Preparation, Properties and Application of C/C-SiC Composites Fabricated by Warm Compacted-in situ Reaction

Carbon fibre reinforced carbon and SiC dual matrices composites (C/C-SiC) show superior tribological properties, high thermal shock resistance and good abrasive resistance, and they are promising candidates for advanced brake and clutch systems. The microstructure, mechanical properties, friction and wear properties, and application of the C/C-SiC composites fabricated by warm compacted-in situ reaction were introduced. The results indicated that the composites were composed of 50-60 wt pct carbon, 2-10 wt pct residual silicon and 30-40 wt pct silicon carbide. The C/C-SiC brake composites exhibited good mechanical properties. The value of flexural strength and compressive strength could reach 160 and 112 MPa, respectively. The impact strength was about 2.5 kJ·m^-2. The C/C-SiC brake composites showed excellent tribological performance, including high coefficient of friction (0.38), good abrasive resistance (1.10 μm/cycle) and brake steadily on dry condition. The tribological properties on wet condition could be mostly maintained. The silicon carbide matrix in C/C-SiC brake composites improved the wear resistance, and the graphite played the lubrication function, and right volume content of graphite was helpful to forming friction film to reduce the wear rate. These results showed that C/C-SiC composites fabricated by warm compacted-in situ reaction had excellent properties for use as brake materials.     

Investigation of the effect of surface modifications on the mechanical properties of basalt fibre reinforced polymer composites

Unsaturated polyester-based polymer composites were developed by reinforcing basalt fabric into an unsaturated polyester matrix using the hand layup technique at room temperature. This study describes basalt fibre reinforced unsaturated polyester composites both with and without acid and alkali treatments of the fabrics. The objective of this investigation was to study the effect of surface modifications (NaOH & H₂SO₄) on mechanical properties, including tensile, shear and impact strengths. Variations in mechanical properties such as the tensile strength, the inter-laminar shear strength and the impact strength of various specimens were calculated using a computer-assisted universal testing machine and an Izod Impact testing machine. Scanning Electron Microscope (SEM) observations of the fracture surface of the composites showed surface modifications to the fibre and improved fibre–matrix adhesion. The result of the investigation shows that the mechanical properties of basalt fibre reinforced composites are superior to glass fibre reinforced composites. This work confirms the applicability of basalt fibre as a reinforcing agent in polymer composites.     

炭纤维增强C/SiC双基体复合材料的制备及性能(英文)

以针刺炭纤维整体毡为预制体,联用化学气相沉积法与熔融渗硅法制得炭纤维增强C/SiC双基体(C/C-SiC)复合材料;研究了C/C-Si材料的显微结构、力学性能和不同制动速度下的摩擦磨损性能及机理。结果表明:C/C-SiC材料具有适中的纤维/基体界面结合强度,弯曲强度和压缩强度分别达240MPa和210MPa,具有摩擦系数高(0.41～0.54),磨损小(0.02cm3/MJ),摩擦性能稳定等特点.随着制动速度提高,C/C-Si材料的摩擦磨损机制也随之变化:在低速制动条件下主要表现为磨粒磨损;中速时以黏着磨损为主;高速时以疲劳磨损和氧化磨损为主。     

短纤维增强C/C-SiC复合材料的微观结构与力学性能EI北大核心CSCD

综合原料的热物理性能分析和配比设计,实现了C/C复合材料载体孔隙体积的精细控制,采用热压-熔渗两步法在低温条件下制备了具有高致密、低残余Si含量特征的短碳纤维增强C/C-SiC复合材料。系统解析了C/C-SiC复合材料成型过程中的结构演变行为,研究了短纤维增强C/C-SiC复合材料的力学性能和失效机制。结果表明:多孔C/C复合材料载体孔隙的孔径呈双极分布特征,添加芳纶纤维可提高网络孔隙结构的连通性,具有显著的孔隙结构调控作用。SiC基体以网络骨架形态分布于C/C-SiC复合材料内部,与纤维束形成了强界面结合钉扎结构,高含量纤维协同作用下使C/C-SiC复合材料具有优异的综合力学性能,添加芳纶纤维可明显增加复合材料内部裂纹扩展路径,提高C/C-SiC复合材料的断裂韧性。碳纤维的面内各向同性分布及陶瓷相层间均匀分布对C/C-SiC复合材料承载、摩擦稳定性提升均具有积极作用。     

