连续碳化硅纤维增强碳化硅陶瓷基复合材料研究进展

碳化硅纤维增强碳化硅陶瓷基(SiC/SiC)复合材料具有轻质、耐高温、抗氧化的优异特性,在航空领域,如航空发动机的热端构件、高温结构功能一体化构件,航天及空天飞行器热防护结构部件、动力系统热端部件等领域具有广泛的应用前景,受到美国、欧洲、日本等国研究人员的广泛关注。本文从组成、制备工艺、加工工艺和考核应用等方面,综述了SiC/SiC复合材料的国内外研究进展,并指出了目前面临的问题和机遇。     

SiC短纤维增强SiC-BN复合陶瓷

采用原位合成的方法设计并制备了SiC短纤维增强的SiC—BN复合陶瓷。经理论计算及实验证明，在相对较低的温度(1700℃)下即可成功实现预期的原位反应，生成了细小均匀的微米级SiC和BN颗粒，并研究了纤维和BN含量对复合陶瓷组织结构和力学性能的影响。     

连续纤维增强陶瓷基复合材料界面研究进展

在陶瓷基复合材料中引入高强陶瓷纤维的目的是为了增强陶瓷的断裂韧性,纤维与基体的界面是决定CMC韧性的关键因素。国内外许多专家和机构研究重点主要集中于连续纤维增强陶瓷基复合材料的界面,包括纤维与基体的化学相容性和热物理相容性,以及用TEM、HRTEM、SADP、AEM、声学显微法、EDX等微观测试手段研究不同体系的界面形成机理。本文对上述界面研究概况进行了综述,并简述了界面设计原则和近年来计算机技术在界面研究中的应用情况。指出,连续纤维增强陶瓷基复合材料界面研究将一直是复合陶瓷基复合材料界研究的重点和难点。     

Oxidation Kinetics and Stress Effects for the Oxidation of Continuous Carbon Fibers within a Microcracked C/SiC Ceramic Matrix Composite

Carbon fiber-reinforced silicon carbide (C/SiC) composites have the potential to be utilized in many high-temperature structural applications, particularly in aerospace. However, the susceptibility of the carbon fibers to oxidation has hindered the composite's use in long-term reusable applications. In order to identify the composites limitations, fundamental oxidation studies were conducted to determine the effects of such variables as temperature, environment, and stress. The systematic studies first looked at the oxidation of the plain, uncoated carbon fiber, then when fiber was utilized within a C/SiC composite, and finally when a stress was applied to the C/SiC composite (stressed oxidation). The first study, oxidation of just the carbon fibers, showed that the fiber oxidation kinetics occurs in two primary regimes: chemical reaction control and diffusion control. The second study, oxidation of the C/SiC composite, showed the self-protecting effects from the SiC matrix at elevated temperatures when the composite was not stressed. The final study, stressed oxidation of the C/SiC composite, more closely simulated application conditions in which the material is expected to encounter thermal and mechanical stresses. The applied load and temperature will affect the openings of the as-fabricated cracks, which are an unavoidable characteristic of C/SiC composites. The main objective of the paper was to determine the oxidation kinetic regimes for the oxidation of carbon fibers in a cracked silicon carbide matrix under stressed and unstressed conditions. The studies help to provide insights in to the protective approaches, that could be used to prevent oxidation of the fibers within the composite.     

裂解碳包覆对SiC纳米纤维增强SiC陶瓷基复合材料性能的影响

以SiC纳米纤维(SiC_nf)为增强体,通过化学气相沉积在SiC纳米纤维表面沉积裂解碳(PyC)包覆层,并与SiC粉体、Al₂O₃-Y₂O₃烧结助剂共混制备陶瓷素坯,采用热压烧结工艺制备质量分数为10%的SiC纳米纤维增强SiC陶瓷基(SiC_nf/SiC)复合材料。研究了PyC包覆层沉积时间对SiC_nf/SiC陶瓷基复合材料的致密度、断裂面微观形貌和力学性能的影响。结果表明:在1 100 ℃下沉积60 min制备的PyC包覆层厚度为10 nm,且为结晶度较好的层状石墨结构;相比于纤维表面无包覆层的复合材料,复合材料的断裂韧性提高了35%,达到最大值(19.35±1.17) MPa·m^1/2,抗弯强度为(375.5±8.5) MPa,致密度为96.68%。复合材料的断裂截面可见部分纳米纤维拔出现象,但SiC_nf/SiC陶瓷基复合材料界面结合仍较强,纳米纤维拔出短,表现为脆性断裂。     

2D-SiC/SiC陶瓷基复合材料的拉伸本构模型研究

通过单向拉伸试验,研究了2D-SiC/SiC复合材料的应力-应变行为.结果表明,材料单向拉伸应力-应变曲线表现出明显的双线性特征,且线弹性段较长.通过试件断口照片,分析了2D-SiC/SiC复合材料单向拉伸破坏机理和损伤模式.基于对损伤过程的假设,建立了二维连续纤维增强陶瓷基复合材料的双线性本构模型,并将其应用于2D-SiC/SiC复合材料的应力-应变曲线模拟,模拟结果与试验值吻合很好.同时,分析计算表明,2D-SiC/SiC复合材料的单轴拉伸行为主要由纵向纤维柬决定,横向纤维对材料的整体模量和强度贡献很小.     

