Liquid Silicon Infiltration Process Research Articles

Preparation and Properties of C/SiC Composites via Liquid Silicon Infiltration Process

Three-dimensional short carbon fiber felt reinforced C/SiC composites were prepared by the liquid silicon infiltration (LSI) process. The influences of different porosity ratios, carbon coating, and heat treatment of C/C substrates, on the properties of C/SiC composites were studied. The optimized porosity ratio is calculated as 40.1% when the volume percent of carbon fiber (including carbon coating) is 23%, and after screening porosity ratio from ~55% to ~20%, the optimized experimental result (39.5%) is highly in accordance with the design value. The C/SiC composite after process parameter optimization, has a flexural strength and modulus of 125 MPa and 120 GPa, respectively. The C/SiC composite without carbon coating has a flexural strength of only 77 MPa, showing carbon coating plays a key role. The heat treatment of C/C substrate at 1600°C also improves the flexural strength of C/SiC composite for nearly 50%, and porosity rearrangement and interface weakening are believed to contribute such improvement.

Effect of Braking Speed on Frictional Properties of Short Fiber C/C-SiC Brake Materials and Grey Cast Iron

Short fiber C/C-SiC brake materials were prepared by dipping the fibers in resin, chopping, warm pressing, and pyrolyzing, followed by a liquid silicon infiltration process. The effect of braking speed (initial braking speed) on the frictional properties of a pair of short fiber C/C-SiC brake materials and grey cast iron (HT250) (C/C-SiC-HT250) was investigated. The results indicated that the average friction coefficient of the C/C-SiC-HT250 increased to the maximum value at 10 m/s and then decreased with an increase in braking speed. The wear rate of the C/C-SiC increased with increasing braking speed when it was lower than 10 m/s and decreased when it was higher than 10 m/s. The wear was the result of the brittle fracture of asperities when the braking speed was lower than 10 m/s and induced granular debris. The wear for the tough cutting by C/C-SiC asperities or hard phase when the braking speed was higher than 10 m/s and resulted in ribbon debris. When the braking speed was higher than 20 m/s, the texture of the friction surface of the HT250 changed, which would affect the tribological properties.

Development of a numerical mesoscale material model for short fibre-reinforced ceramics matrix composites

The article describes the development of a numerical material model of ceramic matrix composite (CMC) reinforced by bundles of thousands of short carbon fibres and produced by means of a liquid silicon infiltration process. The objective of the article is the development of a numerical mesoscale model that considers the material as a simple bi-phasic composite constituted by an isotropic matrix with differently sized inclusions. The distinctive material microstructure that complicates the development of such a model is presented and the issues represented by the generation of the finite element models and by the identification of the effective properties of the constituent phases are discussed. In the presented approach, models are generated by numerically simulating the packing of bundles and phases are identified by means of tests and numerical analyses, which are performed on long fibre-reinforced specimens and on specimens subjected to a thermal process for the elimination of carbon reinforcement. The approach is applied to find out the parameters of a homogenized orthotropic model for CMC plates. The obtained results show that the numerical packing simulations can generate models with a realistic distribution of size, shape and orientation of the bundles. The mesoscale model and the phase properties identified by the proposed numerical and experimental procedure are validated by considering the stiffness of standard CMC specimens obtained in three-point bending tests. According to the results, the developed methodologies can be considered as a promising approach for a reliable prediction of short fibre-reinforced CMC elastic properties.

Wear-mechanical properties of filler-added liquid silicon infiltration C/C–SiC composites

A carbon fiber reinforced silicon carbide matrix (C/C–SiC) composites material was manufactured by introducing a filler into the liquid silicon infiltration (LSI) process. The filler consisted of Si:Carbon black=1:1 mixed with a phenol resin. Use of the filler resulted in a negligible reduction in the residual free Si of approximately 0.7% but increased 15% of reacted SiC amount. Dilatometer and X-ray diffraction (XRD) evaluations also confirmed improved formation of reaction-bonded silicon carbide (SiC) in the matrix. The wear rate was decreased more than 2.5-fold, indicating significantly improved wear-resistance properties. However, flexural strength gradually decreased and fiber damage was observed in fracture surface with increases in filler content.

