Sintering Titanium Aluminides with Co Addition

Co additions to titanium aluminides were assessed to decrease the typically high sintering temperatures necessary for the densification of intermetallics. Compositions based on the binary Ti-45Al with ternary Co variations between 1-10 at.% were investigated. The specimens were cylinders with 8 mm diameter prepared using blended elemental powders followed by cold uniaxial pressing. Sintering was carried out under an argon atmosphere at different temperatures ranging from 1100 to 1400 °C for 2 hours in a tube furnace. The results indicated that there was a systematic increase in densification with Co additions. The relative density of the reference material Ti-45Al was approximately 53%, however, Co addition of 10% led to densifications in the order of 80%. A strong effect of decreasing the sintering temperature was achieved with Co additions. The microstructure changed from fully lamellar with 1 at.% Co sintered at 1400 °C to duplex with higher Co additions sintered at 1200 °C. Besides the γ-TiAl and α2-Ti3Al equilibrium phases, the formation of a CoAl2Ti intermetallic was identified. The addition of 7% Co led to the highest hardness of approximately 450 HV.