In-situ neutron diffraction study of phase stability and equilibria in the Ti-rich part of the Ti-Al binary system

Three alloys with composition range of Ti-(25-35)Al (atomic %) were in-situ investigated using neutron diffraction to clarify the phase stability and equilibria in the Ti-rich part of the Ti-Al binary system. The phase transformation sequences of these three alloys were identified based on the neutron diffraction results and differential scanning calorimetry. No superstructure diffraction of beta(o) has been found in the neutron diffraction patterns. It is concluded that the beta(o) phase in the examined composition range is thermodynamically unstable. Based on the phase transformation sequences of these three alloys, combining the characters of congruent type relationship and peritectoid type relationship, the phase equilibria among beta, alpha and alpha(2) phases were confirmed as a peritectoid type, with two peritectoid reactions, i.e., beta-alpha ->alpha(2) and beta +alpha(2)->alpha.