Reaction Formed SiC Prepared by Room Temperature Freezing Casting

The porous carbon preforms with fine pore structure has been successfully fabricated by room temperature freezing casting, and the reaction formed SiC with fine mechanical property has prepared successfully by liquid silicon infiltration process. Charcoal powder was used as carbon resource, camphene was used as sublimate vehicle, methyl cellulose was used as pore maker and bonder. The result shows that the homogeneity of the porous carbon preform has been improved largely by adding methyl cellulose ,and the defects of reaction formed silicon carbide has reduced largely also. The density, average flexural strength and Weibull modulus of the best reaction formed silicon carbide prepared in this paper is 2.86 g/cm3, 430.75MPa and 9.29 respectively.

Fabrication of biomorphic SiC composites using wood preforms with different structures

Biomorphic SiC composites were fabricated from wood, including high-density compressed cedar, high-density fiberboard (HDF) and low-density paulownia followed by the fabrication of a preform and liquid silicon infiltration (LSI) process. The degree of molten silicon infiltration was strongly dependent on the cell wall thickness and pore size of the carbon preform. The mechanical properties of the biomorphic SiC composites were characterized by compressive tests at room temperature, 1000°C and 1200°C, and the relationship between the mechanical properties and the microstructural characteristics was analyzed. The compressive strength of the biomorphic composites was found to be strongly dependent on their bulk density and decreased as the test temperature increased to 1200°C. Strength reduction in the biomorphic SiC composites occurred due to the deformation of the remaining Si at elevated temperatures under ambient atmospheric conditions.

Fabrication of C/SiC composites by combining liquid infiltration process and spark plasma sintering technique

Carbon fibre-reinforced silicon carbide composites (C-SiC) were fabricated combining, for the first time, a liquid infiltration process (LI) of a mesophase pitch doped with silicon carbide nanoparticles followed by reactive liquid silicon infiltration using Spark Plasma Sintering (SPS) technique. A graphitization step was applied in order to improve the effectiveness of the processing. Up to three different morphologies of SiC particles were identified with a noticeable influence on the preliminary oxidation tests carried out. The presence of SiC nanoparticles added to the carbon matrix affects the morphology of the SiC obtained by in situ reaction of silicon and carbon during the LI process by SPS and it leads to an improvement of the material oxidation resistance. The results show that SPS is a promising method to develop C-SiC composites in a short time and with a high efficiency in the liquid silicon infiltration process.

서로 다른 밀도를 갖는 탄소섬유강화 탄화규소 복합재료의 압흔응력에 의한 기계적 거동

In this study, we investigated the mechanical behavior of carbon fiber reinforced silicon carbide composites by indentation stress. Relatively porous and dense fiber reinforced ceramic composites were fabricated by liquid silicon infiltration (LSI) process. Densification of fiber composite was controlled by hardening temperature of preform and consecutive LSI process. Load-displacement curves were obtained during indentation of WC sphere on the carbon fiber reinforced silicon carbide composites. The indentation damages at various loads were observed, and the elastic modulus were predicted from unloading curve of load-displacement curve.

