SiC纤维及其增强SiCf/SiC复合材料的研究进展

SiC_f/SiC复合材料的低密度、耐高温、抗环境腐蚀及抗氧化等突出性能,使其在航天及空天飞行器的热端部件、热防护结构、发动机热端部件及核工业等领域取得了重大应用,是新一代最佳的高温结构材料。SiC纤维作为增强相,自身抗拉强度高、抗蠕变性能好、兼具耐高温、抗氧化等优点,且与陶瓷基体有着优异的相容性,可使陶瓷复合材料克服脆性,具有韧性,极大地推动了陶瓷复合材料的应用。文章以碳化硅纤维研发技术的三个重要发展阶段为例,详细阐述了碳化硅纤维的制备方法及性能特点,同时对碳化硅纤维增强陶瓷基复合材料的不同制备工艺进行了介绍,并分析了该复合材料当前国内外的应用现状,文章简述了SiC_f/SiC复合材料的发展及推广前景。     

连续SiC纤维增韧SiC基体复合材料研究进展

近年来,SiC纤维增韧SiC基体复合材料(SiC<,f>/SiC)由于具有良好的高温力学、抗化学腐蚀、高的韧性与抗中子辐照等优异性能而受到广泛关注.本文主要从纤维、界面层、基体与应用四方面评述了近年来国内外的研究进展.SiC纤维的性能直接影响了界面层材料与基体制备技术的选择.电泳沉积有望成为一种低成本、节能及对环境无污染的界向层及基体制备技术.在应用方面,作为热结构材料,SiC<,f>/SiC复合材料已经得到了实际应用.核反应堆用SiC<,f>/SiC结构材料的研究到了实际考核验证阶段.高性能SiC纤维的大规模生产是SiC<,f>/SiC广泛应用的前提条件.     

C/C复合材料抗氧化耐高温SiC陶瓷涂层的研究

采用高温反应法和PVD法在SiC工业合成炉内制备了C/C复合材料耐高温抗氧化SiC陶瓷涂层.用XRD、SEM对其物相组成和显微结构进行了表征与分析,讨论了涂层的形成机理,并研究了其高温氧化性能.研究结果表明,所制备的陶瓷涂层主要由α-SiCβ-SiC组成,晶粒发育完整,涂层表面致密、无裂纹,且与碳基体结合紧密,涂层厚度约600μm,涂层抗氧化性良好,在1500℃空气中氧化10h失重约为0.3%.     

陶瓷基复合材料的界面相容性研究

有关陶瓷基复合材料（CMC）的界面问题已经得到广泛的重视。为了使材料达到一个很好的刚性，在纤维与基体之间保持尽量小的界面作用力对于陶瓷纤维增强Si-C-O复合材料是非常重要的。在纤维界面上涂层有利于减小它们之间相互作用，涂层处理后的Si-C-O复合材料的弯曲强度比一般无涂层的复合材料高5倍。在介质涂层、基体、以及涂层与纤维间的三相物质中避免化学反应的发生。目前，可利用化学相容性的原理对涂层纤维进行选择。     

热解碳界面层对碳＼碳化硅复合材料拉伸性能的影响

本文研究了用化学气相渗工艺的均热法制备炭纤维增强碳化硅（Ｃ／ＳｉＣ）复合材料，其中有部分材料在沉积碳化硅之前先沉积少量热解碳，以作为界面层。对有界面层和无界面层的材料进行了拉伸试验。用金相显微镜和扫描电镜观察了材料微观结构及继口形貌。结果表明，Ｃ／ＳｉＣ材料力学性能主要取决于纤维与基体的界面。有热解碳界面层的Ｃ／ＳｉＣ材料，在拉伸断裂时出现大范围脱粘，断口类似毛刷，材料强度大，断裂功也大，有很大的     

SiC基层状复合材料界面层的选择

利用凝胶注模成型SiC基体层 ,以喷涂法、流延法、金属箔法、浸涂法分别加涂W ,W -2 % (质量分数 ,下同 )Co ,Ta,BN界面层 ,通过热压烧结制备了SiC/W ,SiC/W -2 %Co ,SiC/Ta ,SiC/BN层状复合材料 .在复合材料高温制备过程中 ,金属W ,W -2 %Co ,Ta与SiC反应生成了碳化物和硅化物 ,失去了金属塑性 ,未能实现裂纹尾流区桥接、残余应力增韧等金属界面层层状复合材料赖以大幅度提高其强韧性的增韧机制 ,其增韧效果仅与BN陶瓷界面层的增韧效果相当 .此外 ,研究表明 ,提高基体层力学性能可以显著提高层状复合材料的强韧性 .制备的SiC/BN层状复合材料的室温三点弯曲强度为 72 9.86± 114 .0 2MPa、室温断裂韧性为 2 0 .5 8± 2 .77MPa·m1 /2 ,其主要增韧机制包括裂纹分叉钝化、裂纹偏转、裂纹并行扩展以及裂纹尾流区片层拔出等     

