Gigapascal yield strength at 900 °C in a boron-free TiAl complex alloy having excellent room temperature formability

Abstract

A newly designed boron-free alloy, Ti₅₀Al₄₅Nb_2.5Mo_1.25Ta_0.5W_0.5V_0.25 (TiAl–complex alloy (CA), ρ = 4.12 ± 0.015 g cm⁻³), exhibited a compressive yield strength (YS) of 1.080 ± 0.029 GPa at 900 °C, along with excellent room temperature (RT) strength–formability (YS = 1.107 ± 0.038 GPa, ε = 0.12 ± 2) synergy in the as-cast state. Moreover, the as-cast TiAl CA exhibited controlled mass gain (1.46 ± 0.07 mg cm⁻²) at 900 °C upon isothermal exposure for 96 hours, displaying excellent oxidation resistance. The improved strength–formability synergy at RT is attributed to a refined γ-L1₀-dominated three-phase microstructure undergoing twinning and deformation-induced (γ → α₂) transformation, in addition to slip-based plasticity. The unusual yet desired β₀ phase dissolution (minimal phase fraction) at 900 °C provides exceptionally high YS, whereas the formation of dense Al₂O₃ + TiO₂ layers on the surface results in controlled oxidation. Thus, the similar YS (∼1.1 GPa) of TiAl–CA at RT and 900 °C ensures exceptional microstructural stability in comparison with the pre-existing γ-TiAl and Ni-based superalloys, making it a potential candidate for fuel-efficient aero-engine applications.