Microstructure modification and mechanical performances enhancement of Ti44Al6Nb1Cr alloy by ultrasound treatment

For microstructure modification and performances enhancement, ultrasound treatment was applied in the solidification of Ti44Al6Nb1Cr alloy. The effects of ultrasound treatment on the microstructure characteristic and mechanical performances were studied. The results demonstrate that ultrasound treatment could alleviate the shrinkage defects and improve the quality of casting ingot. The coarse dendritic morphology is modified into small grain structure and the large lamellar colony is refined from 465 μm to 38 μm. The essential elements (Ti, Al) are uniformly redistributed in the lamellar colony, while the alloying elements (Nb, Cr) are aggregated at the lamellar colony boundary leading to micro-segregation. After ultrasound treatment, the microhardness of TiAl alloy is increased from 377 HV to 461 HV and the yield strength is enhanced from 409 MPa to 985 MPa. The ultrasound cavitation enhances the heterogeneous nucleation and the acoustic stream promotes the redistribution of crystal nucleuses, both contributing to grain refinement.