Influence of heat treatment on microstructure and nanohardness of TiAl alloy solidified under high pressure

The Ti-48at.%Al alloy solidified under different pressures was prepared using a tungsten-carbide six-anvil apparatus and then heat treated at different temperatures. The effect of heat treatment on microstructure and mechanical properties of high pressure solidified Ti-48Al alloy was investigated. The results showed that the phase constitution of the Ti-48Al alloy solidified under high pressure did not change after heat treatment. After 1,100 °C/12 h AC (air cooling), the value of c/a showed a slight increase. The Widmanstätten structure was formed in the samples solidified under 2 GPa and 4 GPa. More defects were found in the high-pressure samples. The volume fraction of α2 particles increased with an increase in pressure. After 1,150 °C/4 h AC, the discontinuous coarsening phenomenon could only be found in the 4 GPa solidified samples. The formation of α2 phase can lead to the increase of nanohardness. Compared with the samples before heat treatment, the nanohardness increased about 1.0–1.2 GPa.