The fine-grained gamma titanium aluminide of the composition Ti-46Al-1.5(Mo, Cr)-0.2Si (concentration in at%) with the coexisting α_2-Ti_3Al phase finely dispersed throughout the γ-TiAl matrix exhibits enhanced superplasticity at strain rates (ε) of 5 · 10~(-4) ≤ ε ≤ 10~(-2) s~(-1) in the temperature regime of 975 °C to 1050 °C. The recorded strain-rate-sensitivity exponents are relatively high in the range of 0.55 ≤ m ≤ 0.76. Maximum superplastic elongations of SSP ≈1055 % were achieved at strain rates of 8 · 10~(-3) s~(-1). Quasi superplastic behaviour occurs also at higher deformation rates up to 2 · 10~(-1) s~(-1) and at temperatures of about 1180°C to 1280°C. This refers to high-strain-rate superplasticity, which is in particular suitable for near net-shape forming operations like superplastic die forging of engine parts, such as valves, connecting rods, and compressor or low-pressure turbine blades. The TiAl (Mo, Cr, Si)-base alloys under investigation exhibit a high specific Young's modulus of about 43 GPa (g/ccm)~(-1) and a room temperature elastic modulus of E_(RT) ≈ 170+-3 GPa. The yield strength is of about 1050 MPa, and a room temperature ductility up to ε_(PL)≈3 % was achieved in the thermomechanically processed -extruded- state. The finegrained equiaxed microstructure consists of dynamically recrystallized γ-TiAl (Mo, Cr, Si) matrix grains of 1 to 3 μm in size and of smaller α_2-Ti_3Al (Mo, Cr, Si) grains of less than 0.5 μm in size finely dispersed throughout the matrix. This microstructure is a prerequisite for achieving enhanced superplasticity.
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