Pilot processing and microstructure control of high Nb containing TiAl alloy

The investigation of high Nb containing TiAl alloy so far was performed using small heats. In this study, the microstructure control of high Nb containing TiAl alloy was investigated using relatively large forged pancake. The canned forging pancake was successfully gained. The effect of processing and heat treatment on the microstructure was studied using X-ray diffraction, optical microscopy and scanning electron microscopy. Results show that the pancake with a duplex microstructure consists of lamellar colonies, equiaxed γ phase with the grain size of about 20-30 μm and the β(B2) phase at grain boundaries. Energy dispersive spectroscopy analysis shows that the β(B2) phase is enriched in Nb and W. The β(B2) phase was eliminated by heat treatment in α+γ phase region. It is confirmed that the existence of β(B2) phase is due to the segregation of Nb and W. The homogenous near gamma microstructure with the grain size of about 20 μm, and homogeneous refined fully lamellar microstructure with a colony size of about 20 μm was obtained by the special heat treatments.