| Titanium aluminide (TiAl) alloys are attractive materials for use in gas turbine engines, as they possess excellent high temperature properties with the added benefit of having a low density. However, processing these materials in a cost effective and efficient way has been very challenging. Research is now being directed at newly developed beta gamma TiAl alloys that utilize the beta (beta) phase, which becomes soft at high temperature, to improve their hot workability. This thesis explores a powder metallurgy processing route for two beta gamma TiAl alloys. The hot isostatic pressing conditions used to consolidate the powders were optimized to generate a microstructure that would result in excellent hot workability. However, the softening characteristics of the beta phase that improve the hot workability are also detrimental to the high temperature mechanical properties. Therefore, a heat treatment that would be applied following all wrought processing steps was designed to remove the beta phase and develop a fully lamellar microstructure. An aging heat treatment was then used to precipitate fine beta particles at the lamellar interfaces to improve the primary creep properties. |
