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. (C) 2004 Elsevier Ltd. All rights reserved.