顯微結(jié)構(gòu)及力學性能的影響
(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: 采用掃描電鏡、透射電鏡以及拉伸和高周疲勞等試驗手段研究10 000 h、700 ℃大氣熱暴露過程對Ti-44Al-4Nb-4Zr-0.2Si-1B合金顯微結(jié)構(gòu)和力學性能的影響。結(jié)果表明：復合含Nb-Zr的TiAl合金的α2+γ層片組織顯示出較高的熱力學穩(wěn)定性，合金的α2+γ層片晶團在熱暴露過程中，α2→γ和α2+γ→B2(ω)相變并不普遍。合金中B2(ω)晶粒由若干微米胞構(gòu)成，長期的高溫熱暴露導致胞壁處具有較高有序度的D88相結(jié)構(gòu)的ω顆粒明顯長大，且胞內(nèi)也大量析出這種脆性的D88相結(jié)構(gòu)的ω顆粒；同時，在B2(ω)晶內(nèi)還析出微米級別的γ相，這是該合金 10 000 h熱暴露過程后脆性明顯增加的主要原因。此外，該合金拉伸強度和條件屈服強度在熱暴露過程中變化不大，室溫疲勞極限甚至還有所提高。
關鍵字: 鈦鋁合金；熱暴露；顯微結(jié)構(gòu)；力學性能
mechanical properties of Ti-44Al-4Nb-4Zr-0.2Si-1B alloy
（Key Laboratory of Advanced Technologies of Materials, Ministry of Education,
Southwest Jiaotong University, Chengdu 610031, China）
Abstract:The effect of thermal exposure at 700 ℃ in air for 10 000 h on the microstructure and mechanical properties of Ti-44Al-4Nb-4Zr-0.2Si-1B alloy was investigated using scanning electron microscopy and transmission electron microscopy and tensile and high cycle fatigue test. The results show that the decomposition of α2 lamellae through α2→γ and the formation of B2(ω) through α2+γ→B2(ω) are not prevail inside the α2+γ colonies. This tends to suggest that the α2+γ lamellae are at a high level of thermodynamic stability. B2(ω) grains consist of many micron-sized cells, in which ω particles with D88 highly ordered structure in cell-wall regions grow significantly during the long-term exposure. Such D88-ω particles also form widely inside the cells. Moreover, the micron-sized equiaxed γ phase also precipitates from B2(ω) grains. The tensile ductility in the exposed alloy reduces remarkably. While the long-term exposure does not cause detrimental effect on tensile strength and high cycle fatigue limit. The proof stress is still at level of larger than 600 MPa, while fatigue limit increases noticeably after 10 000 h exposure.
Key words: TiAl-based alloy; thermal exposure; microstructure; mechanical property
