Evolution of the microstructure and nanohardness of Ti–48 at.%Al alloy solidified under high pressure

In this work the microstructure and nanohardness of Ti–48 at.%Al alloy solidified under different pressures (normal pressure, 2 GPa, 4 GPa) were experimental investigated by using a tungsten-carbide six-anvil apparatus. The results indicate that high pressure does not change the phase constitution of Ti–48 at.%Al alloy. However, the microstructure changes under high pressure. With increasing pressure, the volume fraction of interdendritic γ (γs) phase decreases and Al concentration in lamellae increases. When the pressure is 4 GPa, there is only a little γs embedded in lamellar structure. The volume fraction of γs phase is approximately 17.0% for normal pressure, 8.73% for 2 GPa, 0.69% for 4 GPa. The lamellar spacings also decrease with pressure, which are 495 nm, 345 nm, 227 nm under normal pressure, 2 GPa, 4 GPa, respectively. The change in nanohardness was discussed based on the microstructural observations. It shows a certain increase of the nanohardness as the pressure increases from normal pressure to 4 GPa. When the pressure is 4 GPa, the nanohardness increases by 50.2% compared with that of normal pressure.

► The microstructure of Ti–48Al alloy changes under high pressure.
► With increasing pressure, the amount of γs phase decreases.
► High pressure leads to the decreasing of lamellar spacing.
► The nanohardness of lamellar structure increases with pressure.