A novel method for grain refinement and microstructure modification in TiAl alloy by ultrasonic vibration

In this paper, the ultrasonic vibration treatment was applied to the TiAl alloy melt during the solidification aiming at modifying the coarse microstructure and improving the mechanical properties. Effects of ultrasonic vibration on the microstructure and mechanical properties of TiAl are elaborately studied. The results show that the grain size was refined from 545 μm to 96 μm, the yield strength was improved from 419 MPa to 854 MPa, and the coarse dendrite structure was modified into fine non-dendrite grains after ultrasonic vibration. Given the high melt viscosity and narrow liquid-solid temperature range, the predominant refinement mechanism of ultrasonic vibration for TiAl is the cavitation-enhanced nucleation due to the nucleus activation and/or heightened supercooling.