单向复合材料C/SiC平面磨削力实验研究

纤维增韧陶瓷基复合材料由于优越的力学性能被广泛应用于航空航天等重大国防领域.为探究复合材料平面磨削的磨削力影响因素,设计制备了一种单向C/SiC复合材料,采用平面磨床对其典型方向进行磨削,结合磨削力物理模型对磨削力影响因素进行分析.此外,分析了材料的表面形貌和磨削机理.结果表明:磨削力与进给速度和磨削深度成正比,与砂轮转速成反比;磨削力遵循规律:法向>纵向>横向.纤维的各向异性是是造成磨削力各向差异的主要原因,此外加工过程中材料破坏以脆性断裂为主.研究结果可为提高复合材料磨削效率提供理论基础,同时可为多相复合材料研究提供一定借鉴作用.     

SiC陶瓷基体及抗氧化涂层

介绍了5种主要SiC基体的成型方法,分别是化学气相渗透(CVI)、聚合物先驱体浸渍-裂解法(PIP)、液相硅渗透法(LSI)、反应烧结法、化学气相反应法(CVR)。阐述了各种基体的组织结构、致密效率及陶瓷基复合材料的性能,其中CVI+PIP/LSI的复合成型技术可达到优化的制备过程,提高基体的组织结构和致密化效率;C/C及C/SiC复合材料表面化学气相转换法SiC涂层及多层涂层技术是提高CMC抗氧化性能的有效途径,并已得到工程实际验证。     

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。     

采用在SiC毡上CVD—SiC涂层提高C／C复合材料抗氧化性能

最近发展起来的SiC纤维复合涂层，也就是SiC/SiC层与化学气相沉积（CVD）SiC结合形成复合涂层，已能够在高温下提高C／C复合材料的抗氧化性。形成的SiC纤维复合涂层约300μm厚，生产时先将SiC毡覆盖在3D－C／C基体材料上，然后浸渍一种碳粉与硅粉均匀分散的料浆进行化学气要沉积。通过化学气相沉积（CVD）过程，在复合材料上形成致密的涂层。在CO2－H2O－N2组成的混合气体（CO2 9％、N273％、H2O18％），1700℃下进行5h氧化实验，结果发现有SiC毡增强复合涂层比没有SiC毡增强复合材料失重率低。SiC纤维毡复合涂层由双层结构组成，里层是多气孔的SiC/SiC纤维层，外层为致密的SiC涂层。由于SiC/SiC纤维层热膨胀系数介于C／C复合基体材料与CVD－SiC涂层之间，因此，SiC/SiC中间层在复合材料中起了重要作用，从而由于热膨胀系数不同产生的热应力致使涂层开裂降低到最低程度。涂层试样氧化后，采用缓冲冲床（MSP）测试其残余强度。MSP测试结果表明氧化后C／C复合材料强度值呈发散性，从纤维折断面看有z轴方向分布纤维存在。然而，这种方法仅适用于测试小尺寸试样。从这篇论文中，可看出涂层后的C／C复合材料有高的抗氧化性，其氧化后仍能保持高的残余强度。     

Enhancement of the microwave absorption properties of PyC-SiCf/SiC composites by electrophoretic deposition of SiC nanowires on SiC fibers

The employment of coating technique on the silicon carbide fibers plays a pivotal role in preparing SiC fiber-reinforced SiC composites (SiC_f/SiC) toward electromagnetic wave absorption applications. In this work, SiC nanowires (SiCNWs) are successfully deposited onto the pyrolytic carbon (PyC) coated SiC fibers by an electrophoretic deposition method, and subsequently densified by chemical vapor infiltration to obtain SiCNWs/PyC-SiC_f/SiC composites. The results reveal that the introduction of SiCNWs could markedly enhance the microwave absorption properties of PyC-SiC_f/SiC composites. Owing to the increasing of SiCNWs loading, the minimum reflection loss of composites raises up to −58.5 dB in the SiCNWs/PyC-SiC_f/SiC composites with an effective absorption bandwidth (reflection loss ≤ −10 dB) of 6.13 GHz. The remarkable enhancement of electromagnetic wave absorption performances is mainly attributed to the improved dielectric loss ability, impedance matching and multiple reflections. This work provides a novel strategy in preparing SiC_f/SiC composites with excellent electromagnetic wave absorption properties.     

