Formation of ternary L12 intermetallic compound and phase relation in the Al-Ti-Fe system

Abstract

Sintering of elemental powders and conventional arc-melting were used to form ternary L12 intermetallic compounds in the Al-Ti-Fe system. The L12 phase field and phase equilibria surrounding the L12 phase in the temperature range of interest were established. Two isothermal sections at 1423 and 1273 K were determined from metallography, X-ray diffraction and electron probe microanalyses. The compositions of L12 phase field, the center compositions of oval-shaped region, were about 28Ti-8Fe-64Al and 27Ti-9Fe-64Al compositions at 1423 and 1273 K, respectively. Thus the L12 phases had less ternary and more titanium than those reported in the other Al-Ti-X (X = Mn, Cr) systems. Besides the L12 phase, the pertinent second phases were TiAl (L10-type), TiAl2 (HfGa2-type), Ti2Al5 (28 atoms/unit cell-type), Al3Ti (D022-type), C14 (Laves phase, MgZn2-type), and D8a (cubic, Mn23Th6-type). The solubility of iron in TiAl2 phase was about 2 and 3 mol% at 1423 and 1273 K, respectively. The TiAl2 phase is more stable at 1273 K and can coexist with L12, TiAl, C14, and D8a phases in separate phase fields. Thus in the isothermal section at 1273 K, no two-phase equilibrium between the TiAl and L12 phases exists. This impedes the development of bonding between TiAl and L12 alloys in coating applications.