Fabrication and Microstructure Optimization of TiAl Castings Using a Combined Melting/Pouring/Heat Treatment Device

In this paper, a vacuum melting furnace which combines melting, pouring, mold preheating and heat treatment was designed and built, for the purpose of fabrication and microstructure optimization of TiAl castings. The apparatus provides the accurate control of pouring, mold preheating and subsequent heat treatment with various cooling rates, which makes the complete process from casting to final heat treatment can be carried out in one equipment and avoids the sample transfer process from casting to heat treatment device. The performance of the furnace was evaluated by casting the Ti–48Al–2Cr–2Nb and high-Nb-containing TiAl sheet and rod components. The X-ray detection images and scanning electron microscope results showed that the cavity and segregation were eliminated obviously. Significantly, an optimal nearly lamellar microstructure and fine fully lamellar microstructure were obtained, respectively. In addition, the transmission electron microscopy results show the lamellar spacing size after moving out of the heat treatment chamber is thinner than that cooling in the chamber. The results are of interest to researchers devoted to technical innovations and modifications for TiAl investment casting at the industrial scale.