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高温抗氧化复合材料及其热防护涂层的制备与性能研究
Alternative TitleInvestigations on Preparation and Property of High Temperature Oxidation Resistance Ceramic Composit
骆丽杰
Subtype博士
Thesis Advisor张伟刚
2013-05-01
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
KeywordCf/c-sic-bn   铬酸钴(Ccr)   力学性能   抗氧化性能   热辐射性能   防护涂层
Abstract新型航空发动机的热端部位,特别是高温涡轮叶片、高温燃烧室、调节片等部位对材料的耐高温和抗氧化性能提出了更高的要求,在高温高压等苛刻应用环境下,需要寻求一种长寿命抗氧化的高温复合材料。具有低密度、高强度、高模量、低热膨胀系数和导热性好等一系列优异性能的碳纤维增强碳(C/C)复合材料是最具希望的候选材料之一,但它存在高温有氧环境下易被氧化和现有复合防护涂层技术可靠性差等问题,对C/C复合材料同时进行基体改性和表面涂层防护是提高其抗氧化性能的有效方法。本文基于SiC、BN具有优异的抗氧化性能,首先以前驱体转化法制备SiC/BN陶瓷,研究前驱体陶瓷转化的热解过程、陶瓷结构、性能及高温热稳定性能并分析其机理。在此基础上,以SiC/BN为基体制备抗氧化Cf/C–SiC–BN复合材料,研究制备工艺、基体组成等对材料力学性能和抗氧化性能的影响,对其氧化过程进行分析。同时还开展了热辐射防护涂层铬酸钴(CoCr2O4, CCR)材料的制备研究,研制了CCR涂层–Cf/C–SiC–BN新型复合材料,初步探索了整体复合材料的力学性能和抗氧化性能。主要研究内容和结论如下: (1) 利用聚碳硅烷(PCS)和自制的BN前驱体(PBN)的共溶–互熔特性,制备混合前驱体,并通过共热解技术制备了SiC/BN复相陶瓷。研究发现:该混合前驱体进行共热解时,二者的相互交联作用有利于提高前驱体的陶瓷产率。同时发现,BN前驱体可以抑制PCS热解后SiC晶粒的生长。随着BN前驱体含量的增加,对SiC晶粒的抑制作用越明显,在适当的比例下,于1100 °C热解可以得到非晶态SiC/BN陶瓷。但是,当BN含量过高时,反而促进SiC晶粒的析出。分析认为,一定含量的B、N异质元素的引入可以阻碍陶瓷材料中Si、C等原子的扩散与迁移,从而抑制了SiC晶粒的析出和长大。而BN含量过高时,易形成非晶SiNC单元,该组元在较低温度下容易解离促使SiC析晶。 (2) 研究了非晶SiC/BN陶瓷的微观结构、热稳定性、析晶行为及其在高温热处理过程中的分解机理。研究发现:非晶SiC/BN陶瓷具有优良的热稳定性,在Ar气氛下其非晶态结构可以保持到1800 oC,失重仅为2.08%。随着热处理温度进一步提高,非晶陶瓷样品出现SiC、Si3N4的析晶和乱层结构炭的有序石墨化。其析晶机理主要是聚碳硅烷的基本结构单元(BSU)成核和长大。SiC/BN陶瓷经2000 oC、2200 oC热处理后出现明显的失重,这是由于非晶陶瓷网络中的Si–N键断裂和碳热还原反应共同作用,导致陶瓷材料发生分解所引起。 (3) 以CVI技术制备的低密度C/C复合材料为预制体,混合前驱体为浸渍剂,采用PIP技术制备较致密的Cf/C–SiC–BN复合材料。研究发现:在复合材料致密化初始阶段采用混合前驱体/二乙烯基苯(DVB)作浸渍剂,浸渍后期采用混合前驱体/二甲苯溶液体系作浸渍剂可以显著提高复合材料的致密化速率。所得Cf/C–SiC–BN复合材料基体均匀致密,无明显气孔,基体和纤维之间均匀分布,浸渍热解过程未对纤维造成明显的损伤。 (4) 考察了Cf/C–SiC–BN复合材料的力学性能。研究发现:前驱体热解升温速率和材料的组成对复合材料的力学性能均有影响。过低或过高的热解升温速率都会导致复合材料的力学性能下降,随着BN含量的增加,复合材料的弯曲强度缓慢下降,而断裂韧性有所提高。复合材料的弯曲强度和断裂韧性最高可达到218 MPa和8.64 MPa?m1/2,经1800 oC高温热处理后,其弯曲强度保留率达到92.8%,表现出良好的高温力学性能。复合材料失效形式为假塑性断裂,热解过程中SiC晶粒生长被抑制,减小了对碳纤维的损伤,纤维与基体的弱界面结合,使材料在承载过程中表现出裂纹偏转、纤维的脱粘、拔出等能量耗散形式,提高了材料的力学性能。 (5) 考察了Cf/C–SiC–BN复合材料的氧化行为。研究发现:BN的引入显著提高了复合材料的抗氧化性能,适宜的BN含量可以使Cf/C–SiC–BN复合材料在较宽的温度范围具有良好的抗氧化能力。在低温阶段,复合材料随BN含量的升高,弯曲强度保留率逐渐增加;在高温阶段,复合材料的氧化性能具有选择性。Cf/C–SiC–BN复合材料的抗氧化机理为:在较低温度阶段,BN氧化生成的B2O3填充了氧化层表面的孔隙,而阻止了氧气的进入;在中温阶段,SiC氧化氧化生成的SiO2与B2O3反应形成硼硅酸玻璃态固溶体,因其挥发性小,氧在固溶体中的扩散系数比在B2O3中低,从而有效地阻止了氧气的进入;在更高的温度阶段,尽管在富B区域难以形成硼硅酸玻璃,因B2O3大量挥发使得复合材料的抗氧化性能有所下降,而具有较高稳定性的SiO2依然可以作为保护层阻止氧向材料内部扩散。 (6) 采用PIP工艺制备了单向SiCf/C–SiC–BN复合材料并研究其力学性能和抗氧化性能。研究发现:在1300–1500 °C范围,该复合材料几乎没有质量损失,其弯曲强度达到128 MPa,说明该材料是一种极具应用潜力的优异陶瓷基复合材料。 (7) 分别采用固相烧结和沉淀–喷雾造粒法制备以铬酸钴(CoCr2O4, CCR)为主相的热辐射防护粉体材料。研究发现,传统固相烧结法所得粉体存在成分偏析,其热辐射性能不及沉淀–喷雾造粒法所得的样品。以喷雾造粒所得材料制备的涂层,其全波段法向发射率在800 °C时达到0.92,具有良好的热辐射性能。 (8) 采用等离子喷涂的方法在Cf/C–SiC–BN复合材料上制备CCR热辐射涂层。研究发现:新型CCR涂层–Cf/C–SiC–BN整体复合材料对比Cf/C–SiC–BN复合材料,其抗氧化性能有了进一步的提高,并且整体复合材料在1300 °C和空冷的条件下,热震循环实验7次之后涂层保持完好,表现出良好的抗热震性能。
