Oxidation behaviour and protection of carbon/carbon composites

The oxidation behaviour of carbon/carbon composite materials and graphite (in cube form), in flowing air, has been studied in the temperature range 500 to 1100 °C. Gasification for unprotected samples occurred at temperatures around 500 °C. SiC coatings offered only limited protection below their intrinsic protection range due to the diffusion of oxygen along microcracks. Diffusional control was more significant for thicker coatings. However, the use of boron oxide applied on an underlayer of SiC, gave good protection for extended periods at temperatures up to 1000 °C, due to microcrack sealing. The use of borate coatings, both with and without an SiC underlayer, was limited by the volatility of the borate.     

Oxidation behaviour of three-dimensional woven C/SiC composites

Abstract

The oxidation behaviour of a three-dimensional woven C/SiC composite protected with an SiC seal coating and with an SiC coating combined with an SiO₂–B₂O₃ glassy coating have been respectively investigated through an experimental approach based on mass and flexural strength changes. Three main temperature domains exist for C/SiC composites protected with an SiC seal coating. At low temperatures (<700°C), the mechanisms of reaction between carbon and oxygen control the oxidation kinetics. At an intermediate temperatures (between 700 and 1100°C), the oxidation kinetics are controlled by gas phase diffusion through a network of microcracks in the SiC matrix and coating. At high temperatures (>1100°C), the oxidation kinetics are controlled by oxygen diffusion through the SiO₂ scale formed on the SiC coating. Composites of C/SiC with an SiC/(SiO₂–B₂O₃) coating exhibit better oxidation resistance. The filling of the pores and the microcracks and the flow of the glassy coating at higher temperatures result in a global decrease of mass loss in the composites. By researching the relationship between the residual flexural strength and the mass variation in different temperature ranges, it is shown that the change in the residual flexural strength is dominated by the degradation of carbon phase.     

Sliding wear behaviour of SiC particle reinforced 2024 aluminium alloy composites

Abstract

Sliding wear tests on SiC particle reinforced 2024 aluminium alloy composites fabricated by a powder metallurgy technique were carried out, and the effects of SiC particle content, size, and the wear load on the wear properties of the composites were systematically investigated. It was found that the wear resistance of the composites was about two orders of magnitude superior to that of the unreinforced matrix alloy, and increased with increasing SiC particle content and size. Under the conditions of sliding wear used, the effect of SiC particle size on the wear resistance was more significant than that of particle content.

MST/3161     

碳/碳复合材料SiC/MoSi_2/ZrO_2涂层体系氧化烧蚀性能

抗氧化涂层技术是解决碳/碳复合材料高温抗氧化性的最有效技术途径之一。为了提高材料在1 800℃以上的高温抗氧化性能,首次采用包埋法、涂刷法和等离子喷涂法在碳/碳复合材料表面制备出SiC/MoSi_2/ZrO_2梯度抗氧化涂层体系。采用SEM/EDS、结合力和粗糙度测试对涂层表面及断面形貌进行微观分析,利用等离子风洞对整个涂层体系进行氧化试验。结果表明:基体、过渡层和高温抗氧化层之间结合力良好,高温抗氧化层厚度均匀、结构致密。经等离子风洞氧化600s后,涂层表面温度达到1 850℃,氧化质量失重速率仅为3.15×10~(-6) g/(cm~2·s)。表明SiC/MOSi_2/ZrO_2梯度抗氧化涂层体系在1 800℃以上的高温环境下具有很好的抗氧化性能。     

Effect of particle size on fatigue behaviour in SiC particulate-reinforced aluminium alloy composites

The effect of particle size on rotary bending fatigue behaviour was studied for powder metallurgy 2024 aluminium alloy composites reinforced with 10 wt% silicon carbide particles (SiC_p ). Average particle sizes of 5, 20 and 60 μm were evaluated. Particle size had a significant influence on fatigue strength, indicating an increased fatigue strength with decreasing particle size. The composite with 5 μm SiC particles showed higher fatigue strength than the unreinforced alloy. The incorporation of 20 μm SiC particles led to an increase in fatigue strength at a high stress level, but the improvement diminished with decreasing stress level, and a slightly decreased fatigue strength was observed at low stress level, as compared with the unreinforced alloy. The composite with 60 μm SiC particles exhibited a considerable decrease in fatigue strength. Fatigue cracks initiated at several different microstructural features, e.g. surface defects, inclusions and particle–matrix interfaces, and crack initiation was considerably affected by particle size. Fatigue strength was found to depend strongly on the resistance to crack initiation, because there was no discernible difference in small crack growth between the unreinforced alloy and the composites, particularly at a low maximum stress intensity factor.     

