Microstructural evolution of TiAl base alloy during three-stepped thermo-mechanical treatment

Abstract

A TiAl base alloy ingot with a height-to-diameter ratio of 2.2 was broken down by multiple step canned forging. The microstructures after every deformation and subsequent recrystallization were observed by optical microscopy. Results show that at the first step the reduction should be carefully controlled in case of double-bulge and crack of the ingot. After the first annealing, recrystallization occurred at the deformed grain boundaries and inside the grain. The recrystallized microstructure is favorable for further deformation. After the second deformation and annealing, coarsening of the lamellae occurred and the microstructure became equiaxed. By the final deformation and subsequent recrystallization, the coarse lamellar colony can be refined to about 20 µm, and homogeneous microstructure was obtained from the ingot with a large initial height-to-diameter ratio.

Keywords

TiAl base alloy / hot forging / microstructure

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