力學(xué)性能的影響
(西南交通大學(xué) 材料先進(jìn)技術(shù)教育部重點(diǎn)實驗室，成都 610031)
摘 要: 對合金Ti-44Al-4Nb-4Hf-1B在700 ℃大氣氣氛中開展了長達(dá)10 000 h的熱暴露處理，系統(tǒng)地探索和分析含Nb-Hf的TiAl合金的高溫?zé)岱€(wěn)定性，采用透射電鏡和掃描電鏡觀察合金的顯微組織變化并測試相應(yīng)的力學(xué)性能。研究發(fā)現(xiàn)：長期大氣高溫?zé)岜┞秾?dǎo)致合金中α2+γ層片晶團(tuán)內(nèi)的α2層片發(fā)生了一定程度的α2®γ相變：部分α2層片轉(zhuǎn)變成為細(xì)小的γ層片，到10 000 h時，α2層片的原始厚度減少了約一半。長期大氣高溫?zé)岜┞兑矊?dǎo)致合金中α2+γ層片條束上發(fā)生了α2+γ→B2(ω)相變：條束上部分α2+γ消失，代之以微米及亞微米尺度的B2(ω)塊狀相。在10 000 h時，其面積分?jǐn)?shù)達(dá)到8.4%，隨著高溫?zé)岜┞兜闹饾u進(jìn)行，合金的室溫塑性伸長率逐漸降低。在10 000 h時，合金的塑性約為熱暴露前的2/3，表明在復(fù)合含Nb+Hf的TiAl合金中，熱暴露所導(dǎo)致的“釋氧脆化”和“B2+ω生成脆化”的影響有限。復(fù)合含Nb+Hf的TiAl合金具有優(yōu)于單純含Nb的TiAl合金的高溫?zé)岱€(wěn)定性。 長期高溫?zé)岜┞秾辖鸬臄嗔褟?qiáng)度和條件屈服強(qiáng)度沒有明顯的有害影響。在10 000 h時，其條件屈服強(qiáng)度總體上仍保持在600 MPa級別，而合金的室溫疲勞極限還有所提高。
關(guān)鍵字: TiAl合金；熱暴露；相轉(zhuǎn)變；拉伸；疲勞
mechanical properties of Ti-44Al-4Nb-4Hf-1B alloy
（Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University,
Chengdu 610031, China）
Abstract:The Ti-44Al-4Nb-4Hf-1B alloy was exposed at 700 ℃ in air for 10 000 h to assess the thermal stability of TiAl alloy containing Nb-Hf. The changes in microstructure were characterized using transmission electron microscopy and scanning electron microscopy. The corresponding changes in mechanical properties were examined by tensile and fatigue tests. The results show that both the decomposition of α2 lamellae through α2→α2+γ and the formation of B2(ω) through α2+γ→B2(ω) occur inside the α2+γ lamellar colonies. After 10 000 h exposure, the average thickness of α2 lamellae is roughly halved while the area fraction of B2(ω) in micron and submicron size range reaches 8.4%. As a result, the tensile ductility at room temperature reduces by one third after 10 000 h exposure at 700 ℃. The outcome indicates that TiAl alloy containing Nb-Hf demonstrates a higher thermal stability than its counterparts containing Nb due to reduced influence of the “oxygen-release induced embrittlement” and “B2+ω-formation induced embrittlement”. The long-term exposure does not cause detrimental effect on tensile strength and high cycle fatigue limit. After 10 000 h exposure, the proof stress is still at a level of 600 MPa, while the fatigue limit increases noticeably.
Key words: TiAl alloy; thermal exposure; phase transformation; tensile; fatigue