Wear behavior of SiC nanowire-reinforced SiC coating for C/C composites at elevated temperatures

To improve the wear resistance of SiC coating on carbon/carbon (C/C) composites, SiC nanowires (SiCNWs) were introduced into the SiC wear resistant coating. The dense SiC nanowire-reinforced SiC coating (SiCNW-SiC coating) was prepared on C/C composites using a two-step method consisting of chemical vapor deposition and pack cementation. The incorporation of SiCNWs improved the fracture toughness of SiC coating, which is an advantage in wear resistance. Wear behavior of the as-prepared coatings was investigated at elevated temperatures. The results show that the wear resistance of SiCNW-SiC coating was improved significantly by introducing SiC nanowires. It is worth noting that the wear rate of SiCNW-SiC coating was an order of magnitude lower than that of the SiC coating without SiCNWs at 800 °C. The wear mechanisms of SiCNW-SiC coating at 800 °C were abrasive wear and delamination. Pullout and breakage of SiC grains resulted in failure of SiC coating without SiCNWs at 800 °C.     

Microstructure and strengthening behavior in high content SiC nanowires reinforced SiC composites

In this study, the high-content SiC_nw reinforced SiC ceramic matrix composites (SiC_nw/SiC CMC) were successfully fabricated by hot pressing β-SiC and sintering additive (Al₂O₃-Y₂O₃) with boron nitride interphase modification SiC_nw. The effects of sintering additive content and mass fraction (5–25 wt%) of SiC_nw on the density, microstructure, and mechanical properties of the composites were investigated. The results showed that with the increase of sintering additives from 10 wt% to 12 wt%, the relative density of the SiC_nw/SiC CMC increased from 97.3% to 98.9%, attributed to the generated Y₃Al₅O₁₂ (YAG) liquid phase from the Al₂O₃-Y₂O₃ that promotes the rearrangement and migration of SiC grains. The comprehensive performance of the obtained composite with 15 wt% SiC_nw possessed the optimal flexural strength and fracture toughness of 524 ± 30.24 MPa and 12.39 ± 0.49 MPa·m^1/2, respectively. Besides, the fracture mode of the composites with 25 wt% SiC_nw content revealed a pseudo-plastic fracture behavior. It concludes that the 25 wt% SiC_nw/SiC CMC was toughened by the fiber pull-outs, debonding, bridging, and crack deflection that can consume plenty of fracture energy. The strategy of SiC nanowires worked as a main bearing phase for the fabrication of SiC/SiC CMC providing critical information for understanding the mechanical behavior of high toughness and high strength SiC nanoceramic matrix composites.     

Short SiC fiber/Ti3SiC2 MAX phase composites: Fabrication and creep evaluation

The compressive creep of silicon carbide fiber reinforced Ti₃SiC₂ MAX phase with both fine and coarse microstructure was investigated in the temperature range of 1000-1300°C. Comparison of only steady-state creep was done to understand the response of fabricated composite materials toward creep deformation. It was demonstrated that the fibers are more effective in reducing the creep rates for the coarse microstructure by an increase in activation energy compared to the variant with a finer microstructure, being partly a result of the enhanced creep rates for the microstructure with larger grain size. Grain boundary sliding along with fiber fracture appears to be the main creep mechanism for most of the tested temperature range. However, there are indications for a changed creep mechanism for the fine microstructure for the lowest testing temperature. Local pores are formed to accommodate differences in strain related to creeping matrix and predominantly elastically deformed fibers during creep. Microstructural analysis was done on the material before and after creep to understand the deformation mechanics.     

Evaluation of SiC/SiC minicomposites with yttrium disilicate fiber coating

Hi‐Nicalon‐S/α‐Y₂Si₂O₇/SiC minicomposites were formed by polymer infiltration pyrolysis (PIP) and characterized by TEM, SEM fractography, tensile testing, and fiber push‐in testing. All minicomposites with α‐Y₂Si₂O₇ fiber coatings had strengths significantly higher than the control samples without fiber coatings. Extensive fiber pullout with debonding at the coating‐fiber interface or within the coating itself was observed in minicomposites with Y₂Si₂O₇ fiber coatings, but no debonding was observed in minicomposites without fiber coatings. Debond energies of 4.5 ± 3, 4.6 ± 3 J/m² and average sliding stresses of 91 ± 40, 94 ± 40 MPa were measured by fiber push‐in tests.     

