Annealing studies of γ-titanium aluminides alloyed with light elements for creep strengthening

A fully-lamellar gamma-titanium aluminide alloy containing carbon and silicon additions has been found to have superior creep resistance. The aging characteristics of this alloy, which also contains Nb, Cr, and W, have been studied by means of transmission electron microscopy techniques and are correlated to the post-crept microstructures. Precipitation of carbides and silicides along gamma/gamma interlamellar boundaries was observed during aging and creep deformation. The driving force for the precipitation reaction is the accommodation of excess amounts of carbon and silicon which have limited solubility in the gamma-matrix. For comparison, the aging behavior of a Ti-46.8Al (at%) alloy containing carbon and boron has been assessed. It is found that the lamellar grain size is significantly smaller than the alloy without boron, but that equiaxed gamma-grains also form during aging. In this alloy, carbides are observed to precipitate homogeneously within gamma-laths and equiaxed grains. (C) 1998 Elsevier Science Limited. All rights reserved.