SiC/SiC复合材料在高温空气中的氧化行为

连续碳化硅纤维增强碳化硅复合材料(SiC/SiC)是先进航空发动机热端部件的重要候选材料.在高温燃气环境中,SiC/SiC会发生氧化腐蚀,导致材料性能迅速恶化.为了揭示国产SiC/SiC复合材料在高温燃气环境中的氧化腐蚀行为,本工作测试了SiC/SiC复合材料的1100～1300℃空气氧化性能,获得了材料的氧化动力学曲线,利用SEM,XPS和XRD分析了材料的形貌、成分和物相演变规律,以阐明其氧化行为.结果表明:SiC/SiC复合材料在1100～1300℃的氧化动力学均遵循抛物线规律;其氧化物为SiO2.SiC/SiC在1100℃时仅发生轻微氧化,温度高于1200℃时复合材料的氧化程度随温度升高而加剧.在BN界面相和基体孔隙附近的氧化现象更为明显.SiC/SiC复合材料的弯曲强度随氧化程度增加而降低.     

Effect of SiC content and sliding speed on the wear behaviour of aluminium matrix composites

In the present study effect of SiC content and sliding speed on the wear behaviour of aluminium alloy and composite was studied using pin-on-disc apparatus against EN32 steel counterface. These tests were conducted at varying SiC particles in 10, 15 and 25 wt.% and sliding speeds of 0.52, 1.72, 3.35, 4.18 and 5.23 m/s for a constant sliding distance of 5000 m. The results revealed that as the SiC content increases the wear rate and temperature decreases, but reverse trend can be observed for coefficient of friction. All these facts can be discussed on the basis of prevailing wear mechanism.     

An approach to the mechanical behaviour of SiC/SiC and C/SiC ceramic matrix composites

The mechanical behaviour of two woven composites C/SiC and SiC/SiC was investigated at room temperature. The non-linear load-displacement curves and the damaging process were closely related to the specific structure of the composites, consisting of a network of impregnated bundles of fibres. The damage in the bundles proceeded by multiple cracking in the matrix before fibre failure, and dictated the response to the applied load. Other mechanisms, consisting mainly of distortions in bundles and their framework, induced a residual deformation and an energy dissipation. The behaviour was characterized according to the damaging process. Stress-electric strain curves revealed a mechanical response similar to those observed in unidirectional composites, although some effect of the specimen geometry on the curves was observed. Residual strains were similar in tensile and bending conditions. The work of fracture was consistently described by a volumetric rate of energy absorption, related to the applied strain, but the respective contributions of different damage mechanisms could not be determined.     

Investigation of impact behaviour of aluminium based SiC particle reinforced metal–matrix composites

In this paper, the impact behaviour of aluminium and silicon carbide (SiC) particle reinforced aluminium matrix composites under different temperature conditions was determined. Charpy impact tests were performed on as extruded and heat treated specimen at temperatures varying from −176 to 300 °C. Composite specimens based on aluminium alloys of 2124, 5083 and 6063 and reinforced by SiC particles were manufactured. Two different SiC sizes of 157 μm and 511 μm and two different extrusion ratios of 13.63:1 and 19.63:1 were used. The results of instrumented impact tests were compared with the microstructural and fractographic observations. The failure mechanisms and deformation behaviour of unreinforced alloys and composites were assessed. The impact behaviour of composites was affected by clustering of particles, particle cracking and weak matrix-reinforcement bonding. Agglomeration of particles reduced the impact strength of Al 2124 and 6063 based composites. Alumınum 6063 alloys and composites showed a better impact strength. The impact strength of 6063 composites increased with particle size and extrusion ratio. The effects of the test temperature on the impact behaviour of all materials were not very significant.     

