Carbon Fiber Reinforced Silicon Carbide Research Articles

The Stability of the Coefficient of Friction and Wear Behavior of C/C–SiC

To develop a fundamental understanding of the tribological behavior of carbon fiber-reinforced silicon carbide (C/C–SiC) composites as brake pads and discs for high-speed trains, we have studied the brake friction properties of C/C–SiC composites at initial braking speeds ranging from 30 to 63 m/s. The friction mating pairs were fabricated by two methods to obtain composites of different SiC content. The composite with a SiC content of 40.3 % was used as the friction pad, and that with a SiC content of 85.6 % was used as the friction disc. In our experiments, an interesting turning point of 59 m/s was observed: the coefficient of friction (COF) decreased from 0.43 to 0.32 with increases in the braking speed from 30 to 49 m/s, at which braking speed it reached a plateau; the wear rate displayed a cubic curve against initial braking speed and reached a minimum of 315 mm3/MJ at 59 m/s. The topographical observations by scanning electron microscope combined with the residual stress analysis revealed that the limited number tribochemical layers, as well as the mismatch of thermal expansion coefficient between the carbon fiber and matrix, contribute to the unusual tribological characteristics of C/C–SiC composites. The experimental results suggest the good tribological potential of self-mated C/C–SiC composites in high-speed working conditions in terms of a steady COF and low wear rate.

Complete recovery of high temperature oxidation resistance in carbon fiber reinforced SiC composites by a recoating repair methodology

The current work reports on the oxidation behavior and residual flexural strength of carbon fiber–reinforced silicon carbide composites (C/SiC) after induction of thermal crack damage by heat treatment (HT) at 1900°C and the effect, therein, of a repair process involving recoating by SiC. As-prepared, heat-treated and heat-treated/recoated specimens, were subjected to static oxidation tests in air at a temperature range of 500–1500°C for 10h and then tested in three-point bending. It was found that composite weight of heat-treated samples decreased dramatically with increasing oxidation temperature with weight loss values of ~30% being systematically observed for oxidation temperatures above 800°C. On the other hand, as-prepared and heat-treated/SiC-recoated specimens reached almost their original weight after oxidation. The residual flexural strength of C/SiC composites with thermally-induced crack damage decreased significantly compared to as-prepared specimens, while SiC recoating was found to efficiently enable strength enhancement. Microstructural analysis showed that HT was associated with increased population and dimensions of micro-cracks on the C/SiC surface while SiC recoating enabled repair of HT-induced thermal crack damage hence leading to oxidation resistance recovery of the material.

Predictions of elastic property on 2.5D C/SiC composites based on numerical modeling and semi-analytical method

In this paper, the predictions of elastic constants of 2.5D (three-dimension angle-interlock woven) continue carbon fiber reinforced silicon carbide (C/SiC) composites are studied by means of theoretical model and numerical simulation. A semi-analytical method expressing elastic constants in terms of microstructure geometrical parameters and constitute properties has been proposed. First, both the geometrical model of the 2.5D composite and the representative volume element (RVE) in both micro- and meso-scale are proposed. Second, the effective elastic properties of the RVE in 2.5D C/SiC composites are obtained using finite element method (FEM) simulation based on energy equivalent principle. Finally, the remedied spatial stiffness average (RSSA) method is proposed to obtain more accurate elastic constants using nine correction factor functions determined by FEM simulations, also the effects of geometrical variables on mechanical properties in 2.5D C/SiC composites are analyzed. These results will play an important role in designing advanced C/SiC composites.

Predicting the mechanical behaviour of carbon fibre reinforced silicon carbide with interlaminar manufacturing defects

A finite element approach based on experimental material data is presented in order to compute the mechanical reliability of carbon fibre reinforced silicon carbide, C/C-SiC, taking interlaminar manufacturing defects into account. The approach is evaluated on sample scale by modelling the flexural behaviour of C/C-SiC samples containing delaminations after liquid silicon infiltration (LSI) processing. The non-destructive evaluation methods, determination of fracture mechanical input data and the numerical cohesive zone approach are described. The numerical predictions of flexural stiffness and strength of samples with and without interlaminar defects were validated by bending tests of the respective samples. The difference between tensile and bending behaviour is explained by FE modelling for this group of CMC materials.

