SiC纤维增强钛基复合材料的拉曼光谱研究

发布时间：2018-01-08 15:39

本文关键词：SiC纤维增强钛基复合材料的拉曼光谱研究　出处：《西北工业大学》2015年博士论文　论文类型：学位论文

【摘要】：CVD SiC纤维增强钛基复合材料具有高比强度、比刚度、在较高温度条件下组织结构稳定等优点,因此受到航空界的广泛关注,被认为是一种应用前景良好的耐高温结构材料。由于SiC纤维和钛合金基体在高温环境下为非化学平衡体系,因此纤维和基体合金之间的高温化学反应以及复合材料各部分在高温下的组织演变将不可避免,这会影响复合材料在该温度环境下的性能演变以及使用寿命。传统的SiC纤维组织研究方法主要为透射电镜,研究内容多为晶粒尺寸测量和晶体缺陷的观测。复合材料界面反应产物的鉴定主要依靠透射电镜观测和电子衍射分析。由于透射电镜分析对制样要求较高,因此效率较低无法用于指导复合材料制备工艺的改进。在相关报道中,拉曼光谱也被少量用于SiC纤维的组织的定性表征。同时,常见的SiC纤维增强钛基复合材料的界面反应产物均具备拉曼活性。另外,拉曼光谱技术具有对制样要求很低,对试样无损伤,测试效率高的优点。因此,本研究使用拉曼光谱对SiC纤维及其复合材料界面反应产物的组织及高温热暴露导致的组织演变进行了试验性表征。同时通过透射电镜、扫描电镜和能谱的结果辅助并验证拉曼表征结果的正确性。对钨芯SiC纤维组织的透射电镜的研究表明,其W-SiC界面反应产物依次为W/W_2C/W_5Si_3/SiC。这种产物排布主要由SiC高温沉积过程中CH_3SiCl_3分解产物和后续扩散反应导致。纤维的SiC部分晶粒尺寸从内向外沿径向出现先增大后减小的规律。另外SiC晶粒中存在高密度层错孪晶等缺陷,而且分布没有规律。拉曼光谱沿纤维径向线扫的分析结果与透射电镜的观测结论表明SiC TO峰信息可用于SiC晶粒的尺寸和缺陷的表征。拉曼光谱仪同时检测到SiC纤维部分区域存在Si的共沉积,以及由此导致的畸变和残余应力。对不同温度热暴露的纤维进行拉曼光谱研究显示,沿纤维径向不同区域的SiC组织高温稳定性不同。研究发现使用C_3H_8+C_2H_2+H_2等比例混合作为反应气体在900℃裂解并分两次沉积得到的双层热解碳涂层厚度稳定(3μm左右),可以用于连续生产。这种双层碳涂层在拉伸过程中易于在涂层之间发生脱粘,有利于复合材料加载过程中的纤维拔出,可以有效提高复合材料的断裂韧性和疲劳寿命。拉曼光谱和透射电镜的分析表明C_3H_8+C_2H_2+H_2和C_2H_2+H_2制备的碳涂层组织非常相似。通过碳涂层拉曼光谱中的D峰与G峰比值测算出的热解碳纳米晶尺寸接近透射电镜观测结果。同时拉曼光谱的研究表明,这种热解碳的组织可以在低于900℃的高温下保持稳定。对SiCf/C/Mo/Ti_6Al4V复合材料的界面反应产物的拉曼光谱研究表明,700-800℃200小时热暴露后,界面反应产物为TiCx,同时有游离碳存在。900℃200小时热暴露后,界面反应产物的排列顺序为SiC/Ti_5Si_3/TiCx/Ti_6Al_4V,这与透射电镜的主要分析结论一致。然而,透射电镜研究还发现SiC与Ti5Si3层之间还存在较薄Ti_3SiC_2层。错过Ti_3SiC_2层是由于Ti_5Si_3和Ti_3SiC_2拉曼谱线的相似性以及光谱仪分辨率的限制。另外800-900℃200小时热暴露后,Mo和C原子在复合材料基体中的扩散导致碳化物颗粒生成。经过拉曼光谱和透射电镜的分析,确定颗粒分为Ti_3Al C_2和TiCx两类。同时颗粒中存在结构缺陷,而且Ti_3AlC_2的生成与周边生成的TiC_x密切相关。拉曼光谱对制备态SiC_f/Ti43Al9V复合材料的界面反应产物的分析结果为SiC_f/TiC_x/Ti_2AlC/Ti43Al9V与透射电镜分析结果一致。高分辨透射电镜观察发现反应层TiC_x晶粒中存在大量层错孪晶等缺陷,这可能是导致TiC_x激发出拉曼信号的原因。Ti_2AlC的拉曼特征峰出现的不同程度展宽,是由于晶粒中存在组织缺陷。对800-900℃200小时热暴露试样的拉曼分析表明,随着热暴露温度升高,界面反应产物逐渐向Ti_2AlC转变。
[Abstract]:CVD SiC fiber reinforced titanium matrix composites with high strength, stiffness, organizational advantages of stable structure in high temperature conditions, so it is widely concerned by the aviation industry, is considered to be resistant to high temperature structural materials a good application prospect. Because of the SiC fiber and titanium alloys for chemical non-equilibrium system at high temperature under the environment of high temperature, so the chemical reaction between fiber and matrix alloy as well as each part of composite structure under high temperature evolution will be inevitable, it will affect the performance of composite materials in the temperature evolution and life. The traditional research method of SiC fiber is the main research content for the TEM observation of grain size measurement and the crystal defects. Identification of interfacial reaction products mainly rely on the analysis of transmission electron microscopy and electron diffraction. The TEM analysis of sample preparation High efficiency is low, therefore cannot be used to guide the improvement of preparation process of composites. In the relevant reports, a small amount of Raman spectra were also used to qualitatively characterize the SiC fiber organization. At the same time, the common SiC fiber reinforced interfacial reaction of titanium matrix composites have the Raman activity. In addition, Raman spectroscopy is a requirement for sample preparation is very low, no damage to the sample, has the advantages of high testing efficiency. Therefore, this study uses heat and high temperature Raman spectra of reaction products and composites SiC fiber exposure resulted in the evolution of organization through the experimental characterization. At the same time correctness by transmission electron microscopy, scanning electron microscopy and energy spectrum and auxiliary results to verify the results of characterization. Raman TEM research on tungsten core SiC fiber