本文選題：高溫鈦合金　切入點(diǎn)：組織演變　出處：《西北工業(yè)大學(xué)》2015年博士論文　論文類型：學(xué)位論文

【摘要】：Ti60鈦合金是我國研制的具有自主知識(shí)產(chǎn)權(quán)的600°C高溫鈦合金,可用于制造高推重比航空發(fā)動(dòng)機(jī)關(guān)鍵部件。Ti60鈦合金通過一系列的熱處理可以實(shí)現(xiàn)力學(xué)性能的綜合匹配。為了優(yōu)化合金熱處理工藝,并考察服役條件下的組織穩(wěn)定性,需要系統(tǒng)研究合金在熱處理及服役過程中的組織演變規(guī)律,探討相變機(jī)制。因此,本文采用熱膨脹法,結(jié)合掃描電鏡和透射電鏡等表征手段研究了Ti60鈦合金在固溶熱處理過程、連續(xù)冷卻過程、等溫過程,以及長(zhǎng)期熱暴露過程中的組織演變規(guī)律。深入探討了α相的形核長(zhǎng)大機(jī)制,以及α'馬氏體的等溫分解機(jī)制。此外,通過分析α2相和硅化物兩種納米相的析出規(guī)律,研究了熱暴露對(duì)材料力學(xué)性能的影響。論文的主要研究?jī)?nèi)容和結(jié)果包括:(1)固溶溫度與Ti60鈦合金組織中α相體積分?jǐn)?shù)近似呈線性關(guān)系,α相中Al元素含量隨固溶溫度升高而增加。固溶過程中過飽和的α相發(fā)生α→β轉(zhuǎn)變,當(dāng)固溶溫度超過1020°C時(shí),α片層不僅寬度減小,長(zhǎng)軸末端也發(fā)生溶解并分裂成短片層。(2)合金自β相區(qū)以淬火或空冷條件冷卻,組織發(fā)生β→α'馬氏體轉(zhuǎn)變,而且在α'馬氏體內(nèi)形成位錯(cuò)、層錯(cuò)等缺陷。另外在爐冷條件下,組織發(fā)生α→α2有序化轉(zhuǎn)變。在α+β相區(qū)固溶淬火組織中發(fā)現(xiàn)塊狀α'馬氏體,它從α相邊界向外延伸,其取向與α相一致,而化學(xué)成分與β轉(zhuǎn)變組織接近,可通過提高固溶溫度和縮短保溫時(shí)間促進(jìn)形成塊狀α'馬氏體。(3)采用膨脹法研究了合金連續(xù)冷卻至室溫過程的相變動(dòng)力學(xué)。結(jié)果表明:當(dāng)冷速超過50°C?s-1時(shí),合金組織發(fā)生β→α'馬氏體轉(zhuǎn)變,馬氏體轉(zhuǎn)變溫度(Ms)約為900°C;在20°C?s-1~5°C?s-1范圍內(nèi),組織中部分β相在940°C~920°C范圍內(nèi)發(fā)生β→α轉(zhuǎn)變,α相優(yōu)先在晶界形核并長(zhǎng)大,剩余的過飽和β相發(fā)生β→α'轉(zhuǎn)變;當(dāng)冷速降至3°C?s-1時(shí),組織中全部β相發(fā)生β→α轉(zhuǎn)變,α片層在晶界和晶內(nèi)同時(shí)形核長(zhǎng)大;冷速降至1°C?s-1時(shí),α片層僅在晶界形核長(zhǎng)大。本文基于上述結(jié)果建立了合金的連續(xù)冷卻轉(zhuǎn)變(CCT)圖。(4)采用膨脹法研究了β→α等溫相變動(dòng)力學(xué)�；贘MA模型描述了等溫過程中α相的形核長(zhǎng)大機(jī)制。在1030°C保溫時(shí),α相僅在晶界形核并沿晶界延伸,對(duì)應(yīng)Avrami指數(shù)n可近似為1.0;在950°C時(shí)n值增加至1.31,對(duì)應(yīng)α相從晶界向晶內(nèi)以片層形式生長(zhǎng)。(5)α'馬氏體組織在等溫處理過程中發(fā)生α'→α+β轉(zhuǎn)變,α相形核的同時(shí)伴隨β相析出,最終形成細(xì)密的片層組織。隨著等溫溫度降低,片層組織得到進(jìn)一步細(xì)化。由此可知,利用等溫過程中α'馬氏體的分解機(jī)制,可實(shí)現(xiàn)組織細(xì)化。(6)Ti60鈦合金在650°C、600°C或550°C長(zhǎng)期熱暴露后,組織中殘余β相分解,并引起部分α相合并。另外,α相發(fā)生α→α2有序化轉(zhuǎn)變,形成彌散分布的納米尺寸顆粒。在550°C熱暴露時(shí),硅化物僅在α邊界沉淀析出,最終成長(zhǎng)為橢球形的S2型硅化物,長(zhǎng)軸可達(dá)150nm;在650°C熱暴露時(shí),硅化物在α相邊界和內(nèi)部的位錯(cuò)和層錯(cuò)處大量析出,納米相的析出會(huì)導(dǎo)致合金脆化,使得合金的室溫延伸率低于5%。
[Abstract]:Ti60 titanium alloy is 600 C high temperature titanium alloy developed in China with independent intellectual property rights, can be used in the manufacture of high thrust weight ratio aero-engine components of.Ti60 titanium alloy by heat treatment, can achieve a series of comprehensive mechanical properties. In order to optimize the treatment process, and investigate the stability of structure under service conditions, evolution needs to study the system alloy in heat treatment and service process of the organization, to explore the mechanism of phase transformation. Therefore, the thermal expansion method of Ti60 titanium alloy during the solution heat treatment process combined with scanning electron microscopy and transmission electron microscopy methods, continuous cooling and isothermal process, as well as long-term exposure to heat evolution in the process of organization after discussing the alpha phase nucleation and growth mechanism of isothermal martensite and alpha 'decomposition mechanism. In addition, through the analysis of alpha 2 and two nanometer silicide phase analysis law, Study on the effect of thermal exposure on the mechanical properties of materials. The main research contents and results include: (1) solid solution is a linear relationship between the alpha phase volume fraction and approximate temperature of Ti60 titanium alloy in a phase Al content increases with the increase of solution temperature. Solid solution of alpha to beta shift and satiety the alpha phase in the process, when the solution temperature exceeds 1020 C, alpha layer not only reduced width, long axis end also was dissolved and split into short layer. (2) since the beta phase in alloy quenching or air cooling cooling conditions, organization change, alpha beta 'martensite, and the formation of dislocations in the alpha' horse's body, stacking faults. In addition to the furnace cooling conditions, organization, alpha alpha 2. Alpha 'bulk ordering transformation of martensite was found in alpha + beta phase solid solution quenched, it extends outward from the alpha phase boundary, consistent with its orientation and alpha, and chemical composition with the transformed beta tissue close by 鎻愰珮鍥烘憾娓╁害鍜岀緝鐭繚娓╂椂闂翠績(jī)榪涘艦鎴愬潡鐘段，

本文編號(hào)：1642431