Reaction behavior and microstructural evolution of TiAl alloys fabricated by elemental powder metallurgy

A rapid fabrication of pre-sintered TiAl alloy by spark plasma sintering with elemental powders is reported in this study. The reaction behavior between elemental powders and the effect mechanisms of sintering temperature on the microstructure and mechanical properties are systematically investigated. The results show that microstructures are mainly composed of α-Ti, γ-TiAl, α2-Ti3Al, and B2 phases, which vary in volume fraction with different sintering temperatures. The higher sintering temperature promotes the diffusion reactions between elemental powders and hence contributes to the consumption of α-Ti and the generation of particular intermetallic compounds. The average grain sizes of γ-TiAl and α2-Ti3Al phases exhibit the same trend of initially decreasing and then increasing with the increase of sintering temperature. As the sintering temperature increases from 1050 °C to 1250 °C, the density and compression strength of the alloy gradually increase. The densities of the samples all exceed 98% and reach a maximum value of 99.3% at 1250 °C. The compression property of the alloy depends on the synergistic effect of densification and microstructure, which results in a maximum compression strength of 1312 MPa with a fracture strain of 8.9% under the sintering temperature of 1250 °C. All the fracture surfaces exhibit brittle fracture features after compression tests. The relationships between the microstructures and corresponding mechanical properties are discussed in detail.