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

The mechanical property of the monolithic Ll2 Al3Ti alloy is unlikely to be improved by further alloying due to the very narrow composition range of the Ll2 phase in the Al–Ti–X systems. Therefore, we have developed a Nb-modified multiphase Al3Ti-based alloy Al67Mn8Ti24Nb1, which has a Ll2 matrix with dispersed Al3(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 mechanical milling (MM) process. The microstructures of the bulk materials consolidated from powers with different starting metastable states have been studied. It was determined that the alloy consolidated with metastable FCC powder has a much higher strength and better fracture toughness than the cast Al67Mn8Ti24Nb1 alloy and the monolithic Ll2 Al3Ti alloys. The temperature dependence of yield strength and ductility also shows good results. SEM and TEM investigations were conducted to explore the mechanisms of strengthening and toughening.