浆料浸渍法制备C/C-SiC-ZrB2超高温复合材料及其烧蚀性能研究

采用浆料浸渍法引入ZrB₂微粉作为耐超高温相, 以炭纤维为增强体, 以热解炭和SiC为基体, 制备了ZrB₂含量不同的耐超高温C/C-SiC-ZrB₂复合材料; 通过电弧风洞考核材料的抗烧蚀性能, 通过XRD、SEM和EDS分析材料的烧蚀机理。结果表明: 在Ma 6电弧风洞条件下, C/C-SiC-ZrB₂复合材料的抗烧蚀性能优于C/C-SiC, 且随着ZrB₂含量的增加, 抗烧蚀性能随之提高; 在高温阶段形成的ZrO₂-SiO₂玻璃态熔融层起到了抗氧化烧蚀的作用。     

Mit TiN-Partikeln Lasermodifizierte Al2O3-Keramik im reversierenden Gleitkontakt unter Variation der Luftfeuchte und Temperatur

With TiN particles lasermodified Al₂O₃ ceramic under oscillating sliding contact at different humidities and temperatures A slightly porous, commercially available alumina ceramic was surface modified up to 170 μm thickness by adding TiN particles. The multiphase surface structure of this laser treated ceramic consisted of about 12 vol.% TiN, 16 vol.% grain boundary phase and 72 vol.% Al₂O₃. Tribological tests on the modified ceramic and for reference also on a highly dense alumina and titania were carried out in oscillating sliding contact against Al₂O₃ balls. In these tests, the temperature of the specimens was varied between 28°C and 500°C. At room temperature the relative humidity of the surrounding air was changed between 3% and 70% and additional tests were run by using distilled water as interfacial medium. The resulting multiphase microstructure showed substantially reduced friction and wear at different temperatures and also above relative humidities of about 35% at room temperature compared with the highly dense, commercially available alumina.     

Effect of Short Fibre Reinforcement on the Friction and Wear Behaviour of Nylon 66

Use of thermoplastic composite material for load bearing components is increasing due to economical processing of complicated shapes in large quantities. Addition of fibre improves the strength and modulus of composites. Although the tribo-behaviour of thermoplastic composites were investigated, the friction and wear mechanisms are not yet fully understood. Friction and wear behaviour of injection unfilled Nylon 66, glass fibre reinforced Nylon 66 and carbon fibre reinforced Nylon 66 is investigated under dry sliding conditions. Tests were conducted at different normal loads and sliding velocities at room temperature. Coefficient of friction, wear loss and heat generation during the wear tests were quantified. Presence of fibre affects coefficient of friction and wear resistance of Nylon 66 matrix composites. The formation and stability of the transfer films affects the wear resistance. The rise in temperature during sliding was also calculated and also measured. The contact temperature rise is influenced by the composition which in turn influences the fibre adhesion and thereby the wear resistance. Glass fibre reinforced Nylon exhibited the lowest wear rate among the materials investigated. Both adhesive and abrasive wear mechanisms were observed in polymer matrix composites.     

Influence of Fibre Orientation on Friction and Sliding Wear Behaviour of Jute Fibre Reinforced Polyester Composite

Jute fibre reinforced polyester composites were developed and characterized for friction and sliding wear properties. Effect of fibre orientation and applied load on tribological behaviour of jute fibre reinforced polyester composites were determined. It is found that wear resistance was maximum in TT sample, where fibres were normal to sliding direction. Wear rate under sliding mode follows this trend; W_TT < W_LT <W_LL LL sample showed higher capability to sustain the load whereas lowest wear resistance found in this case. The coefficient of friction found highest for TT sample and lowest for LT sample. The coefficient of friction decreased with increase of applied load. Worn surfaces were analysed and discussed with the help of SEM.     

