ABSTRACT
The influence of process route on the properties and on the structures of some TiAl-based alloys is reviewed. The thermal stability of these structures is also considered together with the factors that are responsible for the changes in properties in differently processed material. The results reported here confirm that extrusion at high temperatures can give higher strengths than forging, and that for lamellar alloys, the strength increment is mainly due to the very fine lamellar spacing. The current limitations of the production of TiAl alloys using cold-wall furnaces for melting the alloys, either for the production of powders or for the production of castings, is highlighted. Although the process route has a more significant effect on properties than composition, the thermal stability of some processed alloys places a limit on their subsequent operating temperature. Further experimental work is required, aimed at understanding the changes that occur during cooling and/or holding samples at high temperatures, in order to optimize the process route and to develop cost-effective heat treatments of the wide range of TiAl-based alloys that have been developed. The implications of these factors on the potential applications of TiAl-based alloys, particularly in aeroengines, is discussed.
