航空发动机Ti2AlNb合金高温氧化行为与失效机理OA

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.