Ultrasonic Treatment Of Melt And Its Effects On Microstructure And Properties Tial Base Allys

TiAl-base alloys attract many attentions due to its outstanding high temperature properties including low density, high specific strength and creep resistance. However, the low ductility and fracture toughness at room temperature largely limit the further development of TiAl alloys. Studies revealed that the grain size of ingots (Al and Mg alloys) can be significantly refined by the applying of ultrasonic treatment. Also, the solidification pores and segregation can be effectively decreased.In this paper, the effect of ultrasonic on the microstructure and mechanical properties of TiAl alloys were studied. The melting and solidification process of TiAl rods were explored. The processing parameters including coil turns, heating power and time were analyzed. Results showed that the melting efficiency is the heighest employing the induction coil with the inner diameter of45mm and the turns of8. When the heating time is over10min or the heating power exceeds10kW, the macrostructure transfers from the transgranular columnar grain to the coarse equiaxed grain. Also, study revealed that the surface quality reaches the best and the solidification defects is the least when the power is6kW and the heating time is8min.The ultrasonic was successfully added into the TiAl melt under the protection of high pure argon. The effects of heating power, heating time and ultrasonic time on the structure and properties of Ti-46A1-0.5W-0.5Si-0.3Y were investigated respectively. Results indicated that the ultrasonic can promote the CET. The α2/γ lamella colony would be refined with the increase of heating power and time. When the ultrasonic time increases from30s ot90s, the colony size decreases from1004.7μmn to88.1μm. Meanwhile, the compressive strength increases from1526MPa to1705MPa. Based on the experimental results and the nucleation theories, the influence mechanism of ultrasonic on the refining TiAl grains was further discussed.The orthogonal experiment containing three factors of heating time, ultrasonic time and ultrasonic power was designed and performed on the Ti-46A1-6Nb alloy. Studies showed that the influence of heating time is the most evident, followed by the ultrasonic time. The smallest colony size is159.4μmn among all solidified samples. The average colony size is181.9μm when the power is7kW and the heating time is8min, and its comprehensive properties is the best that the σbc reaches1158MPa and the Kic is7.38MN×m-3/2. The fracture morphology were analyzed by SEM, and the results indicated that the fracture mechanism of Ti-46Al-6Nb alloy is the combination of cleavage and transcrystalline fracture.