【摘要】：鈦鋁合金因?yàn)榫哂忻芏鹊?高溫強(qiáng)度高,抗蠕變和抗氧化能力強(qiáng)等特點(diǎn),一直是航天和汽車行業(yè)應(yīng)用材料研究的熱門,但低延展率和較差的成型性能阻礙了其在工程上的進(jìn)一步應(yīng)用。粉末冶金等技術(shù)的引入很有效地解決成形難題,特別對于復(fù)雜制件近終成形,可以消除宏觀偏析,對組織細(xì)化起到有效作用,而鈦鋁合金主要使用元素粉末法和預(yù)合金粉末法這兩種方法。元素粉末法的特點(diǎn)是原料的成本較低(如HDH粉等),但不適用于熱加工成形。預(yù)合金粉末法可以有效提高胚料的純凈度防止合金氧化,使合金具有高溫超塑性。隨著技術(shù)不斷革新氬氣霧化是制取高質(zhì)量鈦鋁預(yù)合金粉末比較成熟的工藝,可以使粉末有較好的球形度,具有明顯的快冷組織特征。在氣霧化過程中,熔融液體被高速的氣流打碎成極多較小的球形液滴,液滴在強(qiáng)對流作用下急劇冷卻。盡管如此利用粉末冶金的方法制備的鈦鋁合金仍然存在微觀缺陷,對成型后的材料的力學(xué)性能產(chǎn)生影響,研究表明熱加工可以改善材料的組織分布,甚至提高材料的力學(xué)性能,所以有必要對粉末冶金鈦鋁合金熱變形行為進(jìn)行更深入的研究。目前的研究多集中在鑄態(tài)鈦鋁合金粉末方面,而對鈦鋁合金預(yù)合金粉末方面的報道較少,尤其氬氣霧化制備的預(yù)合金粉末研究幾乎空白。由于制備工藝的不同胚料的組織性能也會有很大差異,因此對鈦鋁粉末合金熱變形行為研究十分重要。本文基于氬氣霧化預(yù)合金Ti-47.5Al-2Cr-2Nb-0.2W-0.2B合金粉末熱等靜壓后的坯錠制成圓柱狀試樣,尺寸為φ8mm×12 mm,然后經(jīng)過加工將兩個表面打磨拋光至平整。在熱力模擬實(shí)驗(yàn)機(jī)上進(jìn)行熱壓縮模擬實(shí)驗(yàn),探究該Ti-47.5Al合金高溫變形行為,建立Ti-47.5Al-2Cr-2Nb-0.2W-0.2B合金本構(gòu)方程,計算出激活能Q=~365.6 k J/mol,該方程的擬合相關(guān)系數(shù)和誤差分別為0.98922和3.30415%,預(yù)測與實(shí)驗(yàn)結(jié)果一致性較好。結(jié)合形變組織研究觀察了合金在1050-1200℃、應(yīng)變速率0.001-0.5s-1粉末冶金Ti-47.5Al合金的組織變化,采用SEM,EBSD和TEM對熱變形合金的微觀組織演變進(jìn)行了分析,發(fā)現(xiàn)材料中出現(xiàn)了細(xì)小的再結(jié)晶組織,并有層片結(jié)構(gòu)留在變形組織中。同時,基于Prasad失穩(wěn)準(zhǔn)則以及動態(tài)DMM模型,最終建立了該合金變形過程中的加工圖。基于所構(gòu)造的加工圖,該合金的最佳熱加工窗口是在1080-1180℃的溫度范圍和0.001-0.1s-1的低應(yīng)變速率。該研究中獲得的結(jié)果為高溫TiAl基合金零件的熱加工及生產(chǎn)提供理論依據(jù),為Ti-47.5Al合金熱加工工藝起到指導(dǎo)作用。
[Abstract]:Because of its low density, high temperature strength, high creep resistance and oxidation resistance, Ti-Al alloy has been a hot research field in aerospace and automotive industry. However, low ductility and poor molding properties hinder its further application in engineering. The introduction of powder metallurgy and other technologies can effectively solve the forming problems, especially for the near-final forming of complex parts, which can eliminate macro-segregation and play an effective role in microstructure refinement. Titanium-aluminum alloy mainly uses two methods: elemental powder method and pre-alloyed powder method. Element powder method is characterized by low cost of raw materials (such as HDH powder, etc.), but is not suitable for hot-working forming. The pre-alloy powder method can effectively improve the purity of the embryo to prevent the oxidation of the alloy and make the alloy have high temperature superplasticity. Argon atomization is a mature process for producing high-quality titanium-aluminum prealloyed powder, which can make the powder have a better sphericity and have obvious fast-cooling microstructure characteristics. In the process of gas atomization, the molten liquid is broken into many smaller spherical droplets by high-speed airflow, and the droplets are cooled sharply under the action of strong convection. However, the Ti-Al alloy prepared by powder metallurgy still has micro-defects, which has influence on the mechanical properties of the molded materials. The research shows that hot-working can improve the microstructure distribution of the materials and even improve the mechanical properties of the materials. Therefore, it is necessary to study the hot deformation behavior of P / M Ti-Al alloy. Most of the researches are focused on as-cast Ti-Al alloy powders, but few reports have been reported on Ti-Al alloy pre-alloy powders, especially the study of pre-alloy powders prepared by argon atomization is almost blank. It is very important to study the hot deformation behavior of Ti-Al powder alloy because the microstructure and properties of different embryo materials are different. Based on the ingot of argon atomized pre-alloyed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy powder after hot isostatic pressing, a cylindrical sample was made. The size is 蠁 8mm 脳 12 mm, and the two surfaces are polished to level after machining. The high temperature deformation behavior of Ti-47.5Al alloy was investigated by means of thermal compression simulation experiment on a thermal simulation machine. The constitutive equation of Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy was established and the activation energy Q, 365.6 kJ / mol, was calculated. The fitting correlation coefficient and error of the equation are 0.98922 and 3.30415%, respectively. The prediction is in good agreement with the experimental results. The microstructure change of 0.001-0.5s-1 powder metallurgy Ti-47.5Al alloy at 1 050 鈩，

本文編號：2452349