Design,Preparation and Properties of Carbon Fiber Reinforced Ultra-High Temperature Ceramic Composites for Aerospace Applications:A Review

Carbon fiber reinforced ultra-high temperature ceramic(UHTC) composites, consisting of carbon fibers embedded in a UHTC-matrix or a C–SiC–UHTC-matrix, are deemed as the most viable class of materials that can overcome the poor fracture toughness and thermal shock resistance of monolithic UHTC materials, and also improve the oxidation resistance and ablation resistance of C/C and C/SiC composites at ultra-high temperatures. In this review, we summarize the different processing routes of the composites based on the UHTC introducing methods, including chemical vapor infiltration/deposition(CVI/D),precursor infiltration and pyrolysis(PIP), reactive melt infiltration(RMI), slurry infiltration(SI), in-situ reaction, hot pressing(HP), etc; and the advantages and drawbacks of each method are briefly discussed. The carbon fiber reinforced UHTC composites can be highly tailorable materials in terms of fiber,interface, and matrix. From the perspective of service environmental applications for engine propulsions and hypersonic vehicles, the material designs(mainly focusing on the composition, quantity, structure of matrix, as well as the architecture of carbon fibers, UHTCs and pores), their relevant processing routes and properties(emphasizing on the mechanical and ablation properties) are discussed in this paper. In addition, we propose a material architecture to realize the multi-function through changing the distribution of carbon fibers, UHTCs and pores, which will be an important issue for future development of carbon fiber reinforced UHTC composites.     

Compressive Creep Behavior of TiC/AZ91D Magnesium-matrix Composites with Interpenetrating Networks

The 42.1 vol. pct TiC/AZ91D magnesium-matrix composites with interpenetrating networks were fabricated by in-situ reactive infiltration process. The compressive creep behavior of as-synthesized composites was investigated at temperature ranging from 673 to 723 K under loads of 95-108 MPa. For a comparative purpose,the creep behavior of the monolithic matrix alloy AZ91D was also conducted under loads of 15-55 MPa at 548-598 K. The creep mechanisms were theoretically analyzed based on the power-law relation. The results showed that the creep rates of both TiC/AZ91D composites and AZ91D alloy increase with increasing the temperature and load. The TiC/AZ91D composites possess superior creep resistance as compared with the AZ91D alloy. At deformation temperature below 573 K, the stress exponent n of AZ91D alloy approaches theoretical value of 5, which suggests that the creep process is controlled by dislocation climb. At 598 K, the stress exponentof AZ91D is close to 3, in which viscous non-basal slip deformation plays a key role in the process of creep deformation. However, the case differs from that of AZ91D alloy when the stress exponent n of TiC/AZ91D composites exceeds 9, which shows that there exists threshold stress in the creep process of the composites, similar to other types of composites. The average activation energies for the creep of the AZ91D alloy and TiC/AZ91D composites were calculated to be 144 and 152 k J/mol, respectively. The existence of threshold stress in the creep process of the composites leads to an increase in activation energy for creep.     

Mechanical Property,Oxidation and Ablation Resistance of C/C–ZrB_2–ZrC–SiC Composite Fabricated by Polymer Infiltration and Pyrolysis with Preform of C_f/ZrB_2

C/C–ZrB_2–ZrC–SiC composites were fabricated by polymer infiltration and pyrolysis(PIP) with a preform of C_f/ZrB_2. The carbon fibers and the resin carbon were coated with ceramic layer after PIP in the composites. The composite presents a pseudo-plastic fracture due to deflection of cracks and pullout of fibers.The composite has a higher bending strength by this method in comparison with the conventional PIP process due to fewer heat treatment cycles. The static oxidation test shows that the mass loss of the composites is no more than 1% after 20 min oxidation at 1100 °C. The "core–shell" structure between ZrC–SiC ceramic and other phases plays a positive role in preventing the inward diffusion of oxygen. The ablation resistance of the C/C–ZrB_2–ZrC–SiC composite samples was tested using a plasma generator. After ablation for 120 s, the mass and linear ablation rates of the composites are 4.65 mg cm~(-2)s~(-1) and 2.46 μm s~(-1), respectively. The short carbon layer shows a better ablation resistance than the nonwoven carbon fabric layer after the ceramic coating is peeled off because of its higher ceramic content.     

Microstructure and Eutectic Transformation of Squeeze Casting Alumina／Zinc Alloy Composites

Alumina fiber-reinforced zinc alloy composites were manufactured by squeeze casting, and the eutectic transformation in the zinc alloy composites was studied. The results indicate that there is a fine and close interface between the fiber and the matrix,and the alloy elements can improve the combination between the fibers and the matrix in the composites. The fibers can serve as the sites of heterogeneous nucleation of the eutectic in the zinc alloy during the solidification of the composites, and the silicon on the interface between the fibers and the matrix plays a leading role during the coupled growth of the eutectic so that the eutectic transformation of the composites consists of Al-Si eutectic transformation and Zn-Al eutectic transformation.     

