本文關鍵詞： TiAl合金 熱變形行為 熱加工圖 包套軋制 氧化行為　出處：《北京科技大學》2016年博士論文　論文類型：學位論文

【摘要】：TiAl合金具有低密度、高強度、優(yōu)異的阻燃能力以及優(yōu)良的抗蠕變性能和抗疲勞性能等優(yōu)點,成為航空航天領域最具競爭力的輕質(zhì)結(jié)構材料之一。但TiAl合金熱變形能力差,室溫塑性低以及750℃以上的抗氧化性能不足等制約了該合金的實際工程化應用。本文通過添加p相穩(wěn)定元素(Nb和Mo)制備出高溫時含一定量具有BCC結(jié)構的p相TiAl合金,提高了其熱變形能力,同時改善了抗氧化性能。目前,有關添加Nb和Mo元素的含p/B2相TiAl合金的板材軋制及氧化行為方面的研究報道較少,也是該合金在工業(yè)試制過程中急需解決的關鍵性問題,對該合金最終實現(xiàn)商業(yè)化生產(chǎn)具有現(xiàn)實意義。本文對該合金的熱變形行為、板材制備和氧化行為系統(tǒng)地開展了相關基礎研究,主要工作和結(jié)果如下：(1)采用真空懸浮熔爐制備了尺寸為φ110mm × 190mm的Ti-44.45A1-3.80Nb-1.01Mo-0.29Si-0.14B合金(簡稱TNM合金)鑄錠。經(jīng)熱等靜壓和均勻化處理后的TNM合金無明顯成分偏析和微觀裂紋,組織由γ/α2片層團、β/B2相和γ相組成,并確立了該合金的凝固過程和相變規(guī)律。(2)通過Gleeble3500模擬壓縮鑄態(tài)TNM合金實驗證明含β/B2相的TNM合金具有較好的熱加工性,可在1200～1250℃及0.01～0.5s-1區(qū)內(nèi)進行變形,該合金屬負溫度敏感材料和正應變速率敏感材料,其流變應力曲線的升高、降低及平穩(wěn)過程對應了加工硬化和應變軟化的交替控制和動態(tài)平衡過程。利用摩擦修正后的熱壓縮實驗數(shù)據(jù)求解了不同應變條件下的材料常數(shù),構建了TNM合金的本構模型,并驗證了此模型能很好的預測該合金的熱變形流變規(guī)律。隨變形溫度升高和應變速率減小,TNM合金的動態(tài)再結(jié)晶的臨界應變減小。TNM合金低溫和高溫變形機制分別以Y相位錯滑移和β、α和γ相的位錯滑移為主,變形軟化機制為丫相的動態(tài)再結(jié)晶。在高溫變形過程中β相起到協(xié)調(diào)或“潤滑”作用,提高合金的變形能力。(3)基于動態(tài)材料模型(DMM),建立了鑄態(tài)TNM合金的熱加工圖,研究了在熱加工圖不同區(qū)域中材料組織的演變規(guī)律,按能量耗散效率η將熱加工圖分為安全區(qū)域和流變失穩(wěn)區(qū)域。從未經(jīng)鍛造TNM合金鑄錠上取料包套,成功地在加熱溫度為1250℃和道次軋制速度遞減(112/75/55mm/s)的條件下軋制出尺寸為510mm × 105mm×1.40mm的板材。軋態(tài)TNM合金的顯微組織為細小的近γ組織,通過熱處理其力學性能得到改善。(4)在TNM合金升溫階段的氧化過程,氧化物首先在γ相上生長,774℃是氧化物明顯迅速長大的開始溫度點。TNM合金在800℃的氧化實驗表明：等溫氧化500h后氧化膜保持完整,循環(huán)氧化710次時氧化膜開始剝落,而外加拉應力則提高了合金的氧化速率;該合金抗氧化性能明顯好于傳統(tǒng)的Ti-48Al-2Cr-2Nb合金。Nb和Mo的協(xié)同作用改變了合金的氧化膜形成機制,形成連續(xù)致密的A1203氧化膜,可阻礙氧原子向內(nèi)擴散降低了氧化速率,提高了TNM合金的長期抗氧化性。
[Abstract]:The TiAl alloy has low density, high strength, excellent flame retardant ability and excellent creep resistance and anti fatigue performance has become one of the most competitive lightweight structural materials in the aerospace industry. But the TiAl alloy hot deformation ability, ductility and low oxidation resistance of 750 DEG C for lack of practical constraints the engineering application of the alloy in this paper. By adding P elements (Nb and Mo) stable prepared at high temperature with a certain amount of BCC structure with P phase TiAl alloy, improve the deformation capacity of the heat, while improving the antioxidant properties. At present, with adding Nb and Mo elements with p/B2 phase TiAl alloy the Research Report of the rolling and oxidation behavior of less, and is also the key issue of the alloy in the industrial development process needs to be solved, the alloy eventually achieve commercial production. This paper has practical significance on the alloy heat The deformation behavior of sheet, preparation and oxidation system to carry out the basic research, the main work and results are as follows: (1) preparing the size of Ti-44.45A1-3.80Nb-1.01Mo-0.29Si-0.14B alloy with 110mm * 190mm vacuum furnace for suspension (TNM alloy) ingots. By hot isostatic pressing and homogenization obvious composition segregation and micro crack free TNM alloy treatment, organized by the gamma / alpha 2 lamellar, /B2 and beta gamma phase