Creep and microstructure of near-gamma TiAl alloys

Creep strength and microstructure of Ti–48Al–2Cr–2Nb–1B and Ti–46Al–2W–0.5Si–(0.7B) alloys are compared. The influence of a prior-to-creep heat treatment on the initial microstructure is investigated. The isothermally forged and heat treated Ti–48Al–2Cr–2Nb–1B alloy was tested in nearly lamellar and equiaxed modifications while the cast and HIP-ped Ti–46Al–2W–0.5Si alloy was either nearly lamellar or duplex before creep. All these microstructural variants were crept in tension at 1023 K and at different applied stresses. Experimental results obtained in the present study suggest that, in spite of creep strength variations resulting from the different microstructural states, the Ti–46Al–2W–0.5Si alloy performs better than the Ti–48Al–2Cr–2Nb–1B alloy. Transmission electron microscopy analysis provided evidence that W- and Si-rich phases that precipitate both, on the lamellar boundaries and inside the gamma grains, contribute to the superior creep strength of the Ti–46Al–2W–0.5Si alloy.