THE STRUCTURE OF THE TI2AL PHASE AND ITS RELATIONSHIP WITH TIAL AND TI3AL PHASES IN THE INTERMETALLIC COMPOUND TI48.3AL51.7

The metastable Ti2Al phase is usually formed in the Al-rich TiAl inter metallic compounds. The structure of this Ti2Al phase and the relation ship with TiAl(gamma) and Ti3Al(alpha2) phases were investigated. The Ti2Al phase is hexagonal with lattice parameters a = 0.301 nm and c = 1.431 nm and stacking sequence AB'CBC'B. The interface between Ti2Al a nd gamma-phase is a geometric plane parallel to the {111}gamma or (000 1)Ti2Al. Along the gamma-Ti2Al interface some mismatch dislocations ar e arranged with a period of 4.2 nm. These mismatch dislocations have a half atomic plane in the gamma-phase parallel to another {111} plane and do not form ledges along the interface. The Ti2Al and alpha2-plate s often coexist in the gamma-matrix and their interface is always para llel to the {1010BAR}alpha2 plane. The atomic structure of the Ti2Al p hase and the characteristics of the alpha2-Ti2Al interface may imply t hat the Ti2Al phase is an interim phase during the transformation of t he alpha2-phase from they-phase and an outline model of this transform ation mechanism is suggested.