Formation of Non-equilibrium Phases by Repeated Forging of Al-Ti Alloys

Al-5, 10, 20, 25 and 30 at%Ti mixed powders were repeatedly forged by our developed bi-axial compression in the Ar atomosphere at 200∼300°C. This new processing enables us to synthesize and consolidate the bulk metals with non-equilibrium phases and little amounts of inpurities such as O, N and Fe. In case of 120 shots repeated forging of Al-Ti mixed powders, non-equilibrium phase of L12 type crystal structure Al3Ti compound was formed and only of L12 phase was observed in the composition of Al-20 and 25 at%Ti. L12 phase, heated for 1 h at 400∼500°C, is transformed into non-equilibrium DO23 type Al3Ti and further to equilibrium phase, DO22 type Al3Ti by heating at above 600°C. Lattice parameter of L12 phase was 0.398-0.399 nm and L12 and DO23 phases have very fine particles in size of 5∼20 nm. A forged Al-20 at%Ti specimen shows a remarkable age-hardening property; hardness chaneged to Hv450 in the sample heated at 350∼450°C from Hv200 before heating.