Low-Temperature Oxidation Embrittlement of SiC (Nicalon™)/CAS Ceramic Matrix Composites

The influence of extended duration (up to 1000 h), low temperature oxidation heat-treatments (375°–600°C) has been assessed using a model ceramic matrix composite system with a graphitic fiber/matrix interphase. For this study a Nicalon^™ fiber reinforced CaO–Al₂O₃–SiO₂ matrix composite was selected (Nicalon^™/CAS), which possesses a thin (∼20–40 nm) carbon-based interphase. Oxidation exposure has been conducted under both unloaded and static fatigue-loaded conditions. For unstressed oxidation exposure, degradation of the carbon-based interphase is apparent at temperatures as low as 375°C, after 1000 h exposure, resulting in a transition to a nominally brittle failure mode (i.e., negligible fiber pull-out). The degree of mechanical property degradation increases with increasing temperature, such that strength degradation, and a transition to nominally brittle failure, is apparent after just 10 h at 600°C. Static fatigue loading between 450° and 600°C demonstrated generally similar trends, with reduced lifetimes being observed with increasing temperature. Based upon the unloaded oxidation experiments, combined with previously obtained intermediate and high-temperature oxidation stability studies, a simple environmental embrittlement failure mechanism map is presented for Nicalon^™/CAS. The implications of this study for advanced composite designs with multiple thin carbon-based interphase layers are also discussed.     

碳纤维增强碳化硅陶瓷基复合材料的研究进展及应用

碳纤维增强碳化硅陶瓷基复合材料具有密度低、高强度、高韧性和耐高温等综合性能,已得到世界各国高度重视.本文综述了碳纤维的研究进展,C_f/SiC复合材料的制备方法,并分析了各种制备方法的优缺点.概述了C_f/SiC复合材料作为高温热结构材料和制动材料的应用状况.最后,指出了有待解决的问题和今后的主要研究方向.     

助熔剂对原位转化碳纤维增韧陶瓷基复合材料性能的影响

本文以聚丙烯腈(PAN)预氧化纤维为先驱体,以氧化铝为主要原料,添加SiO2-MgO-CaO三系助熔剂,采用真空热压烧结法制备了原位转化碳纤维增韧氧化铝复合材料.主要探讨不同助熔剂添加量对复合材料微观结构和各项性能指标的影响.以体积密度、显微硬度和断裂韧性等性能指标为主要评价标准选择最佳的助熔剂添加量.并研究了原位转化碳纤维增韧氧化铝陶瓷的摩擦磨损行为与机制以及力学性能和微观结构对摩擦磨损特性的影响.结果表明:当助熔剂含量为3vol％时,复合材料的综合性能最优,此时体积密度为3.72 g·cm-3,显微硬度为1624 HV,断裂韧性为10.6 MPa·m1/2.在室温干摩擦条件下,复合材料的磨损率随着助熔剂含量的增加呈先升高后降低趋势.室温下原位转化碳纤维增韧氧化铝基复合材料的磨损机制以脆性剥落为主,并伴有疲劳磨损.     

Lanxide陶瓷基复合材料的研究进展

Lanxide熔融金属直接氧化技术是一种新型的复合材料制备技术,通过用预制体(颗粒、晶须、纤维等)增强所制备的复合材料具有高的体积稳定性、断裂韧性和强度,是目前材料科学领域的热点之一.本文就Lanxide技术及陶瓷基复合材料近年来的最新发展进行了概述.     

Mechanical Properties of Thin Pyrolitic Carbon Interphase SiC–Matrix Composites Reinforced with Near-Stoichiometric SiC Fibers

Tensile properties of Tyranno™-SA near-stoichiometric silicon carbide (SiC)-fiber–reinforced chemically vapor-infiltrated SiC-matrix composites with pyrolytic carbon interphases were experimentally studied. The influence of interphase thickness in a range of 60–300 nm on the tensile properties of the materials appeared to be generally minor. Thin interphase (<100 nm) did not have a significant deteriorating effect on composite properties, which has commonly been reported for conventional SiC-fiber composites. For very thin interphase (<60 nm) composites, a slight decrease in fracture strain and a substantial increase in interfacial sliding stress were noted. Increases in ultimate tensile strength and fracture strain were observed at a much thicker interphase (>600 nm) at the expense of composite stiffness.     