tissue showed that the W-SiC interfacial reaction products were W/W_2C/W_5Si_3/SiC. this product is mainly composed of SiC high temperature. Result CH_3SiCl_3 decomposition and subsequent diffusion during the deposition reaction. Fiber SiC part of the grain size from the inside to the outside along the radial direction appears increased first and then decreased. The presence of a high density of stacking fault defects also in SiC grains, and the irregular distribution. Observation results of the Raman spectrum along the fiber radial line scanning and transmission electron microscopy the SiC showed that the TO peak information can characterize the grain size of SiC and defects. At the same time for Raman spectroscopy detection of SiC fiber part co deposition process of Si, and the resulting distortion and residual stress of different temperature. The heat exposure of the fiber Raman spectra showed that different tissues along the SiC fiber radial temperature stability in different areas. The study found that the double pyrolytic carbon coating using C_3H_8+C_2H_2+H_2 mixture as reaction gas at 900 DEG C and two pyrolysis deposition thickness The degree of stability (about 3 m), can be used for continuous production. This double carbon coating is easy to occur in the coating debonding during the stretching process, a composite fiber pull to the loading process, can effectively improve the fracture toughness and fatigue life of composite materials. Analysis of Raman spectra and TEM showed that the carbon coating C_3H_8+C_2H_2+H_2 and C_2H_2+H_2 are very similar. The preparation of carbon coating in the Raman spectra of D peak and G peak ratio estimates of the pyrolytic carbon nanocrystal size close to the results observed by transmission electron microscopy. The Raman spectroscopic studies showed that this kind of pyrolytic carbon organization can remain stable at high temperature lower than 900 DEG C. Raman spectroscopy the interfacial reaction of SiCf/C/Mo/Ti_6Al4V composites showed that 700-800 DEG C for 200 hours after thermal exposure, the interfacial reaction product is TiCx, while the free carbon.900 DEG C for 200 hours hot storm Lucy, interfacial reaction products in the order of SiC/Ti_5Si_3/TiCx/Ti_6Al_4V, the main analysis and TEM consistent conclusion. However, TEM study also found that between SiC and Ti5Si3 layer there is a thin layer of Ti_3SiC_2. Miss Ti_3SiC_2 layer is due to the similarity and limit the resolution of Ti_5Si_3 and Ti_3SiC_2 spectroscopy Raman spectra. The other 800-900 DEG C 200 hours after thermal exposure, diffusion of Mo and C atoms in the composite matrix of lead carbide particles generated. Through the analysis of Raman spectroscopy and transmission electron microscopy, determination of the particle is divided into Ti_3Al C_2 and TiCx two. At the same time, the presence of structural defects and the formation of Ti_3AlC_2 particles, and the surrounding TiC_x generated by the interfacial reaction are closely related. Raman spectra of deposited SiC_f/Ti43Al9V composites on the analysis results for SiC_f/TiC_x/Ti_2AlC/Ti43Al9V and TEM analysis results are consistent. Resolution transmission electron microscopy showed the existence of a large number of stacking fault defects reaction layer in TiC_x grains, this may be the cause of TiC_x excitation in different degrees of broadening of Raman peaks of.Ti_2AlC Raman signal appears, is due to the presence of defects of 800-900 grains. Raman C 200 hours exposure to heat sample analysis shows that, with the heat exposure to elevated temperature, interfacial reaction products gradually transition to Ti_2AlC.

【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB333

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