Processing and Performance of Alumina Fiber Reinforced Alumina Composites

Processing of alumina fiber-reinforced alumina matrix composites by hot-pressing was described. The mechanical properties of the composites fabricated by different sintering conditions including temperature and pressure have been investigated. The results indicated that the higher sintering temperature and pressure corresponded to the higher bulk density and higher maximum strength of the composite, whereas the pseudo-ductility of the composite was lower. The preliminary results of the composite with monazite-coated fibers showed that maximum strength could be improved up to 35% compared with the noncoated fiber composite in the same sintering condition. Moreover, the fracture behavior of the composite changed from completely brittle fracture to non-brittle fracture under the suitable sintering conditions. SEM observation of the fracture surface indicated that the coating worked as a protective barrier and avoided sintering of the fibers together even at high temperature and pressure during densification process.     

Carbon-Coated-Nylon-Fiber-Reinforced Cement Composites as an Intrinsically Smart Concrete for Damage Assessment during Dynamic Loading

Concrete containing short carbon-coated-nylon fibers (0.4～2.0 vol. pct) exhibited quasi-ductile response by developing a large damage zone prior to fracture localization. In the damage zone, the material was microcracked but continued to local strain-harden. The carbon-coated-nylon-fiber-reinforced concrete composites (NFRC) were found to be an intrinsically smart concrete that could sense elastic and inelastic deformation, as well as fracture. The fibers served to bridge the cracks and the carbon coating gave the conduction path. The signal provided came from the change in electrical resistance, which was reversible for elastic deformation and irreversible for inelastic deformation and fracture. The resistance decrease was due to the reduction of surface touch resistance between fiber and matrix and the crack closure. The resistance irreversible increase resulted from the crack opening and breakage of the carbon coating on nylon fiber.     

Microstructure and Mechanical Properties of C/C-ZrC-SiC Composites Fabricated by Reactive Melt Infiltration with Zr,Si Mixed Powders

To meet the increasing demand for advanced materials capable of operation over 2000℃for future thermal protection systems application,C/C—ZrC—SiC composites were fabricated by reactive melt infiltration(RMI) with Zr,Si mixed powders as raw materials.The structural evolution and formation mechanism of the C/C—ZrC -SiC composites were discussed,and the mechanical property of the as-prepared material was investigated by compression test.The results showed that after the RMI process,a special structure with ZrC-SiC multi-coating as outer layer and ZrC-SiC-PyC ceramics as inner matrix was formed.ZrC and SiC rich areas were formed in the composites and on the coating surface due to the formation of Zr-Si intermetallic compounds in the RMI process.Mechanical tests showed that the average compression strength of the C/C-ZrC-SiC composites was 133.86 MPa,and the carbon fibers in the composites were not seriously damaged after the RMI process.     

C/SiC Composites with a Self-healing SiBC Matrix Fabricated by Liquid Silicon Infiltration

正Most researched continuous carbon fiber reinforced silicon carbide matrix composites(C/Si C)composites have porous matrix,which are fabricated by chemical vapor infiltration(CVI)or polymer infiltration and pyrolysis(PIP).The porous C/Si C composites exhibit higher fracture toughness,     

Improvement on the Corrosion Resistance of AZ91D Magnesium Alloy by Aluminum Diffusion Coating

By combination of magnetron sputtering deposition and vacuum annealing, an aluminum diffusion coating was prepared on the substrate of AZ91D alloy to improve its corrosion resistance. The microstructure and composition of the diffusion coating was investigated by scanning electron microscopy and X-ray diffraction. The diffusion coating was mainly comprised of β phase-Al12Mg17. The continuous immersion test in 3.5 wt pct neutral NaCl solution indicated that the specimen with diffusion coating had better corrosion resistance compared with the bare AZ91D alloy specimen. The potentiodynamic polarization measurement indicated that the diffusion coating could function as an effectively protective layer to reduce the corrosion rate of AZ91D alloy when exposed to 3.5 wt pct NaCl solution.     

Simultaneously enhancing mechanical and tribological properties of carbon fiber composites by grafting SiC hexagonal nanopyramids for brake disk application

Extensive attention has been drawn to the development of carbon fiber composites for their application in brake disks due to the increasing demand for brake disks with high mechanical strength and better tribological properties. Herein, we design SiC hexagonal nanopyramids modified carbon/carbon(SiCNPsC/C) composites, in which SiCNPs are radially grafted on the carbon fibers by the combined sol-gel and carbothermal reduction method, and pyrolytic carbon(Py C) matrix is deposited on nucleation si...     

