Effect of spark plasma sintering temperature on microstructure and mechanical properties of an ultrafine grained TiAl intermetallic alloy

The effect of spark plasma sintering (SPS) temperature on the microstructure and mechanical properties of a bulk solid ultrafine grained gamma TiAl alloy produced by SPS of an ultrafine structured Ti/Al composite powder with a nominal composition of Ti-47 at.%Al has been investigated. The Ti/Al composite powder was produced using high energy mechanical milling. It was found that an SPS temperature of 800 °C led to the completion of the reactions needed for reaching the phase equilibrium and formation of a nanostructure with grain sizes in the range of 50-100 nm. However, this SPS temperature was not sufficient to achieve a nearly full density of the compact or a high level of interparticle bonding. Increasing the SPS temperature from 800 to 900 °C caused a significant increase of the density and the level of interparticle bonding while still maintaining grain sizes of <500 nm. The bulk TiAl alloy produced under this condition had a good compression yield strength, fracture strength, bending strength and plastic strain to fracture of 1722, 1963, 610 MPa and 4%, respectively. Increasing the SPS temperature from 900 to 1100 °C caused significant coarsening of the TiAl grains which led to a clear decrease in yield strength and hardness and a slight increase in ductility.