无压烧结硼化锆基ZrB2-SiC复相陶瓷的结构与性能

以钇铝石榴石-YAG为烧结助剂,通过无压烧结制备了ZrB2-SiC复相陶瓷。研究了烧结助剂含量对烧结材料力学性能和显微结构的影响,材料的显微结构由扫描电镜SEM及其能谱分析EDS测定。研究结果表明,烧结助剂(YAG)和原料中的杂质形成玻璃相填充在晶界上,显著促进了硼化锆基ZrB2-SiC复相陶瓷的致密化。     

Tensile Properties of Ceramic Matrix Fiber Composites

The mechanical properties of various 2D ceramic matrix fiber composites were characterized by tension testing, using the gripping and alignment techniques development in this work. The woven fabric composites used for the test had the basic combinations of Al₂O₃ Fabric/Al₂O₃, SiC fabric/SiC, and SiC minofilament uniweave fabric/SiC. Tension testing was performed with strain gauge and acoustic emission instrumentation to identify the first-matrix cracking stress and assure a valid alignment. The peak tensile stresses of these laminate composites were about one-third of the flexural strengts. The SiC monofilament uniweave fabric (14 vol%)/SiC composites showed a relatively high peak stress of 370 MPa in tension testing.     

Oxidation Behavior of Hot Pressed ZrB2‐ZrC‐SiC Ceramic Composites

Dense ZrB₂‐SiC ceramics containing 40 vol% ZrC particles are fabricated via hot pressing method. Then the sintered ceramics are oxidized in air up to 1500°C, and the oxidation kinetics of the ceramic composites is deduced in combination with the reacted fraction curves. As indicated by the experimental results, the oxidation kinetics changes from reaction‐controlled process to diffusion‐controlled one with increasing of oxidation temperature. In addition, the oxidation kinetics parameters are obtained, which indicates that the oxidation resistance decays at elevated temperatures. Furthermore, the evolution of surface morphology and oxide scale during oxidation process is clarified.     

Low-Temperature Processing of Ceramic Woven Fabric/Ceramic Matrix Composites

Two-dimensional Al₂O₃ and SiC woven laminate composites, and oxide and nonoxide monolithic ceramics with 5 to 10 wt% of polycarbosilane binder, were consolidated up to 75% of TD (theoretical density) at 1150°C by the multiple impregnations of a polycarbosilane solution. The processing conditions were optimized without causing fiber damage. The near-net-shape composite fabricated by this process showed high reproducibility in terms of relative density and flexural strength. The mechanical properties were characterized by flexural testing with strain gauges. All of the woven laminate composites exhibited good composite-type fracture behavior, e.g., load-carrying capacity following maximum load. The room-temperature flexural strength and first-matrix cracking stress of SiC fabric/SiC composite with 73% TD were about 300 and 77 MPa, respectively.     

钛酸铝基复合陶瓷的研究

提出了钛酸铝陶瓷研究中存在的问题．论述了颗粒弥散强化陶瓷基复合陶瓷的机理，叙述了第二相颗粒补强钛酸铝基复合陶瓷的国内外研究状况．认为钛酸铝基复合陶瓷是一种很有前途的抗热震冲击且耐高温的材料，并指出了今后的研究方向。     

Melt Infiltration Approach to Ceramic Matrix Composites

Melt infiltration offers an alternative route to the synthesis of fully dense ceramic matrix composites. Necessary conditions with respect to chemical reactivity, melt viscosity, and wetting must be satisfied. Other properties of the reinforcement and matrix constituents must also be considered. With these restrictions this generic approach is applicable to a wide range of composite systems. Preliminary structure and property results are presented for the representative systems based on particulate and whisker SiC reinforcement in combination with CaSiO₃, SrSiO₃, and strontium feldspar matrices.     

Additive Manufacturing of SiCN Ceramic Matrix for SiC Fiber Composites by Flash Pyrolysis of Nanoscale Polymer Films

The potential of polymer‐derived ceramic matrices for silicon‐carbide fiber composites is demonstrated by additive layering of thin films on SiC fiber bundles. The thin liquid films, which naturally wet the fiber surfaces, are cross‐linked and pyrolyzed in‐situ into the silicon carbonitride ceramic in just a few seconds to yield defect‐free layers that are 10 to 100 nm thick. The infiltration is completed by repeating the cycles. A nearly fully dense and defect free SiCN matrix could be obtained. Room‐temperature tensile tests show a tensile strength of ~1200 MPa. Good matrix‐fiber interface behavior is seen with pull‐out character which is most likely responsible for the apparent ductility. The SiC fibers were uncoated.