热暴露对不同组织结构TiAl合金力学性能的影响OA

Ti-44Al-3Mn-0.8(Mo,W)-0.1B-0.1C alloy(at.％)was investigated in this study,from which φ12 mm rods were prepared via vacuum induction melting and hot rolling.By employing different heat treatment regimes,two typical microstructures,near-lamellar and equiaxed,were obtained.The surface microstructural evolution of the two microstructure types after thermal exposure at 750℃ for various durations was systematically examined using EPMA,SEM,and XRD.The mechanical properties before and after thermal exposure were also analysed.The results indicate that after short-term thermal exposure(≤100 h),both microstructures develop a mixed oxide scale on the surface without obvious delamination.Upon long-term thermal exposure(≥200 h),the oxide scales thicken and delaminate.The transition layer in the near-lamellar structure contains a substantial amount of the Laves phase,accompanied by the degradation of α2+γ→γ+βo+Laves near the substrate.In contrast,the transition layer in the equiaxed structure shows only limited Laves phase formation and greater structural stability adjacent to the substrate.Tensile tests reveal that the presence of the surface oxide layer after thermal exposure induced brittle fracture at room temperature.While both microstructure types experience reduced strength at elevated temperatures,ductility is improved.After the surface oxide layer is removed,the strength is partially restored,although the ductility decreases slightly.A comparative assessment demonstrates that,following 500 h of thermal exposure,the equiaxed microstructure exhibitss more stable mechanical properties,whereas the near-lamellar structure experiences a more significant degradation in performance because of lamellar structure breakdown.