Tribological performance of SiC coating for carbon/carbon composites at elevated temperatures

SiC coating was deposited on carbon/carbon (C/C) composites by chemical vapor deposition (CVD). The effects of elevated temperatures on tribological performance of SiC coating were investigated. The related microstructure and wear mechanism were analyzed. The results show that the as-deposited SiC coating consists of uniformity of β-SiC phase. The mild abrasive and slight adhesive wear were the main wear mechanisms at room temperature, and the SiC coating presented the maximum friction coefficient and the minimum wear rate. Slight oxidation of debris was occurred when the temperature rose to 300?°C. As the temperature was above 600?°C, dense oxide film formed on the worn surface. The silica tribo-film replaced the mechanical fracture and dominated the frication process. However, the aggravation of oxidation at elevated temperatures was responsible for the decrease of friction coefficient and the deterioration of wear rate. The SiC coating presented the minimum friction coefficient and the maximum wear rate when the temperature was 800?°C.     

Cf/SiC复合材料的制备及性能的研究

采用料浆渗积-有机前躯体裂解工艺制备碳纤维增强碳化硅陶瓷基复合材料.制备材料的抗弯强度达283 MPa,断裂韧性达12.1 MPa·m1/2.     

Synthesis of coatings on SiC fibers and their effects on microstructure and mechanical properties of SiCf/SiBCN composites

In this study, the amorphous C, ZrB₂, and BN single-layer coatings as well as C/BN, C/ZrB₂, ZrB₂/BN, and C/ZrB₂/BN composite coatings were prepared on SiC fibers (SiC_f) by an in situ synthesis and solution impregnation–pyrolysis method. Subsequently, SiC_f/SiBCN composites were fabricated by hot-pressing sintering at 1900℃/60 MPa/30 min to explore the influence of different coatings on the microstructure and mechanical performance of resulting composites. After the preparation of single-layer-coated SiC_f, the SiC_f(BN) or SiC_f(ZrB₂) tended to be overlapped with each other, whereas the dispersion of amorphous C–coated SiC_f was satisfying. Besides, some uneven areas and attached particles have appeared on fiber surfaces of the SiC_f(BN) or SiC_f(ZrB₂), whereas smooth and dense surfaces of amorphous C–coated SiC_f were observed. Because the uniformity of ZrB₂ coatings can be partially damaged by the subsequent coating process of BN, the composite coatings of ZrB₂/BN and C/ZrB₂/BN were thereby not suitable for strengthening SiBCN matrix. The SiC_f/SiBCN composites with C/ZrB₂ coatings have desirable comprehensive mechanical properties. Nevertheless, the conventional toughening mechanisms such as fiber pull-out and bridging, and crack deflection are not available for these composites because the serious crystallization of SiC_f leading to great strength loss, resulting in catastrophic brittle fracture.     

Microstructures and oxidation behaviors of Al-modified and Al2O3-modified SiC coatings on carbon/carbon composites via pack cementation

Al₂O₃-modified SiC (AOSC) and Al-modified SiC (ASC) coatings were prepared on carbon/carbon (C/C) composites by one-time pack cementation (PC). Their microstructures and anti-oxidation performances were studied. Compared with ASC coating, AOSC coating shows more conspicuous defects (micro-cracks and holes) and lower densification. ASC coating can offer better oxidation resistance and thermal shock resistance to C/C composites than AOSC coating. Al additive can more efficiently improve the sinterability of SiC, which causes the above results. Besides, Al₂O₃ oxidation product is more stable than SiO₂ (l) of oxidized SiC at 1500 °C based on the thermodynamic analysis.     

Effect of SiC coating and heat treatment on the thermal radiation properties of C/SiC composites

The effects of SiC coating and heat treatment on the emissivity were investigated for 2D C/SiC composites prepared by CVI in the 6–16 μm range. SiC coating had an obvious effect on the spectral emissivity of the composites but caused just 5% difference in the total emissivity. A radiation transport model was applied to explain those changes caused by SiC coating. Heat treatment affected the thermal radiation properties of the composites through the microstructure evolution. Base on the complementary analytical techniques, the changes in the emissivity were attributed to a good graphitization degree of carbon phases, large β-SiC grain sizes and high α-SiC content resulting in high emissivity.