SiC/Mo-Si复合涂层C/SiC复合材料的氧化性能

采用化学气相沉积法(CVD)和刷涂法在C/SiC复合材料表面制备抗氧化涂层。该涂层由致密的CVDSiC层和多孔的Mo-Si层交替组成,其结构从里到外为:CVDSiC层→Mo-Si层→CVDSiC层→Mo-Si层→CVDSiC层。涂层试样于1400℃的氧化实验和1400℃100℃的热震实验结果表明:在氧化和热震过程中,涂层均保持完整,没有出现脱落和掉块等失效现象。经1400℃、150h氧化后,涂层试样的失重率仅为0.25%,失重速率为6.61×10-6g.cm-.2h-1。在热震过程中,涂层试样基本保持氧化增重。经25次和50次热震后,涂层试样的弯曲强度保持率分别为95.73%和81.61%。SiC/Mo-Si复合涂层具有优异的抗氧化和抗热震性能,可对C/SiC复合材料提供1400℃、长时间的氧化防护。     

热固性SiC液体前驱体及其快速成型碳纤维/SiC复合材料

本文制备了一种液体热固性SiC前驱体（超支化聚碳硅烷,Tri-ImPCS,25℃黏度约为3 000 mPa·s）,并进行了高压模塑快速净成型碳纤维/SiC复合材料的工艺探索。液体环氧树脂RE1820（25℃黏度约为500 mPa·s）可以作为Tri-ImPCS的有效固化剂,在室温或较低加热温度（<100℃）固化定型;热固化后的Tri-ImPCS在进行无压烧结时没有发泡现象,能较好的维持形状。在N₂气氛中陶瓷化产率较高（以固化前驱体为基准,900℃陶瓷产率为74.8%）;Tri-ImPCS的C/Si原子比约为1.26,在微米尺度上C、Si等元素分布均匀。结合预浸料模压和高压注塑工艺,可以实现碳纤维/SiC复合材料坯体的快速致密。Tri-ImPCS是SiC陶瓷基复合材料理想的液态前驱体。      

Corrosion behaviour of aluminium matrix composites

Samples of aluminium alloy 2014 reinforced with 20–40 vol % of alumina or silicon carbide particles were tested by the potentiodynamic polarization technique. The chosen medium was 0.1m lithium perchlorate which tends to cause localized corrosion. The measurements revealed no impairment of the corrosion performance of the matrix alloy as a result of the presence of the reinforcement phase.     

Oxidation behaviour of mullite-SiC composites

The oxidation kinetics of three mullite-SiC composites were studied. The materials were all processed with the same amount of SiC, 10% by volume; in two of the composites the second phase was added as whiskers, and in the third as powders. The sintered composites were exposed to high temperatures (1200 to 1500 ° C) during variable time periods (maximum 122 h) under the oxidizing furnace atmosphere. The nature of the reaction layer formed has been analysed specifying the oxidation rate constants for each composite. The influence on the bend strength of the composites for one of the isothermal oxidizing treatments has also been measured.     

Oxidation effects during laser cladding of aluminium with SiC/Al powders

Aluminium substrates were covered with a layer of an Al-SiC powder mixture. The surface was scanned with a laser beam during which the surface was melted. The top layer of the laser tracks contained oxide plates apart from some large SiC particles. In the bottom layer a cellular network was found with aluminium cells and silicon-rich cell walls.     

涂敷含硼硅玻璃SiC涂层的C/SiC复合材料空气氧化行为

以2D C/SiC复合材料为基底, 采用聚合物裂解工艺(Polymer plyen)制备了含硼硅玻璃SiC自愈合涂层。利用扫描电镜对含硼硅玻璃SiC涂层的2D C/SiC复合材料氧化前后的微结构形貌进行了分析。研究了含硼硅玻璃SiC涂层的C/SiC复合材料在静态空气中700℃、 1000℃和1200℃下的氧化行为, 并分析了涂层层数对C/SiC复合材料氧化行为的影响。结果表明: 含硼硅玻璃SiC涂层在该温度下形成的玻璃相可以较好地封填表面缺陷(裂纹和孔洞); 并且随温度升高及涂层层数增加, 试样在氧化过程中质量减少率降低, 氧化后的强度保持率提高。      

Tensile fatigue behaviour of tightly woven carbon/carbon composites

The tensile fatigue behaviour of a tightly woven carbon/carbon composite was investigated as a function of stress level. Load-controlled fatigue tests were performed in tension-tension mode with a stress ratio, R, of 0.1 under ambient laboratory conditions. Results of composite behaviour are discussed in terms of the relationship of the stress/strain behaviour to the fatigue life of these composites as well as the effects of applied stress levels. It is shown that these composites exhibit good resistance to cyclic loading. No fatigue failures were obtained after 10⁶ cycles when the maximum tensile load in the fatigue cycle is less than or equal to 80% of the static tensile strength. Evidence of textural changes related to fatigue was observed in the matrix region of these composites.