本文選題：Ti-6246合金 + 顯微組織��； 參考：《中國科學(xué)技術(shù)大學(xué)》2017年博士論文

【摘要】：Ti-6246合金是一種高強(qiáng)高溫鈦合金,常用在燃?xì)鉁u輪發(fā)動機(jī)的中溫部位,其長時(shí)使用溫度400℃左右,短期工作溫度可達(dá)540℃,在該溫度范圍內(nèi)具有優(yōu)異的力學(xué)性能。本文以Ti-6246合金為實(shí)驗(yàn)材料,利用金相顯微鏡、掃描電鏡、透射電鏡、X射線衍射儀等測試技術(shù),研究了熱加工、熱處理及焊接對合金顯微組織和力學(xué)性能的影響,為其進(jìn)一步應(yīng)用提供依據(jù)。應(yīng)用加工圖理論研究了Ti-6246合金的高溫變形行為和不同應(yīng)變條件下的變形機(jī)制。Ti-6246合金真應(yīng)力-真應(yīng)變曲線受加工硬化和動態(tài)軟化的雙重作用影響。在熱壓縮過程中,流變應(yīng)力峰值與溫度和應(yīng)變速率有關(guān)。流變應(yīng)力隨變形溫度的升高而降低,隨應(yīng)變速率的增加而增大。應(yīng)用Zener-Hollomon關(guān)系式以及雙曲正弦函數(shù)關(guān)系式,計(jì)算合金α+β兩相區(qū)的熱變形激活能為429.9 kJ·mol-1,β單相區(qū)的熱變形激活能為245.6 kJ·mol-1;建立了合金的高溫變形本構(gòu)方程,根據(jù)動態(tài)材料模型建立了合金的熱加工圖。通過對加工圖進(jìn)行分析可知,合金在895℃/0.5 s-1條件下發(fā)生動態(tài)再結(jié)晶,在動態(tài)再結(jié)晶區(qū)域內(nèi)熱變形后組織細(xì)小均勻。該合金的功率耗散效率的峰值區(qū)溫度為860℃,ε=0.001 s-1。在此區(qū)間內(nèi)合金發(fā)生動態(tài)回復(fù)與動態(tài)再結(jié)晶。在低溫高應(yīng)變速率區(qū),合金發(fā)生失穩(wěn)現(xiàn)象,其失穩(wěn)形式為流變局域化。熱處理工藝會顯著影響Ti-6246合金的顯微組織及力學(xué)性能,因此研究了固溶溫度和冷卻方式對合金的顯微組織、相組成和室溫拉伸變形行為的影響。在實(shí)驗(yàn)溫度范圍內(nèi),固溶處理后合金的相組成主要與冷卻方式相關(guān),在β單相區(qū)及(α+β)兩相區(qū)固溶后水冷,β相均轉(zhuǎn)化為α"馬氏體和少量亞穩(wěn)β相�？绽浣M織中β相轉(zhuǎn)變?yōu)楹猩倭康拇紊料嗟摩罗D(zhuǎn)變組織,且隨熱處理溫度的升高次生α相的含量增加,尺寸也逐漸增大。時(shí)效后組織中的亞穩(wěn)相發(fā)生分解,生成細(xì)小的次生α相。固溶后水冷試樣的拉伸曲線上出現(xiàn)"雙屈服"現(xiàn)象,并且隨固溶溫度的升高合金第一屈服點(diǎn)逐漸升高。水冷和空冷試樣經(jīng)595℃/8h時(shí)效后,合金的強(qiáng)度提高,塑形降低。這種趨勢在水冷試樣中更明顯。在兩相區(qū)空冷,合金對熱處理溫度不太敏感,經(jīng)595℃時(shí)效處理后合金室溫拉伸性能可達(dá)到較好的強(qiáng)塑性匹配。Ti-6246電子束焊接接頭由熔合區(qū)、熱影響區(qū)和母材區(qū)三個(gè)區(qū)域組成,分析表明熔合區(qū)中由α相和β相組成,無α"馬氏體和亞穩(wěn)β相出現(xiàn)。焊接接頭顯微硬度呈不均勻分布,焊接接頭各區(qū)域隨距熔合區(qū)中心距離減少,顯微硬度逐漸增加。焊后熱處理后,熔合區(qū)和熱影響區(qū)顯微組織中析出細(xì)小的次生α相片層。隨著焊后熱處理溫度由545℃增加至645℃,片層的厚度增大,數(shù)量逐漸增加。焊接接頭熔合區(qū)和熱影響區(qū)中的顯微硬度值先升高再降低。焊接接頭室溫拉伸斷裂均發(fā)生在母材區(qū)。焊接接頭斷口可觀察到以韌窩為主的塑性斷裂。焊后熱處理會影響焊接接頭熔合區(qū)、熱影響區(qū)和母材區(qū)中α相的尺寸和形狀,進(jìn)而影響焊接接頭的拉伸性能。焊后熱處理?xiàng)l件下,接頭拉伸強(qiáng)度的降低歸因于母材中α相片層粗化導(dǎo)致的強(qiáng)度降低,接頭拉伸塑性的改善歸因于焊接接頭各區(qū)域拉伸塑性的提高。Ti-624x合金焊接接頭各區(qū)域的顯微組織隨Mo含量的變化而改變。Mo含量越低,Ti-624x合金焊縫熔合區(qū)中β柱狀晶晶粒尺寸越大。熔合區(qū)柱狀晶內(nèi)部為全片層組織,且隨著合金Mo含量的增加,柱狀晶內(nèi)部α相的尺寸逐漸降低。熱影響區(qū)的組織由大量的等軸狀β晶粒組成,且晶粒的尺寸隨著與熔合區(qū)中心線距離的增大而減小。熱影響區(qū)的顯微組織為介于母材及熔合區(qū)之間的過渡組織,隨著與熔合區(qū)中心線距離的減小逐漸由雙態(tài)組織過渡到片層組織。焊接接頭不同區(qū)域次生α相分布不同,導(dǎo)致焊態(tài)焊接接頭的顯微硬度呈不均勻分布。且隨Mo含量的增加,焊接接頭的硬度逐漸升高,其中Mo元素含量在4-5時(shí)硬度值的變化最大。隨Mo含量的增加,熔合區(qū)的強(qiáng)度逐漸提高,室溫塑性逐漸減低。
[Abstract]:Ti-6246 alloy is a high strength and high temperature titanium alloy, which is usually used in the medium temperature part of a gas turbine engine. It is used at a temperature of about 400 C for a long time, the short-term working temperature is up to 540 degrees C, and it has excellent mechanical properties in the range of temperature. This paper takes Ti-6246 alloy as the experimental material, and uses metallographic microscope, scanning electron microscope, transmission electron microscope, X ray. The influence of heat processing, heat treatment and welding on Microstructure and mechanical properties of alloy is studied by the diffraction instrument and other testing techniques, which