High-temperature oxidation behavior and failure mechanism of Ti₂AlNb alloy in aircraft engines

Ti₂AlNb alloys possess promising application prospects for typical aero-engine components operating at 650-750 ℃, yet they suffer from oxidation embrittlement under the complex high-temperature service environment. In this work, as-rolled Ti₂AlNb alloy is selected as the research material, and as-cast alloy with the identical nominal composition is set as the control group. A series of experiments including 100 h static high-temperature oxidation at 650-800 ℃, room-temperature tensile tests on oxidized specimens, and high-temperature tensile tests at 600-900 ℃ are carried out. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy/high-angle annular dark-field scanning transmission electron microscopy (TEM/HAADF-STEM), and electron backscatter diffraction (EBSD) are employed to characterize oxidation products, interfacial structures, and elemental distribution, so as to clarify the oxidation damage and tensile failure mechanisms of the as-rolled microstructure. The results reveal that after 100 h oxidation at 800 ℃, the mass gain of the rolled alloy reaches 13.7 mg·cm⁻², which is 21.2% higher than that of the as-cast alloy (11.3 mg·cm⁻²). The oxidation rate constant increases from 0.063 for the as-cast alloy to 0.091 for the rolled alloy, representing an increment of 44.4%. A multi-layer oxide scale forms on the rolled alloy, consisting of an outer mixed oxide layer, a middle TiO₂ particle layer and an inner oxygen/nitrogen-enriched embrittlement zone. Microcracks preferentially nucleate at α₂/O phase boundaries and propagate along oxidation channels. After oxidation, at room temperature, the elongation of specimens with oxide layer removed decreases from 12.5% (unoxidized state) to 0.7%-5.0%, while specimens retaining intact oxide layer exhibit a further drop in elongation to 0.4%-0.6%. At high temperature, as the temperature rises from 600 ℃ to 900 ℃, the yield strength declines from 671 MPa to 148 MPa, the ultimate tensile strength decreases from 759 MPa to 169 MPa, and the elongation increases from 14.1% to 161.7%. The tensile failure of as-rolled Ti₂AlNb alloy is jointly governed by oxide layer cracking, oxygen/nitrogen-enriched embrittlement and high-temperature softening.