composition, and established the solidification process and the phase transformation of the alloy. (2) through the Gleeble3500 compression simulation of cast TNM alloys containing TNM experiments show that the B2 alloy has good thermal / beta processing, can be in 1200 to 1250 DEG C and 0.01 ~ 0.5s-1 in the area of deformation of this alloy is a negative temperature sensitive material and positive strain rate sensitive material, the rheological curves should be increased, and the lower stationary process corresponds to alternate work hardening and strain softening Control and dynamic balance process. Using friction modified hot compress test data for material constants under different strain condition, constructed the constitutive model of TNM alloy, and proves that the model can well predict the thermal deformation of the alloy rheological law. With the increase of deformation temperature and decreasing strain rate, critical strain the dynamic recrystallization of TNM alloy decreases.TNM alloy at low temperature and high temperature deformation mechanism with Y phase fault slip and beta, alpha and gamma phase dislocation slip and deformation softening mechanism for y phase dynamic recrystallization. During the process of high temperature deformation phase to coordinate or "lubricating" effect, improve the ability of deformation of alloy. (3) based on the dynamic material model (DMM), established the thermal processing map of TNM cast alloy, studied the microstructure evolution of materials in the hot processing map in different regions, according to the energy dissipation efficiency in the hot processing map can be divided into safety zone Domain and flow instability regions. Never forged TNM alloy ingot material package, successfully in the heating temperature is 1250 DEG C and rolling speed decreasing (112/75/55mm/s) under the condition of rolling plate size is 510mm * 105mm * 1.40mm. The microstructure of rolled TNM alloy is finer near gamma. Through heat treatment the mechanical properties were improved. (4) at the stage of heating and oxidation process of TNM alloy, oxide growth in the first phase, 774 C is obviously shows that the oxide grew rapidly start temperature of.TNM alloy in the oxidation experiments of 800 DEG C: 500h after isothermal oxidation film remains intact, 710 times of cyclic oxidation oxide film to start off, then increase the oxidation rate of stress and Gallas; synergistic effect of antioxidant properties of this alloy is obviously better than the traditional Ti-48Al-2Cr-2Nb alloy.Nb and Mo alloy changed the oxide film formation mechanism, shape As a continuous and compact A1203 oxide film, the oxidation rate of oxygen atoms can be hindered by the inward diffusion of oxygen atoms, and the long-term oxidation resistance of TNM alloy is improved.

【學位授予單位】：北京科技大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG146.2

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相關期刊論文 前1條

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本文編號：1444916