Homogenization treatment of high Nb containing TiAl alloys with as-cast and as-forged microstructures

The effect of heat treatment on the microstructure evolution of a high Nb containing TiAl alloy has been studied. The results indicate that β-segregation, α-segregation and S-segregation in the as-cast and as-forged alloys can be effectively eliminated at the temperature above T_α (1350-1400°C) for long holding time (12-24 h) and the full lamellar (FL) microstructure is gained. For the two alloys, the lamellar colony sizes are 120 μm and 2000 μm, respectively after heat treatment at 1400°C for 12 h. Meanwhile, the sizes are 210 μm and 3000 μm, respectively at 1350°C for 24 h. To get a fine homogenous microstructure, the primary as-cast alloy is first subjected to preheat treatment for eliminating the segregations. After the preheat treatment, the alloy is processed by the multi-step canned forging to attain the microstructure with fine grain size.