Effect of forging on the microstructure and texture of a high Nb containing γ-TiAl alloy

The effect of forging on the microstructure and texture evolution of a high Nb containing Ti-45Al-7Nb-0.3W (at.%) alloy was investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that the as-cast alloy is mainly composed of alpha(2)/gamma lamellar colonies with a mean size of 70 mu m, but the hot-forged pancake displays a near duplex microstructure (DP). Kinking and bending of lamellar colonies, deformation twinning and dynamic recrystallization (DRX) occur during hot forging. Meanwhile, dense dislocations in the beta phase after forging suggest that the high-temperature beta phase with a disordered structure is favorable for improving the hot-workability of the alloy. Unlike the common TiAl casting texture, the solidification process of the investigated as-cast alloy with high Nb content is completely via the beta phase region, resulting in the formation of a <110>(gamma) fiber texture where the <110>(gamma) aligns parallel to the heat-flow direction. In comparison, the relatively strong <001> and weak <302> texture components in the as-forged alloy are attributed to the deformation twinning. After annealing, static recrystallization occurs at the twin boundary and intersections, which weakens the deformation texture.