超温热暴露对铸造 TiAl-4822 合金显微组织和力学性能的影响

Effects of hyperthermal exposure on microstructures and mechanical properties of casting TiAl-4822 alloys

摘要

探讨 Ti-48Al-2Cr-2Nb 合金（简称为 4822 合金）在 800～950 ℃短时超温热暴露后显微组织和力学性能的变化规律，研究热暴露温度和时间对 4822 合金显微组织，室、高温拉伸性能及高温持久性能的影响。结果表明，800～950 ℃超温热暴露后 4822 合金组织中 α₂/γ 片层团中 α₂ 相溶解形成粗大的 γ 片层。随着温度的提升，α₂ 相溶解数量越来越多，α₂/γ 片层组织末端粗化，且向相邻片层生长。900 ℃热暴露后在片层团与等轴 γ 晶粒的边界处有球形 B2 相析出，950 ℃热暴露后片层团内粗大的 γ 片层内部析出细小的 B2 相，B2 相数量增多。随着热暴露时间的延长，块状 α₂ 相内析出极细的 γ 片层且数量增加，片层团晶界处出现的等轴 γ 晶粒逐步长大，片层团内部出现的等轴 γ 晶粒数量增多。经 850 ℃/10 min、850 ℃/120 min、900 ℃/10 min 热暴露后，合金的室、高温屈服强度均增加，室、高温断后伸长率均下降，950 ℃/10 min 热暴露后合金的室、温断后伸长率为（2.4±0.55）%，比原始状态提升 5.73%；经 850 ℃/10 min、850 ℃/120 min、900 ℃/10 min 热暴露后合金在 650 ℃/400 MPa 条件和 700 ℃/350 MPa 条件的持久寿命均增加，但在 850 ℃/120 min 热暴露后合金在 650 ℃/400 MPa 条件下的持久寿命为（14.85±3.55）h，比原始状态下降 94.02%。

Abstract

This work investigates the alterations in the microstructure and mechanical properties of the Ti-48Al-2Cr-2Nb alloy (referred to as 4822 alloy) following simulated short-term superheated service at 800-950 ℃. The research focuses on the effects of thermal exposure temperature and holding time on the microstructure, room-temperature and high-temperature tensile properties, and high-temperature endurance properties of 4822 alloy. The results reveal that after exposure at 800-950 ℃, the α ₂ phase within the α₂/γ lamellar colonies dissolves, forming coarse γ lamellae. As the thermal exposure time increases, the dissolution of the α₂ phase becomes more pronounced, the ends of the α₂/γ lamellar structures coarsen, and the lamellae grow into adjacent colonies. After treatment at 900 ℃, spherical B2 precipitates form at the boundaries between lamellar colonies and equiaxed γ grains. At 950 ℃, fine B2 precipitates appear within the coarse γ lamellae inside the colonies, and the number of B2 precipitates increases. Prolonging the exposure time leads to the precipitation of extremely fine γ lamellae within blocky α₂ phases, with their quantity increasing; equiaxed γ grains at colony boundaries gradually grow, and the number of equiaxed γ grains within the colonies also rises. After thermal exposure at 850 ℃/10 min, 850 ℃/120 min, and 900 ℃/10 min, both the room and high-temperature yield strengths of the alloy increase, while the room and high-temperature elongations decrease. However, after thermal exposure at 950 ℃/10 min, the room-temperature elongation of the alloy is (2.4±0.55)%, representing an increase of 5.73% compared to its original state. After thermal exposure at 850 ℃/10 min, 850 ℃/120 min, and 900 ℃/10 min, the stress rupture lives of the alloy under both 650 ℃/400 MPa and 700 ℃/350 MPa conditions are extended. However, after thermal exposure at 850 ℃/120 min, the stress rupture life under 650 ℃/400 MPa is (14.85±3.55) h, which decreased by 94.02% compared to its original state.

关键词

Ti-Al 系金属间化合物 / 热暴露 / TiAl 合金 / 精密铸造 / 显微组织 / 力学性能

Key words

Ti-Al intermetallics / thermal exposure / TiAl alloy / precision casting / microstructure / mechanical property

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基金资助

国家自然科学基金(52371015)

稳定支持项目(KZ0C231525)