstructures in hot forged Ti-46.5Al-2.5V-1Cr-0.3Ni and Ti-46.5Al-2.5V-1Cr-0.3Ni-0.15Gd alloy were characterized after various heat treatments. It shows that near lamellar microstructures are produced in both alloys at temperature between 1300°C-1320°C. Full lamellar microstructures are transformed at temperature above 1320°C. The average size of lamellar colonies is smaller in the alloy containing Gd than that in the alloy without Gd in near full lamellar microstructures and full lamellar microstructures. The volume fraction of lamellar colonies in Gd-containing alloy is lower than that in Gd-free alloy in near full lamellars. The fluctuation of grain size data in Gd-containing alloys is narrower than that in Gd-free alloy. Gd-rich precipitates in TiAl alloy appear helpful to refine the grain size and improve the uniformity, since they present mostly on the colony boundaries.