provide the basis for its further application. The high temperature deformation behavior of Ti-6246 alloy and the deformation mechanism of.Ti-6246 alloy under different strain conditions are studied by using the theory of processing drawing. In the process of thermal compression, the peak value of the rheological stress is related to the temperature and the strain rate. The rheological stress decreases with the increase of the deformation temperature and increases with the increase of the strain rate. The thermal deformation activation energy of the alloy alpha + beta two phase region is calculated by using the Zener-Hollomon relation and the hyperbolic sinusoidal function formula. For 429.9 kJ. Mol-1, the activation energy of thermal deformation of a single phase region is 245.6 kJ. Mol-1, the constitutive equation of high temperature deformation of the alloy is established. A hot working diagram of the alloy is set up according to the dynamic material model. By analyzing the working diagram, the alloy is recrystallized at 895 C /0.5 S-1 and after the thermal deformation in the dynamic recrystallization region. The peak region temperature of the power dissipation efficiency of the alloy is 860 degrees C, and the alloy has dynamic recovery and dynamic recrystallization in this zone. In the low temperature high strain rate region, the alloy is unstable, and its instability form is the rheological localization. The microstructure and force of the Ti-6246 alloy will be significantly affected by the heat treatment technology. The effect of solid solution temperature and cooling mode on the microstructure, phase composition and tensile deformation behavior of the alloy is studied. In the experimental temperature range, the phase composition of the alloy is mainly related to the cooling mode in the experimental temperature range, and the phase of the beta phase is transformed into a "martensite and a small amount of submartensite" in the phase region of the beta single phase and (alpha + beta) two phase. The beta phase is stable in the air cooled tissue, and the beta phase changes to a small amount of secondary alpha phase, and the secondary alpha phase increases with the increase of the heat treatment temperature. The metastable phase in the tissue is decomposed to produce a small secondary alpha phase. The "double yield" phenomenon appears on the tensile curves of the water-cooled specimens after solid solution. With the increase of the solid solution temperature, the first yield point of the alloy increases gradually. The strength of the alloy is increased and the shape of the alloy decreases after 595 /8h aging. This trend is more obvious in the water cooled sample. The alloy is not very sensitive to the heat treatment temperature in the two phase air cooling, and the tensile properties of the alloy at room temperature after 595 C are better than that of the alloy. The strong plastic matching.Ti-6246 electron beam welding joint consists of three regions of fusion zone, heat