(1. 中南大學(xué) 粉末冶金國家重點實驗室， 長沙 410083;
2. 鄭州輕金屬研究院， 鄭州 450041;
3. 中南大學(xué) 材料科學(xué)與工程學(xué)院， 長沙 410083)
摘 要: 采用恒應(yīng)變速率和應(yīng)變速率遞增實驗研究了Ti-48Al-2Cr-0.2Mo(摩爾分?jǐn)?shù)，%)合金在常壓空氣中的低溫超塑性變形力學(xué)行為， 并且探討了TiAl基合金的低溫超塑性變形機(jī)理。 研究結(jié)果表明， TiAl基合金的變形組織具有良好的空氣中低溫超塑性變形性能。 在t=900℃， ε·=5×10-4s-1時， 伸長量δ達(dá)到最大值為413%， 即使在較低的溫度（t=800℃）和較高的應(yīng)變速率（ε·=1×10-3s-1）下變形， 伸長量δ值仍然超過300%。 在整個變形區(qū)間m值均大于0.3， mmax為0.78。 當(dāng)t＞900℃或ε·＜5×10-4s-1時， 劇烈氧化導(dǎo)致超塑性變形性能的惡化和脆性斷裂。 在900～950℃之間， TiAl基合金超塑性變形的熱激活機(jī)制發(fā)生轉(zhuǎn)變。 實驗測得TiAl基合金在800～900℃ 時超塑性變形的熱激活能為Qav=178kJ/mol， 這個數(shù)值介于γ-TiAl的蠕變體積激活能和TiAl基合金的空位遷移能之間， 而接近于后者， 因此， TiAl基合金低溫超塑性變形的速率控制機(jī)制是晶界擴(kuò)散。
關(guān)鍵字: TiAl基合金； 超塑性； 速率控制機(jī)制；
HE Yue-hui1, MENG Li-ping3
（1. State Key Laboratory for Powder Metallurgy,
Central South University , Changsha 410083, China.
2. Zhengzhou Light-Metal Institution, Zhengzhou 450041,China;
3. School of Materials Science and Engineering,
Central South University,Changsha 410083, China）
Abstract:Superplastic behaviors of a TiAl based alloy with deformed and duplex microstructure were investigated in air at temperatures ranging from 800℃ to 950℃ and at strain rates ranging from 5×10-5s-1 to 1×10-3s-1. The results show that the TiAl alloy with deformed microstructure exhibits excellent low temperature superplasticity. A maximal elongation of 413% is obtained at 900℃ (at a strain rate of 5×10-4s-1), and the elongation values over 300% are obtained at 800℃(at a strain rate of 5×10-4s-1) or at a strain rate of 1×10-3s-1(at 900℃). The lower superplasticity in duplex microstructure was observed, owing to the larger grain size and the effect of the grain boundary structure and state on the flow. With increased temperatures or decreased strain rates, fracture occurs because of oxidation. The flow softening and the strain hardening are observed in the deformation, a lower rate of strain hardening is corresponding to a larger elongation. The strain rate sensitivity values were examined by incremental strain rate tests. The alloy shows relatively high m value which keeps above 0.3 in the deforming range, the maximal value of m is 0.78. At temperature range from 900℃ to 950℃, the activation mechanism of the superplastic deformation changes, and the activation energy is calculated to be 178kJ/mol at temperature range from 800℃ to 900℃, which is greatly lower than the values of activation energy of volume diffusion in γ-TiAl and in α2-Ti3Al, otherwise closely to the value of activation energy of grain boundary diffusion in γ-TiAl. Therefore, the dominant mechanism during superplatic deformation at temperature range from 800℃ to 900℃ is grain boundary sliding controlled by grain boundary diffusion.
Key words: TiAl based alloy; superplastic deformation; mechanism of rate controlling