Selective growth of SiC nanowires in interlaminar matrix for improving in-plane strengths of laminated Carbon/Carbon composites

β-SiC nanowires(SiCNWs) were selectively grown in the interlaminar matrix with a volume fraction of0.65% by applying a pyrocarbon coating on carbon fibers, which realizes the proper reinforcement of C/C composites. The thickness of the pyrocarbon is optimized to 0.5 μm based on the analysis of in-situ fiber strengths with the fracture mirror method. The pyrocarbon coating increased the in-situ fiber strength by~7% and prevent brittle fracture of the composites. Compared with C/C, the interlaminar shear and flexural strength of SiCNW-C/C(10.06 MPa and 162.44 MPa) increase by 158% and 57%. Incorporating SiCNWs changes the crystallite orientations and refines the crystallite size of pyrocarbon matrix. The functions of SiCNWs vary with their loading density. When SiCNWs are sufficient in the matrix, they help reinforcing and improving the critical failure stress of the matrix. When their density decreases to a certain degree, SiCNWs help changing the crystallite orientations of pyrocarbon and toughening the matrix.     

Interfacial Interaction in Coated Carbon Fibre Reinforced Aluminous Mg-based Composites

Four kinds of Mg alloys reinforced with carbon fibres were fabricated by a gas pressure infiltration technique. The fibres were pre-coated a SiO2 layer prior to fabrication. DifFerent microstructures and interactions in the fibre-matrix interface of these composites were observed by transmission electron microscopy （TEM）. The results showed that the interracial interaction strongly depended on the content of Al in the Mg-based matrices. The microstructure of the interface could then be controlled by adjusting the Al content of the Mgbased matrix. In addition, fibres extracted from different Mg-based matrix all had some degradation owing to the interracial reaction and the fibre-matrix interdiffusion.     

Surface State of Carbon Fibers Modified by Electrochemical Oxidation

Surface of polyacrylonitrile (PAN)-based carbon fibers was modified by electrochemical oxidation. The modification effect on carbon fibers surface was explored using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Results showed that on the modified surface of carbon fibers, the carbon contents decreased by 9.7% and the oxygen and nitrogen contents increased by 53.8% and 7.5 times, respectively. The surface roughness and the hydroxyl and carbonyl contents also increased. The surface orientation index was reduced by 1.5% which decreased tensile strength of carbon fibers by 8.1%, and the microcrystalline dimension also decreased which increased the active sites of carbon fiber surface by 78%. The physical and chemical properties of carbon fibers surface were modified through the electrochemical oxidative method, which improved the cohesiveness between the fibers and resin matrix and increased the interlaminar shear strength (ILSS) of carbon fibers reinforc     

Ablative and Mechanical Properties of C/C—ZrC Composites Prepared by Precursor Infiltration and Pyrolysis Process

C/C-ZrC composites with continuous ZrC matrix were prepared by precursor infiltration and pyrolysis process using zirconium-containing polymer.Ablation properties of the composites were investigated by oxyacetylene flame with heat flux of 2380 and 4180 kW/m~2,respectively.The results showed that C/C-ZrC composites exhibited excellent ablation resistance under the heat flux of 2380 kW/m~2 for 120 s and a tree-coral-like ZrO_2protective layer formed after ablation.However,when the heat flux increased to 4180 kW/m~2,the maximum temperature of ablated surface reached 2500 ℃ and a strong degradation of ablation resistance was observed due to the weak bonding between the formed ZrO_2 layer and the composites.The flexural strength of C/C-ZrC composites was 110.7 ± 7.5 MPa.There were a large number of carbon fiber bundles pull-out,and the composites exhibited a pseudo-plastic fracture behavior.     

Thermo-physical Properties of Continuous Carbon Fiber Reinforced Copper Matrix Composites

Continuous carbon fiber reinforced copper matrix composites with 70％(volume fraction)of carbon fibers prepared by squeeze casting technique have been used for investigation of the coefficient of thermal expansion(CTE)and thermal conductivity．Thermo-physical properties have been measured in both, longitudinal and transversal directions to the fiber orientation．The results showed that Cf／Cu composites may be a suitable candidate for heat sinks because of its good thermo-physical properties e．g．the low CTE(4.18×10-6／K)in longitudinal orientation and(14．98×10-6／K)in transversal orientation at the range of 20-50℃，a good thermal conductivity(87．2 W／m·K)in longitudinal orientation and(58．2 W／m·K)in transversal orientation．Measured CTE and thermal conductivity values are compared with those predicted by several well-known models．Eshelby model gave better results for prediction of the CTE and thermal conductivity of the unidirectional composites．     