Other AbstractWith the development of advanced aero-engine, high-temperature ceramic composites with excellent oxidation resistance, mechanical properties and long life, find more and more important applications in the hot-section components such as turbine blade, combustion chamber and adjustment sheets. Carbon fiber reinforced carbon (C/C) matrix composites have been used as high-temperature structural materials for several decades and become the promising candidate materials for these high temperature applications due to their excellent properties of low density, high strength, high modulus, high thermal conductivity, low thermal expansion and so on. However, C/C ceramic composites are easily oxidized at elevated temperature in oxidation atmosphere. In addition, the high temperature anti-oxidation coatings of C/C composites exists many problems in technology and reliability such as the mismatch about the coefficient of thermal expansion between coatings and C/C composites, which have discounted their capacity as the protective coatings. These shortcomings limit the application of C/C composites as high temperature component materials. Therefore, it is necessary to modify the matrix materials by adding dispersed phase ceramics with excellent oxidation resistance combining anti-oxidation protective coatings to effectively obtain C/C ceramic matrix composites with long time anti-oxidation property and enough mechanical properties. In this study SiC and BN were employed to improve the oxidation resistance of C/C ceramic composites because of their outstanding properties. Thus SiC/BN ceramics were firstly fabricated by polymer-derived ceramic method. The pyrolysis process of polymers, the microstructures and properties of obtained ceramics and the crystallization and decomposition mechanism of the ceramics were investigated. Base on the previous results, the Cf/C–SiC–BN ceramic composites were fabricated. The influences of preparation techniques and composition on the microstructures, mechanical properties and oxidation resistance of the ceramic composites were investigated. The anti-oxidation mechanism of the ceramic composites was also discussed. Meanwhile, the thermal protective coatings of cobalt chromate (CCR) were prepared on the surface of Cf/C–SiC–BN ceramic composites. The mechanical and anti-oxidation properties of Cf/C–SiC–BN ceramic composites with thermal emissivity coatings were also investigated. The main results are as follows: (1) SiC/BN ceramics were fabricated by co-pyrolysis of the polymeric precursors of polycarbosilane and BN precursors synthesized in our group due to their mutual solubility. During co-pyrolysis process, it was found that the ceramic yield of the hybrid precursors was higher than those of single precursors due to the cross-linking effect between the two precursors. Addition of BN could obviously restrain the crystallization of SiC phase from PCS, and the formed grain size of SiC was related to the content of BN precursor added. Appropriate amount of BN precursors was favorable for the formation of amorphous SiC. However, it was not advantageous with uninterrupted increase that excess BN precursors were harmful to the formation of amorphous product, which could facilitate the crystallization of SiC.
Pages125
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/8298
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
骆丽杰. 高温抗氧化复合材料及其热防护涂层的制备与性能研究[D]. 中国科学院研究生院,2013.
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