affected zone and parent material area. The analysis shows that the fusion zone is composed of alpha and beta phase, without alpha martensite and metastable beta phase. The microhardness of welded joint is uneven distribution, and the distance of the welding joint is reduced with the distance of the distance fusion zone, and the microhardness is the same. After heat treatment, the fine secondary alpha phase layer is precipitated in the microstructure of the fusion zone and the heat affected zone. With the increase of heat treatment temperature from 545 to 645 C after welding, the thickness of the lamellar layer increases, and the number of the microhardness in the weld joint and the heat affected zone increases first and then decreases. The welding joint is stretched at room temperature. The crack occurs at the parent material area. The fracture of the welded joint can be observed as the plastic fracture mainly in the dimple. The post weld heat treatment will affect the size and shape of the alpha phase in the weld joint, the heat affected zone and the parent material area, and then influence the tensile properties of the welded joint. The reduction of the tensile strength of the joint is attributed to the alpha phase in the parent material after the welding heat treatment. The strength of the lamellar coarsening is reduced. The improvement of the tensile plasticity of the joint is attributed to the increase of the tensile plasticity of the welded joints in various regions. The microstructure of the.Ti-624x alloy welded joint varies with the content of Mo, the lower the content of.Mo, the larger the grain size of the beta columnar crystal in the fusion zone of the Ti-624x alloy welds. With the increase of the Mo content of the alloy, the size of the internal alpha phase in the columnar crystal gradually decreases. The microstructure of the heat affected zone consists of a large number of equiaxed beta grains, and the size of the grain decreases with the increase of the distance between the central line of the fusion zone and the transition tissue between the parent material and the fusion zone. The decrease of the distance from the center line of the fusion zone gradually from the double state to the lamellar tissue. The distribution of the secondary alpha phase in the welded joint is different, which leads to the uneven distribution of the microhardness of the welded joint. The hardness of the welded joint is gradually increased with the increase of the content of Mo, and the change of the hardness value of the Mo element is the largest when the content of the element is 4-5. With the increase of Mo content, the strength of the fusion zone gradually increases and the room temperature plasticity gradually decreases.
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TG456.3

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1 王國強(qiáng);Ti-6246鈦合金熱機(jī)械處理及電子束焊接性研究[D];中國科學(xué)技術(shù)大學(xué);2017年

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本文編號：1929152