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

In this work the microstructure and nanohardness of Ti-48at.%Al alloy solidified under different pressures (normal pressure, 2GPa, 4GPa) 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-48at.%Al alloy. However, the microstructure changes under high pressure. With increasing pressure, the volume fraction of interdendritic γ (γ_s) phase decreases and Al concentration in lamellae increases. When the pressure is 4GPa, there is only a little γ_s embedded in lamellar structure. The volume fraction of γ_s phase is approximately 17.0% for normal pressure, 8.73% for 2GPa, 0.69% for 4GPa. The lamellar spacings also decrease with pressure, which are 495nm, 345nm, 227nm under normal pressure, 2GPa, 4GPa, 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 4GPa. When the pressure is 4GPa, the nanohardness increases by 50.2% compared with that of normal pressure.