Abstract
Creep properties of two cast TiAl-based alloys with nominal chemical composition Ti-46Al-2W-0.5Si and Ti-45Al-2W-0.6Si-0.7B (in at.%) were investigated. The constant load creep tests were performed in air at applied stresses ranging from 200 to 390 MPa in the temperature range from 973 to 1073 K. For both alloys, the minimum creep rate is found to depend strongly on the applied stress and temperature. The power law stress exponents of minimum creep rate and the apparent activation energies for creep are determined. The initial microstructure of the alloys is unstable. In the lamellar and feathery regions, the α ₂ (Ti₃Al)-phase transforms to the γ (TiAl)-phase, B2 particles and fine Ti₅Si₃ precipitates. The main microstructural change observed in the γ-rich region was precipitation of fine Ti₅Si₃ particles. Ordinary dislocations in the γ matrix dominate the deformation microstructures at creep strains lower than 1.5 %. For both alloys at low creep strains, the kinetics of the creep deformation is proposed to be controlled by non-conservative motion of dislocations. The alloy doped by boron shows superior creep resistance when compared to that of boron-free counterpart alloy.

Key words
titanium aluminides, TiAl, creep properties, microstructure

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