The effect of Z-yarn density on the in-plane shear property of three-dimensional stitched carbon fiber reinforced silicon carbide composites

Abstract Three types of three-dimensional stitched carbon fiber reinforced silicon carbide composites (3DS C/SiCs) were fabricated by chemical vapor infiltration with the Z-yarn density of 4, 9, and 16 stitching/cm2 (S4, S9 and S16). The results showed: 3DS C/SiCs with different Z-yarn densities had identical damage mechanism which was referred to as rigid body sliding. The fracture surfaces of both S4 and S9 lied in the stitched line plane. However, S16 exhibited the fracture morphologies of plane rise. Compared with that of S4, the in-plane shear strengths of S9 and S16 increased by 13.1% and 37.5%, respectively. However, the shear moduli of them decreased by 22.2% and 36.4%. Benefitted from the studies of Turner, a formula was proposed to well predict the in-plane shear strength of 3DS C/SiCs with different Z-yarn density. Although they exhibited low in-plane shear strength, 3K 3DS C/SiCs would not alleviate the notch sensitivity through shear stress redistribution. However, the application of them with lower Z-yarn density should be avoided. The similar conclusions as listed above may be also attained for other Z-reinforced ceramic-matrix composites because 3DS C/SiC is a representative of them.

Mechanical properties of C–SiC composite materials fabricated by the Si–Cr alloy melt-infiltration method

Although carbon fiber-reinforced silicon carbide matrix composites fabricated using the liquid silicon infiltration method exhibit high thermal and oxidation resistances, their physical characteristics are limited because of the presence of unreacted, free Si within the materials. To resolve this problem, ingots prepared by alloying Cr with Si in ratios of 0, 5, 10, 25, and 50 at% were melted and made to infiltrate the composite, resulting in the formation of CrSi2 in the unreacted, free Si region without degrading the composite’s properties. The CrSi2 in the composite material reduced the amount of free Si and caused minimal variation in the flexural strength while significantly improving the fracture toughness of the composite. The results of scanning electron microscopy and transmission electron microscopy analyses indicated that the improvement in the fracture toughness was due to the presence of an amorphous interlayer between the Si and CrSi2 phases, as well as because of a stress field surrounding the CrSi2 phase.

Effect of Sintering Temperature on the Celsian/Yttrium Silicate Oxidation Resistant Coatings for C/SiC Composite

A novel celsian/yttrium silicate coating was deposited on carbon fiber reinforced silicon carbide matrix (C/SiC) composite, using BaO-Al2O3-SiO2 (BAS) glass andY2O3 powder as starting materials. The effects of sintering temperatures on microstructure and performance of coatings were studied. The results show that the final phases of sintered coatings are composed of celsian, yttrium silicate and remnant glass. The coating are dense, crack-free and pore-free in macroscopic scales when sintered at temperatures above 1400°C. The crystal grains in the coating grow too large, and the coating is loose in microstructure when sintered at temperatures higher than 1450°C. The coated samples sintered at 1450°C for 30min, which have the densest morphology and microstructure, have the lowest weight loss of 0.13 % after oxidation at 1500°C for 90 min.

Three-point bending test at extremely high temperature enhanced by real-time observation and measurement

We developed a three-point bending test equipment with a heating chamber to provide a high temperature environment. An observation window was intentionally opened in the chamber wall for image capture. A high speed camera is integrated to record the surface evolution of the specimen through the observation window. The fixture stage for the specimens was made of Al2O3 ceramic (>99% pure) and could resist extremely high temperature. This testing platform provides the specimens with an environment that is up to 1600°C in atmosphere for three-point bending test. Experiments were conducted for refractory alloy and C/SiC (carbon fiber reinforced silicon carbide composites) and the surface evolution of these specimens at high temperature was recorded. The crack propagation of the specimens was captured real-time and provided more detailed information for study of fracture behavior of the materials at high temperature.

