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

Abstract

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 α₂/γ lamellar colonies with a mean size of 70 µm, 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 β phase after forging suggest that the high-temperature β 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 β phase region, resulting in the formation of a <110>_γ fiber texture where the <110>_γ 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.