Mechanical and tribological properties of zinc-aluminium metal-matrix composites

Recently, commercial Zn-Al foundry alloys such as ZA-27 have found increasing use for many applications and have competed effectively against copper, aluminium and iron-based foundry alloys. However, the elevated temperature (> 100°C) properties of zinc-aluminium alloys are unsatisfactory and restrict their use in some applications. One viable approach to improving the elevated temperature properties is to reinforce the zinc-aluminium alloys with alumina fibres. In this investigation, the mechanical properties of a Zn-Al alloy reinforced with alumina fibres were evaluated. Tensile, compression and impact properties were determined at 25, 100 and 150°C. Lubricated wear tests were also performed on the unreinforced alloy and composites. It was found that although fibre reinforcement did result in some improvement of tensile and compression properties at elevated temperatures, the composites had poor toughness and ductility. The presence of a brittle SiO₂ layer at the fibre/matrix interfaces resulted in fibre/matrix decohesion under tensile loading, impairing the performance of the reinforced materials. Some improvement in wear resistance was noted for the composite materials but fibre reinforcement did not yield significant improvement in fatigue resistance.     

Investigation of the mechanical behaviour of magnesium composites

Stress/strain and fracture toughness behaviour of a commercial heat-treatable magnesium alloy reinforced with up to 20 volume% short alumina fibres was studied at room and elevated temperatures. Microscopic examination of the composites, which were prepared by conventional squeeze casting, revealed damage of a small portion of the fibres during the infiltration process. Sufficient chemical reaction between the matrix alloy and alumina reinforcement tends to produce a good bond at the fibre/matrix interface. The tensile-related properties of the composites increased at room and elevated temperatures with increasing content of the reinforcement. The ductility and fracture toughness of the composites decreased at room temperature with increasing reinforcement content. While failure strains of the composites were slightly improved at higher testing temperatures, the fracture toughness decreased significantly as the testing temperature exceeded 100°C. Examination of the fracture surfaces of specimens tested at room temperature showed a mixed mode fracture appearance with predominantly brittle cleavage fracture. The fracture surfaces of specimens tested at temperatures above 100°C revealed increasing fibre/matrix interface debonding and fibre pull-out with increasing testing temperature. Micromechanism examinations of crack initiation and propagation indicated that the fracture process of the composites may be matrix controlled.     

C/C-SiC复合材料熔融渗硅制备工艺

C/C-SiC复合材料具有许多优异的性能,如高比强度、高比模量、优良的高温性能、高热导率以及低热膨胀系数等.与其它制备工艺相比,采用熔融渗硅法制备C/C-SiC复合材料的工艺具有操作简单、周期短、成本低等优点.综述了目前熔融渗硅法制备C/C-SiC复合材料的研究状况.     

Flax fibre and its composites – A review

In recent years, the use of flax fibres as reinforcement in composites has gained popularity due to an increasing requirement for developing sustainable materials. Flax fibres are cost-effective and offer specific mechanical properties comparable to those of glass fibres. Composites made of flax fibres with thermoplastic, thermoset, and biodegradable matrices have exhibited good mechanical properties. This review presents a summary of recent developments of flax fibre and its composites. Firstly, the fibre structure, mechanical properties, cost, the effect of various parameters (i.e. relative humidity, various physical/chemical treatments, gauge length, fibre diameter, fibre location in a stem, oleaginous, mechanical defects such as kink bands) on tensile properties of flax fibre have been reviewed. Secondly, the effect of fibre configuration (i.e. in forms of fabric, mat, yarn, roving and monofilament), manufacturing processes, fibre volume, and fibre/matrix interface parameters on the mechanical properties of flax fibre reinforced composites have been reviewed. Next, the studies of life cycle assessment and durability investigation of flax fibre reinforced composites have been reviewed.     

