PHASE-RELATIONS IN TIAL2-BASED TERNARY TITANIUM ALUMINIDES OF IRON OR NICKEL

In order to understand the base binary titanium aluminide of the L1(2)-type ternary titanium aluminides of the composition Ti25X8Al67 (X = Ag, Co, Cr, Fe, Mn, Ni, Pd, Zn) and Ti2CuAl5, six alloys with the composition T34-xFexAl66 and Ti34-xNixAl66 (x = 1, 4 or 8 at.%) have been selected. The alloys were prepared by arc melting and annealed at 1027-degrees-C for 10 days. X-ray powder diffraction, differential thermal analysis (DTA), metallography and microhardness measurements were utilized to reveal the phases present and their microstructural characteristics. The ternary alloys which contain 1 at.% Fe or Ni primarily consist of r-TiAl2 phase (HfGa2 type) with a small amount of the L1(2)-type ternary phase of iron or nickel. An increase in the ternary alloying element to 4 at.% Fe or Ni leads to a two-phase mixture of the r-TiAl2 + L1(2) ternary phase of iron or nickel. The alloys which contain 8 at.% Fe or Ni were found to be primarily the single-phase L1(2)-type ternary titanium aluminide of iron or nickel. The transformation temperatures of the phases are given, based on the DTA data obtained between 500 and 1440-degrees-C with a heating rate of 20-degrees-C min-1. The results are discussed in terms of the current studies on these alloys.