The tensile creep behavior of a B₄C-bearing high Nb containing TiAl alloy

In the present paper, the effect of B₄C addition on elevated temperature tensile properties and creep resistance of as-cast Ti–43Al–6Nb–1Mo–1Cr alloy has been characterized. Experimental results reveal that 0.2 at. % B₄C can improve the ultimate tensile strength and elongation of alloy at 800 °C. The steady-state creep rate of alloy with the addition of B₄C decreases from 2.3 × 10⁻⁶ s⁻¹ to 5.2 × 10⁻⁷ s⁻¹ at 800 °C under 300 MPa. The stress exponent (n) and the apparent activation energy (Q_C) of alloy with the addition of B₄C are measured to be 3.18 at 800 °C and 416.410 kJ/mol under 300 MPa, respectively. Combining microstructure observation, the dominant creep deformation mechanisms of Ti–43Al–6Nb–1Mo–1Cr-0.2B₄C alloy at 800 °C under 300 MPa are mechanical twinning and dislocation slipping pinned by solute carbon atoms. During creep, the α₂ lamellar dissolution and α₂/γ interface migration occur simultaneously, and the dynamic recrystallization at colony boundary effectively alleviates the stress concentration resulting from dislocation pile-ups. In addition, the initiation of cavities as well as the propagation and coalescence of cracks are the main creep fracture features. Particularly, TiB can prevent dislocation motion and prolong the crack propagation path to increase creep resistance.