Ti60钛合金相变动力学及组织演变研究

发布时间：2018-03-21 05:23

  本文选题：高温钛合金　切入点：组织演变　出处：《西北工业大学》2015年博士论文　论文类型：学位论文

【摘要】：Ti60钛合金是我国研制的具有自主知识产权的600°C高温钛合金,可用于制造高推重比航空发动机关键部件。Ti60钛合金通过一系列的热处理可以实现力学性能的综合匹配。为了优化合金热处理工艺,并考察服役条件下的组织稳定性,需要系统研究合金在热处理及服役过程中的组织演变规律,探讨相变机制。因此,本文采用热膨胀法,结合扫描电镜和透射电镜等表征手段研究了Ti60钛合金在固溶热处理过程、连续冷却过程、等温过程,以及长期热暴露过程中的组织演变规律。深入探讨了α相的形核长大机制,以及α'马氏体的等温分解机制。此外,通过分析α2相和硅化物两种纳米相的析出规律,研究了热暴露对材料力学性能的影响。论文的主要研究内容和结果包括:(1)固溶温度与Ti60钛合金组织中α相体积分数近似呈线性关系,α相中Al元素含量随固溶温度升高而增加。固溶过程中过饱和的α相发生α→β转变,当固溶温度超过1020°C时,α片层不仅宽度减小,长轴末端也发生溶解并分裂成短片层。(2)合金自β相区以淬火或空冷条件冷却,组织发生β→α'马氏体转变,而且在α'马氏体内形成位错、层错等缺陷。另外在炉冷条件下,组织发生α→α2有序化转变。在α+β相区固溶淬火组织中发现块状α'马氏体,它从α相边界向外延伸,其取向与α相一致,而化学成分与β转变组织接近,可通过提高固溶温度和缩短保温时间促进形成块状α'马氏体。(3)采用膨胀法研究了合金连续冷却至室温过程的相变动力学。结果表明:当冷速超过50°C?s-1时,合金组织发生β→α'马氏体转变,马氏体转变温度(Ms)约为900°C;在20°C?s-1~5°C?s-1范围内,组织中部分β相在940°C~920°C范围内发生β→α转变,α相优先在晶界形核并长大,剩余的过饱和β相发生β→α'转变;当冷速降至3°C?s-1时,组织中全部β相发生β→α转变,α片层在晶界和晶内同时形核长大;冷速降至1°C?s-1时,α片层仅在晶界形核长大。本文基于上述结果建立了合金的连续冷却转变(CCT)图。(4)采用膨胀法研究了β→α等温相变动力学。基于JMA模型描述了等温过程中α相的形核长大机制。在1030°C保温时,α相仅在晶界形核并沿晶界延伸,对应Avrami指数n可近似为1.0;在950°C时n值增加至1.31,对应α相从晶界向晶内以片层形式生长。(5)α'马氏体组织在等温处理过程中发生α'→α+β转变,α相形核的同时伴随β相析出,最终形成细密的片层组织。随着等温温度降低,片层组织得到进一步细化。由此可知,利用等温过程中α'马氏体的分解机制,可实现组织细化。(6)Ti60钛合金在650°C、600°C或550°C长期热暴露后,组织中残余β相分解,并引起部分α相合并。另外,α相发生α→α2有序化转变,形成弥散分布的纳米尺寸颗粒。在550°C热暴露时,硅化物仅在α边界沉淀析出,最终成长为椭球形的S2型硅化物,长轴可达150nm;在650°C热暴露时,硅化物在α相边界和内部的位错和层错处大量析出,纳米相的析出会导致合金脆化,使得合金的室温延伸率低于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╁害鍜岀缉鐭�淇濇俯鏃堕棿淇冭繘褰㈡垚鍧楃姸危�

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