The effects of Z-stitching density on thermophysical properties of plain woven carbon fiber reinforced silicon carbide composites

Three types of plain woven carbon fiber reinforced silicon carbide composites (C/SiCs) with 4, 9, and 16 Z-stitching/cm2 densities (S4, S9 and S16) were fabricated by chemical vapor infiltration. The results indicated that the activation energies for thermal diffusive mechanism transition of S9 and S16 increased by 151 and 192% compared with that of S4, respectively. With the increase of Z-stitching density, the positive effects of “pore” phase, in-plane fibers and Z-yarns on thermal conductivity were enhanced. Compared with that of S4, the through-thickness thermal conductivities of S9 and S16 increased by approximately 0.3 and 0.5W/m°C in the temperature range 200–1400°C, respectively. The thermal expansions of these composites were mainly determined by SiC matrix. The increase of structural integrity and decrease of SiC amount reduced the in-plane coefficient of thermal expansion (CTE) with the increase of Z-stitching. Compared with that of S4, the in-plane CTEs of S9 and S16 decreased by about 0.4 and 0.7×10−6°C−1 in the same temperature range, respectively.

Experimental Study on Ultrasonic Assisted Grinding of C/SiC Composites

In the present work, ultrasonic assisted grinding (UAG) and conventional grinding (CG, without ultrasonic) tests of Carbon fiber reinforced silicon carbide matrix (C/SiC) composites were conducted. In addition, analysis was done by comparing the machining quality, grinding force, and specific grinding energy between the two processes. The results showed that material removal mode of carbon fiber both in CG and UAG were brittle fracture, and fracture size had no obvious difference. Compared with CG, brittle fracture area of SiC increased during UAG. In comparison with CG, the normal grinding force and tangential grinding force for UAG were reduced maximally by 45%, 39% respectively of those for CG. Accordingly, specific grinding energy was also reduced by UAG. Therefore, UAG can improve the grinding performance of C/SiC composites significantly.

Microstructural analysis of a C/SiC ceramic based on the segmentation of X-ray phase contrast tomographic data

Abstract This paper is dedicated to the analysis of 3D data of carbon fiber reinforced silicon carbide ceramics. In the production process of C/SiC, a porous carbon preform reinforced with bundles of carbon fibers is infiltrated with liquid silicon at approximately 1 500 °C. The reaction between liquid silicon and carbon creates a layer of silicon carbide while the silicon vanishes almost completely. This material is able to withstand extremely high temperatures and it is extremely tough with respect to fracture. To increase the efficiency of the costly and time consuming production process, methods for monitoring the quality of the material are helpful. For instance, the thickness of the silicon carbide layer is a valuable measure. Moreover, due to different coefficients of thermal expansion of the components, typically cracks appear during the production process. For effective analysis 3D high resolution image data are necessary that can be acquired by synchrotron computed tomography. In a first image processing step, we segment the 3D image data with a convex optimization approach incorporating spatial regularity. Further, we work on the detection of cracks using an eigenvalue analysis of the 3D Hessian matrix determined in each pixel.

Experimental studies on drilling tool load and machining quality of C/SiC composites in rotary ultrasonic machining

Carbon fiber reinforced silicon carbide matrix (C/SiC) composites have great potential in space applications because of their excellent properties such as low density, superior wear resistance and high temperature resistance. However, the use of C/SiC has been hindered seriously because of its poor machining characteristics. With an objective to improve the machining process of C/SiC composites, rotary ultrasonic machining (RUM) and conventional drilling (CD) tests with a diamond core drill were conducted. The effects of ultrasonic vibration on mechanical load and machining quality were studied by comparing the drilling force, torque, quality of holes exit and surface roughness of drilled holes between the two processes. The results showed that the drilling force and torque for RUM were reduced by 23% and 47.6%, respectively of those for CD. In addition, the reduction in drilling force and torque decreased gradually with increasing spindle speed, while they changed slightly with increasing feed rate. Under identical conditions, RUM gave better holes exit than CD. Moreover, because of the lower lamellar brittle fracture and pit originating from carbon fibers fracture, the roughness of surface of drilled holes obtained with RUM was lower than CD and the maximum reduction was 23%.

