Mechanical properties of nanostructured intermetallic alloys in the systems TiAl-X and TiAl₃-X

The mechanical properties of nano and microcrystalline TiAl-X and TiAl₃-X alloys have been investigated by means of compression tests. X refers to different additions of Cr, Mn, and Fe. All alloys have been produced by mechanical alloying and sintering techniques. TiAl-X alloys have nanostructures consisting of two phases i.e. γ and α₂. TiAl₃-X alloys are formed by a single phase with an L1₂ structure. Compression tests give rise to high values of flow strength in all alloys. TiAl-X alloys with average grain sizes ranging from 100 - 150 nm show flow stresses that vary from 2 to 3 GPa at room temperature. Lower flow stresses (0.7 to 2 GPa) have been measured at higher temperatures (up to 873 K). A relatively high compression ductility has been observed for these alloys. In the case of TiAl₃-X alloys no ductility was found at room temperature with fracture strengths between 0.8 and 2.5 GPa. The average grain size of the as-sintered alloys ranged from 20 to 42 nm. The TiAl₃-Fe and TiAl₃-Cr alloys have been annealed at 1373 K in order to promote grain growth. Such alloys with coarser grains (average size ranging from 430 to 720 nm) showed also high flow strengths (0.7 - 1.2 GPa at room temperature) and considerable compression ductility.