本文關(guān)鍵詞： beta gamma TiAl合金 顯微組織 性能 高溫變形行為 鍛造　出處：《太原理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：TiAl合金密度低、強(qiáng)度高、抗氧化性能以及抗蠕變性能優(yōu)異,是航空航天及汽車工業(yè)領(lǐng)域非常有前景的一種輕質(zhì)高溫結(jié)構(gòu)材料。Beta gamma TiAl合金被證明具有良好的熱加工性能。本文采用非自耗真空電弧熔煉技術(shù)制備了Ti-44Al-(0,4Nb,4V,2Mo,4Mo)(at%)合金,研究了Nb,V,Mo對TiAl合金組織的影響;基于對V、Mo和Nb元素的分析,采用感應(yīng)凝殼熔煉技術(shù)制備了成分為Ti-44Al-4Nb-4V-0.3Mo-Y(at%)的beta gamma TiAl合金,并對其組織、性能、高溫變形行為以及鍛造工藝進(jìn)行了系統(tǒng)的研究。Nb、V、Mo這三種元素的β相穩(wěn)定能力為MoVNb,4at%的Nb沒有使合金形成穩(wěn)定的B2相,而添加4at%的V或2at%的Mo可在合金中有效保留B2相,B2相將粗大的片層團(tuán)分割成很多細(xì)小的片層團(tuán)。當(dāng)Mo的含量增加到4at%,合金形成了魏氏體組織。鑄態(tài)Ti-44Al-4Nb-4V-0.3Mo-Y合金為近片層組織,熱等靜壓和均勻化退火后成為近γ組織。在850℃高于該合金的韌脆轉(zhuǎn)變溫度,合金的斷后伸長率快速增加到13%。該合金抗氧化性能較好,800℃循環(huán)氧化80h后氧化增重量只有1.92 mg/cm2。在β+γ兩相區(qū)熱處理時,α相同時遵循與γ相的Blackburn位向關(guān)系以及與β相的Burgers位向關(guān)系從β/B2晶粒中析出,得到粗大的近片層組織。在α+β+γ三相區(qū)進(jìn)行熱處理分別可以得到細(xì)小的近γ組織,雙態(tài)組織和近片層組織。在α+β兩相區(qū)進(jìn)行熱處理可以完全消除β相獲得全片層組織。采用等溫壓縮熱模擬實(shí)驗(yàn)研究了Ti-44Al-4Nb-4V-0.3Mo-Y合金的高溫變形行為和組織演變規(guī)律。該合金變形抗力較小,熱加工性能良好,但在TiAl合金的服役溫度下仍能保持較高的強(qiáng)度。通過熱力模擬數(shù)據(jù)計(jì)算出了該合金的熱變形激活能,并建立了高溫變形本構(gòu)方程。該合金主要有兩種典型的變形組織,在應(yīng)變速率為0.01s-1時,合金動態(tài)再結(jié)晶比較充分。采用不同工藝對Ti-44Al-4Nb-4V-0.3Mo-Y合金進(jìn)行了鍛造。鍛造工藝為1250℃/0.02 s-1時獲得了尺寸約20μm的細(xì)小等軸近片層組織,并且鍛態(tài)合金的室溫拉伸性能得到顯著提高,斷后伸長率和抗拉強(qiáng)度分別達(dá)到了1.9%和842MPa。鍛造工藝為1200℃/0.02s-1或采用降溫鍛造時可以得到晶粒尺寸非常細(xì)小的γ和B2混合組織,但鍛態(tài)合金的室溫拉伸性能依然較差。B2相可以阻礙裂紋的擴(kuò)展,但近片層組織的斷裂韌性高于細(xì)小的γ和B2混合組織的斷裂韌性。
[Abstract]:TiAl alloy has low density, high strength, excellent oxidation resistance and creep resistance. Beta gamma TiAl alloy is a promising material in aerospace and automotive industry. It has been proved that it has good hot working properties. Ti-44Al-0NbC4NbC4NbC4V2MoO4MoTZ) alloy has been prepared by non-consumable vacuum arc melting technique in this paper. Based on the analysis of the elements of TiAl, Ti-44Al-4Nb-4V-0.3Mo-Yatai (Ti-44Al-4Nb-4V-0.3Mo-Yathe) beta gamma TiAl alloy was prepared by means of inductive shell melting technique, and the microstructure and properties of the alloy were also studied, and the microstructure and properties of Ti-44Al-4Nb-4V-0.3Mo-Yatai alloy were investigated. The deformation behavior at high temperature and forging process were studied systematically. The 尾 -phase stability of the three elements, I. e., MoVNbC4at% NB, did not make the alloy form a stable B2 phase. However, the addition of 4at% V or 2at% Mo can effectively retain B2 phase B 2 phase in the alloy and divide the coarse lamellar clusters into many small lamellar clusters. When Mo content increases to 4 att, the alloy forms Weiss structure, and the as-cast Ti-44Al-4Nb-4V-0.3Mo-Y alloy is near lamellar structure. After annealing under hot isostatic pressure and homogenization, the microstructure of the alloy is near 緯, which is higher than the ductile-brittle transition temperature of the alloy at 850 鈩，

本文編號：1532222