Effect of PyC interphase thickness on mechanical behaviors of SiBC matrix modified C/SiC composites fabricated by reactive melt infiltration

A dense carbon fiber reinforced silicon carbide matrix composites modified by SiBC matrix (C/SiC-SiBC) was prepared by a joint process of chemical vapor infiltration, slurry infiltration and liquid silicon infiltration. The effects of pyrolytic carbon (PyC) interphase thickness on mechanical properties and oxidation behaviors of C/SiC-SiBC composites were evaluated. The results showed that C/SiC-SiBC composites with an optimal PyC interphase thickness of 450nm exhibited flexural strength of 412MPa and fracture toughness of 24MPam1/2, which obtained 235% and 300% improvement compared with the one with 50nm-thick PyC interphase. The enhanced mechanical properties of C/SiC-SiBC composites with the increase of interphase thickness was due to the weakened interfacial bonding strength and the decrease of matrix micro-crack amount associated with the reduction of thermal residual stress. With the decrease in matrix porosity and micro-crack density, C/SiC-SiBC composites with 450nm-thick interphase exhibited excellent oxidation resistance. The residual flexural strength after oxidized at 800, 1000 and 1200°C in air for 10h was 490, 500 and 480MPa, which increased by 206%, 130% and 108% compared with those of C/SiC composites.

Strength and toughness improvement in a C/SiC composite reinforced with slurry-prone SiC whiskers

The present paper reports on the strength and toughness improvement in carbon-fiber reinforced silicon carbide (C/SiC) composites as a result of slurry-prone SiC whisker presence at varying concentrations. For whisker contents of 5 and 15wt%, the SiCw–C/SiC composite flexural strength was found to increase by 98.5% and 64.3%, respectively, from the whisker-free case while work of fracture increased by 209.8% and 179.0%, respectively. For the same respective whisker concentrations, porosity was found to decrease by 4.9% and increase by 19.4% compared to plain samples. The composites’ interlaminar shear strength exhibited similar non-monotonic response with the property value for 5wt% whisker-reinforced composites being higher by 12.5MPa than the plain specimens and higher by 14.9MPa than the composites with 15wt% whisker content. Fiber pullout in SiCw–C/SiC composites was considerably more prominent than in the whisker-free material and the corresponding mean pullout lengths were significantly longer than in plain specimens. The improvements in strength and toughness were attributed to the energy dissipation mechanisms of crack deflection, whisker bridging and pullout coupled with conventional fiber pullout.

An Innovative Joint Structure for Brazing Cf/SiC Composite to Titanium Alloy

In view of aerospace applications, an innovative structure for joining a Ti alloy to carbon fiber reinforced silicon carbide has been developed. This is based on the perforation of the CMC material, and this procedure results in six-fold increase of the shear strength of the joint compared to the unprocessed CMC. The joint is manufactured using the active brazing technique and TiCuAg as filler metal. Sound joints without defects are produced and excellent wetting of both the composite ceramic and the metal is observed. The mechanical shear tests show that failure occurs always within the ceramic material and not at the joint. At the CMC/filler, Ti from the filler metal interacts with the SiC matrix to form carbides and silicides. In the middle of the filler region depletion of Ti and formation of Ag and Cu rich regions are observed. At the filler/Ti alloy interface, a layered structure of the filler and Ti alloy metallic elements is formed. For the perforation to have a significant effect on the improvement of the shear strength of the joint appropriate geometry is required.

