Abstract:

In order to understand the effect of Mo alloying on the microstructural evolution of TiAl alloy, the as-cast microstructure, heat treated microstructure characteristic, and hot compression microstructure evolution of Ti-44Al alloy have been studied in this work. The as-cast microstructure morphology changes from (γ+α₂) lamellar colony and β/β₀ + γ mixture structure to β/β₀ phase matrix widmannstatten structure, when Mo content increases from 2 at.% to 6 at.%. Affected by the relationship between β phase and α phase, the angles between the lamellar orientation and the block β/β₀ phase are roughly at 0°, 45° and 90°. Comparing with heat treatment microstructure, the hot compression microstructure contains less β/β₀ phase, however, the β/β₀ phase containing 2Mo alloy and 3Mo alloy hot compressed at 1275 °C has the inverse tendency. In addition, (α₂ + γ) colony is decomposed by the discontinuous transformation.

Key words: Phase transformation, Titanium aluminides, Heat treatment, Microstructure evolution, β/β₀ phase;