(西南交通大学 材料先进技术教育部重点实验室，成都 610031)
摘 要: 选取热暴露(700 ℃，10000 h)前、后的Ti-44.5Al-5Nb-1W-1B(摩尔分数，%)(5-1-1合金)，对其表面引入不同深度的缺口(0~800 μm)，研究热暴露对该材料的疲劳性能及缺口损伤容限的影响，以Kitagawa-Takahashi线图的形式对热暴露引起的疲劳强化、长裂纹扩展门槛值以及合金在热暴露影响下对表面损伤的容忍限度进行定量分析。结果表明:热暴露导致的回火稳态良性效应大于合金显微组织出现脆化的有害效应，使得热暴露后无缺口样品出现疲劳强度提高，而α2层片分解和组织细化能适当提高疲劳长裂纹扩展门槛值。当在热暴露后引入缺口而无回火效应时，长期热暴露导致的组织脆化成为控制性因素，材料的缺口敏感性增加，表现为出现短缺口效应的尺寸范围在热暴露后明显增大。
关键字: γ-TiAl合金；热暴露；表面缺口；Kitagawa-Takahashi线图；疲劳
（Key Laboratory of Advanced Technologies of Materials, Ministry of Education,
Southwest Jiaotong University, Chengdu 610031, China）
Abstract:Single edge through thickness notch of different depths (0-800 μm) was introduced to the surface of Ti-44Al-5Nb-1W-1B alloy (5-1-1 alloy) before and after the thermal exposure at 700 ℃ for 10000 h. The effects of thermal exposure on the fatigue behaviour and the surface defect tolerance capability were studied. The exposure-induced fatigue strengthening, the fatigue threshold of long cracks and the surface defect tolerance under thermal exposure were quantitatively analysed and discussed in the form of Kitagawa-Takahashi diagram. The results show that the positive effect of the thermal exposure-induced tempering stability is greater than the harmful effect of the microstructural embrittlement. The fatigue strength of the non-notched is therefore improved after thermal exposure. On the other hand, the increase in threshold stress for long fatigue crack growth after the long-term exposure is attributed to the refinement of α2 lamellae. The introduction of the short notches after thermal exposure (hereby no tempering effect) has caused increased notch sensitivity, causing an increased notch size range within which the fatigue strength decreases significantly, due to microstructural embrittlement induced by the long-term thermal exposure.
Key words: γ-TiAl alloy; thermal exposure; surface crack; Kitagawa-Takahashi diagram; fatigue