Honeycomb Sandwich Structure of C<sub>f</sub>/SiC Ceramic Matrix Composites Prepared by PIP-CVI

continuous carbon fiber reinforced silicon carbide (Cf/SiC) ceramic matrix composites were prepared by precursor infiltration pyrolysis and chemical vapor infiltration (PIP-CVI process), in which the honeycomb sandwich structure preforms were fabricated by the three dimensional braid method. In this paper, the microstructure and the bending strength were observed and analyzed by SEM and three point bending method. The results of the study show that: The Cf/SiC ceramic matrix composites, which were lightweight and high strength, were prepared by that technique. The composite samples have a fiber volume fraction of 20%, a density of 0.38 g/cm3 and a flexural strength of 3.81 MPa. The honeycomb sandwich fiber reinforced ceramic matrix composite with a light weight, corrosion resistance and excellent physical and mechanical properties is a kind of structure and functional ceramic materials, which can realize the structure and the requirement of heat integration.

Oxidation Resistant Behaviour of Mullite/Yttrium Silicate Multilayer Coating for C/SiC Composites at 1500°C

Continuous carbon fibre reinforced silicon carbide (C/SiC) composites were fabricated by precursor infiltration and pyrolysis (PIP) process, a mullite/yttrium silicate multilayer coating was prepared by plasma spray method as the oxidation protective coating. The efficiency of the coating against oxidation was characterized by means of heat treatment of the C/SiC composites at 1500 °C in static air for 1 hour. The results indicated that the weight loss of the coated composites was only 3.4 %, and the flexural strength of the composites retained 95.3 % of the original strength.

In situ observation and measurement of composites subjected to extremely high temperature

In this work, we develop an instrument to study the ablation and oxidation process of materials such as C/SiC (carbon fiber reinforced silicon carbide composites) and ultra-high temperature ceramic in extremely high temperature environment. The instrument is integrated with high speed cameras with filtering lens, infrared thermometers and water vapor generator for image capture, temperature measurement, and humid atmosphere, respectively. The ablation process and thermal shock as well as the temperature on both sides of the specimen can be in situ monitored. The results show clearly the dynamic ablation and liquid oxide flowing. In addition, we develop an algorithm for the post-processing of the captured images to obtain the deformation of the specimens, in order to better understand the behavior of the specimen subjected to high temperature.

Interlaminar shear fatigue of a two-dimensional carbon fibre reinforced silicon carbide composite

Interlaminar shear fatigue properties of a two-dimensional carbon fibre reinforced silicon carbide composite were investigated at room temperature (RT) and 900°C in air. The interlaminar shear strength (ILSS) of the survived specimens was determined to reveal the damage mechanisms. The composite presents excellent resistance to the fatigue at RT. The fatigue limits at 900°C are much lower than that at RT. Moreover, ILSS can be enhanced for the survived composite to some extent. The damage involves the matrix cracking and interfacial debonding. Such damage offers the channels for the oxidation of the pyrolytic carbon interface and carbon fibres, and leads to the decrease in the fatigue limits at 900°C.

Micromechanics modeling for fatigue damage analysis designed for fabric reinforced ceramic matrix composites

A micromechanics analysis modeling method was developed to analyze the damage progression and fatigue failure of fabric reinforced composite structures, especially for the brittle ceramic matrix material composites. A repeating unit cell concept of fabric reinforced composites was used to represent the global composite structure. The thermal and mechanical properties of the repeating unit cell were considered as the same as those of the global composite structure. The three-phase micromechanics, the shear-lag, and the continuum fracture mechanics models were integrated with a statistical model in the repeating unit cell to predict the progressive damages and fatigue life of the composite structures. The global structure failure was defined as the loss of loading capability of the repeating unit cell, which depends on the stiffness reduction due to material slice failures and nonlinear material properties in the repeating unit cell. The present methodology is demonstrated with the analysis results evaluated through the experimental test performed with carbon fiber reinforced silicon carbide matrix plain weave composite specimens.