Mechanical Properties and Fracture Behavior of Mg-Al/AlN Composites with Different Particle Contents

In this study, magnesium matrix composites reinforced with different loading of AlN particles were fabricated by the powder metallurgy technique. The microstructure, bending strength and fracture behavior of the resulting Mg-Al/Al N composites were investigated. It showed that the 5 wt% AlN reinforcements led to the highest densification and bending strength. The total strengthening effect of AlN particles was predicted by considering the contributions of CTE mismatch between the matrix and the particles,load bearing and Hall–Petch mechanism. The results revealed that the increase of dislocation density,the change of Mg17Al12 phase morphology, and the effective load transfer were the major strengthening contributors to the composites. The fracture of the composites altered from plastic to brittle mode with increasing reinforcement content. The regions of clustered particles in the composites were easy to be damaged under external load, and the fracture occurred mainly along grain boundaries.     

SiCp/Al Composites Fabricated by Modified Squeeze Casting Technique

A cost effective method was introduced to fabricate pure aluminum matrix composites reinforced with 20% volume fraction of 3.5 μm SiC particles by squeeze casting followed by hot extrusion. In order to lower volume fraction of the composites, a mixed preform containing pure aluminum powder and the SiC particles was used. The suitable processing parameters for the infiltration of pure aluminum melt into the mixed preform are： melt temperature 800℃, preform temperature 500℃, infiltration pressure 5 MPa, and solidification pressure 50 MPa. Microstructure and properties of the composites in both as-cast and hot extruded states were investigated. The results indicate that hot extrusion can obviously improve the mechanical properties of the composite.     

Study on the Thermal Expansion and Thermal Cycling of AlNp／Al Composites

The AIN particle reinforced aluminum matrix composites with 50% volume fraction were fabricated by squeeze-casting technology.The thermal expansion behavior and its response to thermal cycling were studied between 20℃ and 400℃.Compared with four theoretical models,the measured CTEs of the composite lie within the elastic bounds derived by Schapery′s analysis .Schapery′s model and Kerner′s model agree well with the CTEs of the composites at lower temperature and elevated temperature,respectively.Strain hysteresis was observed between heating and cooling curves during cycling.This was attributed primarily to the anelastic behavior of the matrix induced by matrix residual stresses.     

Mechanical and electromagnetic wave absorption properties of C_f-Si_3N_4 ceramics with PyC/SiC interphases

Aiming to obtain microwave absorbing materials with excellent mechanical and microwave absorption properties, carbon fiber reinforced Si_3N_4 ceramics(Cf-Si_3N_4) with pyrolytic carbon(PyC)/SiC interphases were fabricated by gel casting. The influences of carbon fibers content on mechanical and microwave absorption properties of as-prepared Si_3N_4 based ceramics were investigated. Results show that chemical compatibility between carbon fibers and Si_3N_4 matrix in high temperature environment can be significantly improved after introduction of Py C/SiC interphases. As carbon fibers content increases from 0 to 4 wt%, flexural strength of Si_3N_4 based ceramics decreases slightly while fracture toughness obviously increases. Moreover, both the real and imaginary parts of complex permittivity increase with the rising of carbon fibers content within the frequency range of 8.2–12.4 GHz. Investigation of microwave absorption shows that the microwave attenuation ability of Cf-Si_3N_4 ceramics with Py C/SiC interphases is remarkably enhanced compared with pure Si_3N_4 ceramics. Effective absorption bandwidth(-10 d B) of10.17–12.4 GHz and the minimum reflection less of-19.6 d B are obtained for Si_3N_4 ceramics with 4 wt%carbon fibers in 2.0 mm thickness. Cf-Si_3N_4 ceramics with Py C/SiC interphases are promising candidates for microwave absorbing materials with favorable mechanical property.     

Preparation and Corrosion Resistance of Magnesium Coatings by Magnetron Sputtering Deposition

Magnesium coatings were fabricated on stainless steel substrates (1Cr11Ni2W2MoV) by a plane magnetron sputtering technique. The argon pressure and the substrate condition (including temperature and the substrate was rotated or fixed) were varied in order to evaluate the influence of the parameters on the crystal orientation and morphology of the coating. The corrosion behavior of the coatings in 1 wt pct NaCl solution was studied by electrochemical methods.The results showed that all coatings exhibited preferred orientation (002) as the argon pressure increased from 0.2 to 0.4 Pa. The morphologies of the coatings varied with the argon pressure and with whether the substrate was rotated or fixed. The open circuit potential of the coatings was more positive than that of cast AZ91D magnesium alloy.However, the immersion test in 1 wt pct NaCI solution showed that the corrosion rates of the coatings were higher than that of cast AZ91D magnesium alloy.