A gamma titanium aluminide alloy consisting of 46 at % aluminium, 8 at % tantalum and the balance titanium plus incidental impurities has an alpha transus temperature T.sub..alpha. between 1310.degree. C. and 1320.degree. C. The gamma titanium aluminide alloy was heated to a temperature T.sub.1=1330.degree. C. and was held at T.sub.1=1330.degree. C. for 1 hour or longer. The gamma titanium aluminide alloy was air cooled to ambient temperature to allow the massive transformation to go to completion. The gamma titanium aluminide alloy was heated to a temperature T.sub.2=1250.degree. C. to 1290.degree. C. and was held at T.sub.2 for 4 hours. The gamma titanium aluminide alloy was air cooled to ambient temperature. The gamma titanium aluminide alloy has a fine duplex microstructure comprising differently orientated alpha plates in a massively transformed gamma matrix. The heat treatment reduces quenching stresses and allows larger castings to be grain refined.