本文選題：TC21合金 + 超塑性變形　； 參考：《南昌航空大學》2015年碩士論文

【摘要】：TC21合金是我國自主研發(fā)的新型鈦合金,經(jīng)過適當?shù)葴劐懺旒盁崽幚砜色@得高強韌的網(wǎng)籃組織,具有較好的損傷容限性。已有研究表明TC21合金具有優(yōu)良的超塑性,但其在超塑性成形過程中,尤其高溫及低應變速率下組織會發(fā)生聚集長大,組織不同于等溫鍛造,而TC21合金從超塑變形到熱處理過程的組織演變規(guī)律尚未明確,超塑性變形后的組織能否通過熱處理得到高強韌性的組織亟待研究。本文對TC21合金進行超塑性變形,再通過不同的熱處理制度對超塑性變形后的組織進行改善,研究了TC21合金的超塑性變形行為和熱處理對其顯微組織的影響。主要研究內(nèi)容和結(jié)論如下:(1)采用恒應變速率法對TC21合金進行超塑性變形,研究超塑性變形過程的流變應力行為及顯微組織演變規(guī)律,建立相關(guān)流變應力數(shù)學模型。TC21合金在超塑性變形過程中組織發(fā)生明顯動態(tài)再結(jié)晶,隨著變形溫度的升高,或應變速率的降低,α相含量逐漸減少,動態(tài)再結(jié)晶晶粒發(fā)生聚集長大,合金延伸率降低;當應變速率較低,變形溫度較高時,流變應力曲線趨于平穩(wěn),軟化機制以動態(tài)回復為主,材料表現(xiàn)出較好的超塑性。通過計算推導得到TC21合金兩相區(qū)超塑性變形激活能和應力指數(shù)分別為329.20 kJ/mol和2.3677;采用Arrhenius模型建立了合金流變應力-應變本構(gòu)方程,并通過1stOpt軟件進行修正,最大誤差為11.22%,平均誤差為3.51%。(2)對TC21合金超塑性變形后的組織進行三重熱處理,研究熱處理參數(shù)對TC21合金超塑性變形后組織的影響。第一重熱處理溫度對TC21合金最終組織中的晶界α相產(chǎn)生影響。隨著第一重熱處理溫度升高,長條晶界α相增多,較為粗大筆直;當?shù)谝恢責崽幚頊囟仍谙嘧凕c附近時,最終組織析出的晶界α相較少。熱處理過程析出的次生α相隨著第二重熱處理溫度的升高或冷卻速率的降低而尺寸增大,呈針狀;二次生α相隨第三重熱處理溫度的升高而粗大;當冷卻速率較慢時(爐冷),α相呈集束片狀在晶界和晶粒內(nèi)析出,顯微組織為粗大魏氏體組織;當冷卻速率較快時,得到長條針狀馬氏體α''和亞穩(wěn)β相,亞穩(wěn)β相經(jīng)第三重熱處理后彌散析出細小針狀α相,呈網(wǎng)籃狀。(3)三重熱處理可使TC21合金在β相區(qū)或兩相區(qū)超塑性變形的組織大部分獲得網(wǎng)籃組織,但熱處理后的組織中仍會存在部分的長條晶界α相。本文改善TC21合金超塑性變形后組織的最佳熱處理工藝為:(940~970)℃/1h AC+(900~930)℃/1h AC+590℃/4h AC。
[Abstract]:TC21 alloy is a new type of titanium alloy developed independently in China. After proper isothermal forging and heat treatment, high strength and toughness can be obtained, which has good damage tolerance. It has been shown that TC21 alloy has excellent superplasticity, but in superplastic forming process, especially at high temperature and low strain rate, the microstructure will gather and grow, and the microstructure is different from isothermal forging. However, the microstructure evolution of TC21 alloy from superplastic deformation to heat treatment is not clear, and it is urgent to study whether the microstructure of superplastic deformation can be obtained by heat treatment. In this paper, the superplastic deformation of TC21 alloy was carried out, and the microstructure after superplastic deformation was improved by different heat treatment systems. The superplastic deformation behavior of TC21 alloy and the effect of heat treatment on its microstructure were studied. The main contents and conclusions are as follows: (1) superplastic deformation of TC21 alloy is carried out by constant strain rate method, and the rheological stress behavior and microstructure evolution of superplastic deformation process are studied. The dynamic recrystallization occurred in TC21 alloy during superplastic deformation. With the increase of deformation temperature or the decrease of strain rate, the 偽 phase content gradually decreased, and the dynamic recrystallization grain aggregate and grow. When the strain rate is low and the deformation temperature is high, the rheological stress curve tends to be stable, the softening mechanism is mainly dynamic recovery, and the material shows better superplasticity. The activation energy and stress exponent of superplastic deformation in two-phase region of TC21 alloy are 329.20 kJ/mol and 2.3677, respectively. The constitutive equation of rheological stress-strain of TC21 alloy is established by Arrhenius model and modified by 1stOpt software. The maximum error is 11.22 and the average error is 3.51. The microstructure of TC21 alloy after superplastic deformation is treated with triple heat treatment. The effect of heat treatment parameters on the microstructure of TC21 alloy after superplastic deformation is studied. The first heat treatment temperature affects the grain boundary 偽 phase in the final microstructure of TC21 alloy. With the increase of the first heat treatment temperature, the grain boundary 偽 phase increases, and the grain boundary 偽 phase is less precipitated when the first heat treatment temperature is near the transition point. The size of the secondary 偽 phase increases with the increase of the secondary heat treatment temperature or the decrease of the cooling rate, and the secondary 偽 phase is coarse with the increase of the third heat treatment temperature, and the size of the secondary 偽 phase increases with the increase of the secondary heat treatment temperature or the cooling rate. When the cooling rate is slow (furnace cooling, 偽 phase precipitates in the grain boundary and grain, the microstructure is coarse Weichenite structure, when the cooling rate is higher, the long acicular martensite 偽 'and metastable 尾 phase are obtained. After the third heat treatment, the metastable 尾 phase precipitated fine needle-like 偽 phase, which appeared to be net-shaped. 3) Triple heat treatment could make the microstructure of TC21 alloy superplastic deformation in 尾 -phase region or two-phase region obtain most of the net structure. However, after heat treatment, there will still be a part of grain boundary 偽 phase in the microstructure. In this paper, the optimum heat treatment process for improving the microstructure of TC21 alloy after superplastic deformation is as follows: (1) 940 ~ 970 鈩，

本文編號：1879567