Microstructure and mechanical behavior of a multiphase Al3Ti-based intermetallic alloy

The mechanical properly of the monolithic Ll(2) Al3Ti alloy is unlikely to be improved by further alloying due to the very narrow composition range of the Ll(2) phase in the Al-Ti-X systems. Therefore, we have developed a Nb- modified multiphase Al3Ti-based alloy Al67Mn8Ti24Nb1, which has a Ll(2) mat rix with dispersed Al-3(Ti, Nb) precipitates. High-energy ball milling was employed to fabricate the alloy in comparison with the conventional casting process. A sequence of metastable transitions occurred during the mechanic al milling (MM) process. The microstructures of the bulk materials consolid ated from powers with different starting metastable states have been studie d. It was determined that the alloy consolidated with metastable FCC powder has a much higher strength and better fracture toughness than the cast Al6 7Mn8Ti24Nb1 alloy and the monolithic Ll(2) A(13)Ti alloys. The temperature dependence of yield strength and ductility also shows good results. SEM and TEM investigations were conducted to explore the mechanisms of strengtheni ng and toughening. (C) 2000 Elsevier Science Ltd. All rights reserved.