Phase transformations and phase equilibria in a Ti-37% Al-20% Mn alloy

The solid-state phase transformations and phase equilibria in a Ti-37 at% Al-20 at% Mn alloy have been investigated. The alloy was prepared by plasma-are melting and the microstructures of high-temperature-annealed and water-quenched or furnace-cooled samples were studied. The results show that at 1235 degrees C beta-phase and (Mn,Al)(2)Ti (Laves phase) are present whereas below 1000 degrees C the phases (gamma + alpha/alpha(2) + (Mn,Al)(2)Ti) are formed. A comparison between calculated equilibrium phase compositions and values measured by EDXA shows reasonable agreement for the beta, gamma and alpha/alpha(2) phases over a range of temperatures but agreement for the (Mn,Al)(2)Ti phase is less good, particularly at the higher temperatures. The transformation kinetics in this system appear to be sluggish and true equilibrium does not appear to have been achieved in all samples annealed below 1145 degrees C. DTA analysis was also undertaken and the heating thermogram obtained is interpreted with the aid of the calculated phase equilibria. (C) 1999 Elsevier Science Ltd. All rights reserved.