Abstract
The effect of long-term creep exposure on the microstructure stability of a cast TiAl-based alloy with nominal chemical composition Ti-46Al-2W-0.5Si (at.%) was studied. Constant load tensile creep tests were performed at temperature range 973-1123 K and at applied stresses ranging from 138 to 350 MPa up to 25677 h. The creep curves exhibit short primary creep stage that is directly followed by tertiary creep. For the selected long-term creep regimes, the minimum creep rate is measured to vary from 1.93×10^-9 to 2.83×10^-10s^-1 and depends on the applied stress and temperature. The absence of secondary creep stage is related to stability of initial α₂/γ microstructure and formation of deformation twins. During creep the α₂ (Ti₃ Al) phase in the lamellar and feathery regions transforms partially to the γ (TiAl) phase, needle-like B2 precipitates and occasionally to fine spherical Ti5Si3 silicide particles. Final microstructures of all creep specimens contain four phases α₂+γ+B2+Ti₅Si₃. The applied stresses are shown to accelerate coarsening kinetics of the needle-like B2 precipitates.

Key words
titanium aluminides, TiAl, creep, mechanical properties, microstructure, electron microscopy

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