熔融渗硅法制备C/C-SiC复合材料的研究进展

综述了熔融渗硅法制备C/C-SiC复合材料的国内外研究和应用现状,重点分析了碳纤维预制体和C/C多孔体的制备,以及熔融渗硅过程对C/C-SiC复合材料性能和结构的影响,介绍了C/C-SiC复合材料作为热结构和摩擦材料在航空航天和先进摩擦制动系统中的应用,提出了C/C-SiC复合材料制备过程中存在的问题和今后研究的重点.     

CVI-GSI工艺制备C/C-SiC复合材料的组成结构与力学性能

采用密度为1.0g/cm~3的C/C素坯,联合化学气相渗透(CVI)和气相渗硅(GSI)2种工艺制备C/C-SiC复合材料,研究CVI C/C-SiC复合材料中间体的密度对CVI-GSI C/C-SiC复合材料物相组成、微观结构及力学性能的影响。结果表明:随着CVI C/C-SiC复合材料中间体密度的增大,CVI-GSI C/C-SiC复合材料C含量增多,残余Si含量减少,SiC含量先增多后减少,CVI-GSI C/C-SiC复合材料的密度先增大后减小;随着CVI C/C-SiC复合材料中间体的密度由1.27g/cm~3增加到1.63g/cm~3时,得到的CVI-GSI C/C-SiC复合材料的力学性能先升高后降低。当CVI C/C-SiC复合材料密度为1.42g/cm~3时,制得的CVI-GSI C/C-SiC复合材料力学性能最好,其弯曲强度为247.50MPa,弯曲模量为25.63GPa,断裂韧度为10.08MPa·m~(1/2)。     

Mechanical behaviour and microstructural characterization of 3D four‐directional braided SiO2f/SiO2 composites

In this paper, SiO_2f/SiO₂ composites reinforced by 3D four‐directional braided quartz preform were prepared by the silica sol‐infiltration‐sintering method in a relatively low sintering temperature (450 °C). To characterize the mechanical properties of the composites, mechanical testing was carried out under various loading conditions, including tensile, flexural and shear loading. The microstructure and the fracture behaviour of the 3D four‐directional braided SiO_2f/SiO₂ composites were studied. The tensile strength, flexural strength and the in‐plane shear strength were 30.8 MPa, 64.0 MPa and 22.0 MPa, respectively. The as‐fabricated composite exhibited highly nonlinear stress–strain behaviour under all the three types of loading. The tensile and flexural fracture mechanisms were fully discussed. The fracture mode of the 3D four‐directional braided SiO_2f/SiO₂ composite in the Iosipescu shear testing was based on a mixed mechanism because of the multi‐directivity of the composite. Owing to low sintered temperature, the fibre/matrix interfacial strength was weak. The SiO_2f/SiO₂ composites showed non‐catastrophic behaviour resulting from extensive fibre pull‐out during the failure process.     

Mechanical properties and microstructure of a P/M aluminium matrix composite with δ-alumina fibres and their relation to extrusion

Saffil short fibre-reinforced aluminium composites have been prepared via a powder metallurgy route. Three different reduction ratios of extrusion were investigated. The tensile mechanical properties at room and elevated temperature and the microstructure, with emphasis on fibre length, were evaluated. The reduction ratio did not influence mean fibre length, implying that during the extrusion the main fibre breakage occurred in the initial compaction stage. The relative strengthening of the unidirectionally reinforced composites at room temperature is low and depends on extrusion reduction ratio. At elevated temperature the strength of the composites in the longitudinal direction is significantly higher compared to that of the base alloy. At 250°C, improvements were obtained of 15%, 24% and 43% for V _f = 0.048, 0.100 and 0.200, respectively. It is suggested that strengthening is possible by the combined effect of a high ductility of the matrix and the resistance to plastic flow exerted by dislocations and stress fields around aligned fibres. All composites contain highly fibre-enriched layers, with bad internal cohesion. They originate from fibre clusters and form severe macroscopic defects during machining operations. Despite that, the tensile properties in the longitudinal direction are reasonably good.     

