(西南交通大學 材料先進技術教育部重點實驗室，成都 610031)
摘 要: 選取熱暴露(700 ℃，10000 h)前、后的Ti-44.5Al-5Nb-1W-1B(摩爾分數(shù)，%)(5-1-1合金)，對其表面引入不同深度的缺口(0~800 μm)，研究熱暴露對該材料的疲勞性能及缺口損傷容限的影響，以Kitagawa-Takahashi線圖的形式對熱暴露引起的疲勞強化、長裂紋擴展門檻值以及合金在熱暴露影響下對表面損傷的容忍限度進行定量分析。結果表明:熱暴露導致的回火穩(wěn)態(tài)良性效應大于合金顯微組織出現(xiàn)脆化的有害效應，使得熱暴露后無缺口樣品出現(xiàn)疲勞強度提高，而α2層片分解和組織細化能適當提高疲勞長裂紋擴展門檻值。當在熱暴露后引入缺口而無回火效應時，長期熱暴露導致的組織脆化成為控制性因素，材料的缺口敏感性增加，表現(xiàn)為出現(xiàn)短缺口效應的尺寸范圍在熱暴露后明顯增大。
關鍵字: γ-TiAl合金；熱暴露；表面缺口；Kitagawa-Takahashi線圖；疲勞
（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
