Creep properties of near γ-TiAl+W with a lamellar microstructure

Abstract

It is well established that the microstructure and mechanical properties of near [gamma]-TiAl alloys are dependent on heat treatment, with the [alpha][sub 2] + [gamma] lamellar or fully transformed'' microstructure providing the best creep resistance. However it is unclear if the enhanced creep resistance is due to the large grain size typical of the fully transformed microstructure or is an attribute to the lamellar [alpha][sub 2] + [gamma] morphology. Separation of the grain size and structural affects is difficult due to the rapid grain growth kinetics during heat treatment in the single phase [alpha] region, which is required to generate the fully transformed structure. However, the creep properties of a relatively fine grained fully transformed microstructure and the affect of lamellar grain size in the range 600--1,200 [mu]m have recently been reported, with the conclusion that creep behavior is controlled by a dislocation climb mechanism. The primary purpose of the work described in this paper is to determine the creep properties of TiAl+W with lamellar grain sizes of <500 [mu]m. Lamellar microstructures with grain sizes of <500 [mu]m are of particular interest, since the reduced grain size improved tensile ductility. TiAl+W was selected for this work since the W additionmore » reduces the grain growth kinetics during heat treatment in the single phase [alpha] region.« less