ZrB2-SiC复相陶瓷涂层制备及其保护C/C-SiC复合材料性能

为提高C/C-SiC复合材料的超高温抗烧蚀性能,通过浆料涂刷和高温烧结相结合的方法在C/C-SiC复合材料表面制备了ZrB₂-SiC复相陶瓷涂层,利用EDS、SEM对涂层的成分及微观形貌进行了分析。对涂层材料的力学性能和抗烧蚀性能进行了表征,结果表明：制备的ZrB₂-SiC复相陶瓷涂层保护C/C-SiC复合材料的拉伸强度、弯曲强度及剪切强度分别为147 MPa、355 MPa和21.9 MPa,与无涂层保护的针刺C/C-SiC复合材料的力学性能相比略有下降。涂层材料具有良好的抗氧化烧蚀性能,经过热流密度为3 200 kW/m²的氧乙炔火焰烧蚀600 s试验,其线烧蚀率和质量烧蚀率分别为0.001 mm/s和0.0006 g/s。     

Silicon carbide fibre reinforced glass-ceramic matrix composites exhibiting high strength and toughness

Silicon carbide fibre reinforced glass-ceramic matrix composites have been investigated as a structural material for use in oxidizing environments to temperatures of 1000° C or greater. In particular, the composite system consisting of SiC yarn reinforced lithium aluminosilicate (LAS) glass-ceramic, containing ZrO₂ as the nucleation catalyst, has been found to be reproducibly fabricated into composites that exhibit exceptional mechanical and thermal properties to temperatures of approximately 1000° C. Bend strengths of over 700 MPa and fracture toughness values of greater than 17 MN m^–3/2 from room temperature to 1000° C have been achieved for unidirectionally reinforced composites of 50 vol% SiC fibre loading. High temperature creep rates of 10^–5 h^–1 at a temperature of 1000° C and stress of 350 MPa have been measured. The exceptional toughness of this ceramic composite material is evident in its impact strength, which, as measured by the notched Charpy method, has been found to be over 50 times greater than hot-pressed Si₃N₄.     

Comparative analysis of wear behavior of garnet and fly ash reinforced Al7075 hybrid composite

Al7075 hybrid composites reinforced with varying weight percentage (0 wt.%, 5 wt.%, 10 wt.%, 15 wt.%) of each of garnet and fly ash were fabricated and characterized for their comparative wear assessment. The sliding wear test was conducted on a reciprocating tribometer in dry medium under the working conditions of applied normal load (2 N, 4 N, 6 N, 8 N), sliding velocities (0.04 m/s, 0.08 m/s, 0.12 m/s, 0.16 m/s), sliding distance (20 m, 40 m, 60 m, 80 m) and working temperature (25 °C, 50 °C, 75 °C, 100 °C). The experiments were performed as per steady‐state condition and Taguchi (L₂₅) orthogonal array design to evaluate specific wear rate of the Al7075 hybrid composites. The finding of results indicated that the wear rate was decreased with the increase in the filler content in both the case of garnet and fly ash reinforced Al7075 hybrid composites. The results from Taguchi experiments suggested that the filler content and load were the most significant factors affecting wear behavior of composites while temperature and sliding distance are the least significant factors. Also, the garnet reinforced Al7075 hybrid composite indicated less specific wear rate as compared to that of fly ash reinforced Al7075 hybrid composite.     

考虑孔隙和微裂纹缺陷的C/C-SiC编织复合材料等效模量计算

通过观察C/C-SiC复合材料组元分布的扫描电子显微镜(SEM)照片 , 获得了C/C-SiC复合材料化学气相渗透(CVI)制备过程中产生孔隙和微裂纹的几何信息。在此基础上 , 建立了包含孔隙和微裂纹的C/C-SiC微结构有限元模型 , 并利用均匀化等效计算方法预测了平纹编织C/C-SiC复合材料的模量。针对CVI沉积方式制备的2组不同的C/C-SiC复合材料 , 实验测试与等效计算结果表明 : 基于 SEM照片建立的C/C-SiC纤维束和复合材料微结构有限元模型 , 能够反映CVI工艺制备C/C-SiC中孔隙和微裂纹的分布状况; 计算结果与实验数据有良好的一致性 , 数值计算可有效预测C/C-SiC编织复合材料的模量。