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

【摘要】：Ti60鈦合金是我國研制的具有自主知識產(chǎn)權的600°C高溫鈦合金,可用于制造高推重比航空發(fā)動機關鍵部件。Ti60鈦合金通過一系列的熱處理可以實現(xiàn)力學性能的綜合匹配。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,探討相變機制。因此,本文采用熱膨脹法,結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相的形核長大機制,以及α'馬氏體的等溫分解機制。此外,通過分析α2相和硅化物兩種納米相的析出規(guī)律,研究了熱暴露對材料力學性能的影響。論文的主要研究內(nèi)容和結果包括:(1)固溶溫度與Ti60鈦合金組織中α相體積分數(shù)近似呈線性關系,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轉變,當固溶溫度超過1020°C時,α片層不僅寬度減小,長軸末端也發(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'馬氏體轉變,而且在α'馬氏體內(nèi)形成位錯、層錯等缺陷。另外在爐冷條件下,組織發(fā)生α→α2有序化轉變。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,而化學成分與β轉變組織接近,可通過提高固溶溫度和縮短保溫時間促進形成塊狀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力學。結果表明:當冷速超過50°C?s-1時,合金組織發(fā)生β→α'馬氏體轉變,馬氏體轉變溫度(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轉變,α相優(yōu)先在晶界形核并長大,剩余的過飽和β相發(fā)生β→α'轉變;當冷速降至3°C?s-1時,組織中全部β相發(fā)生β→α轉變,α片層在晶界和晶內(nèi)同時形核長大;冷速降至1°C?s-1時,α片層僅在晶界形核長大。本文基于上述結果建立了合金的連續(xù)冷卻轉變(CCT)圖。(4)采用膨脹法研究了β→α等溫相變動力學。基于JMA模型描述了等溫過程中α相的形核長大機制。在1030°C保溫時,α相僅在晶界形核并沿晶界延伸,對應Avrami指數(shù)n可近似為1.0;在950°C時n值增加至1.31,對應α相從晶界向晶內(nèi)以片層形式生長。(5)α'馬氏體組織在等溫處理過程中發(fā)生α'→α+β轉變,α相形核的同時伴隨β相析出,最終形成細密的片層組織。隨著等溫溫度降低,片層組織得到進一步細化。由此可知,利用等溫過程中α'馬氏體的分解機制,可實現(xiàn)組織細化。(6)Ti60鈦合金在650°C、600°C或550°C長期熱暴露后,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有序化轉變,形成彌散分布的納米尺寸顆粒。在550°C熱暴露時,硅化物僅在α邊界沉淀析出,最終成長為橢球形的S2型硅化物,長軸可達150nm;在650°C熱暴露時,硅化物在α相邊界和內(nèi)部的位錯和層錯處大量析出,納米相的析出會導致合金脆化,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╂椂闂翠績榪涘艦鎴愬潡鐘段，

本文編號：1642431