Tribological Properties of Short Fiber C/SiC Brake Materials and 30CrSiMoVA Mate

In this study, the short fiber C/SiC brake materials were prepared by a combined process of the fibers dipped with resin, chopping, warm pressing, pyrolyzing, and the liquid silicon infiltration process. The tribological properties of short fiber C/SiC brake materials and 30CrSiMoVA mate were investigated. The results indicated that the average friction coefficient decreased with the increase of braking speed (initial braking speed), and the friction coefficient tended to be constant when the braking speed was higher than 20 m/s. The braking was stable when the braking speed was 5 m/s, and the braking was unstable when the braking speed was higher than 10 m/s. The wear rate of the C/SiC increased with the increase of braking speed when the braking speed was less than 10 m/s, decreased with the increase of braking speed when the braking speed was less than 20 m/s, and then increased afterward with the increase of braking speed. When the braking speed was higher than 20 m/s, an oxidation-abrasion mechanism could occur. With braking speed increasing, the number of the ribbon debris increased, and the ribbon debris got long and thick, and the number of big granular debris increased.

Microstructure and frictional properties of C/SiC brake materials with sandwich structure

C/SiC brake materials with a sandwich structure were prepared by three step process, chemical vapor infiltration, slurry infiltration and liquid silicon infiltration process. The fabricated brake materials consist of a C-fiber rich main body and two SiC-rich frictional layers on the surface. The microstructure and frictional properties of C/SiC brake materials were investigated. The results indicated that the density and open porosity of the materials were 2.2 g/cm 3 and 4%, respectively. The phase distribution in the friction layers of C/SiC with sandwich structure was homogeneous, and the silicon was little and dispersed in the friction functional layers. The joining region between friction functional layer and mechanical functional layer has an inter-laminar shear strength of about 27 ± 9 MPa, indicating its reliability. The frictional properties under wet condition of the C/SiC with the sandwich structure showed no fading, and were better than that of the 3D needled C/SiC. The static friction coefficient and linear wear rate of the C/SiC with the sandwich structure was higher than that of the 3D needled C/SiC. The C/SiC brake materials with sandwich structure would have higher brake efficiency.

Microstructure and frictional properties of 3D needled C/SiC brake materials modified with graphite

The 3D needled C/SiC brake materials modified with graphite were prepared by a combined process of the chemical vapor infiltration, slurry infiltration and liquid silicon infiltration process. The microstructure and frictional properties of the brake materials were investigated. The density and open porosity of the materials as-received were about (2.1±0.1) g/cm 3 and (5±1)%, respectively. The brake materials were composed of 59% C, 39% SiC, and 2% Si (mass fraction). The content of Si in the C/SiC brake materials modified with graphite was far less than that in the C/SiC brake materials without being modified with graphite, and the Si was dispersed. The braking curve of the 3D needled C/SiC modified with graphite was smooth, which can ensure the smooth and comfortable braking. The frictional properties under wet condition of the 3D needled C/SiC modified with graphite showed no fading. And the linear wear rate of the C/SiC modified with graphite was lower than that of the C/SiC unmodified.

Effect of pyrocarbon content on thermal and frictional properties in C/C preforms of C/C–SiC composites

This paper concerns the influence of the phase composition (SiC, Si, and pyrocarbon) modification in the C/C–SiC composite on the thermal and friction behavior, and the related mechanisms. For this purpose, four different C/C–SiC composites with the same fiber volume but different phase contents were prepared by chemical vapor infiltration, combining with liquid silicon infiltration process, and these samples were submitted to structural and thermal characterization, then to friction and wear tests using a disk-on-disk configuration at the same condition. As a result, the composition and phase content of the C/C–SiC composites play an important role in varying thermal conductivity, wear mechanism and wear rate. The C/C–SiC composite with higher pyrocarbon content and less ceramic content showed higher transverse thermal conductivity. The friction coefficients increased with increasing SiC and Si content. The wear mechanism changed from an abrasive action to an adhesive action with increasing the Si content.

Microstructure, Thermophysical, and Ablative Performances of a 3D Needled C/C–SiC Composite

The microstructure, thermophysical, and ablative properties of a 3D needled C/C–SiC composite fabricated by chemical vapor infiltration combined with the liquid silicon infiltration process were investigated. The composite was composed of 64 wt% C, 20 wt% SiC, and 16 wt% Si. The thermal diffusivity in the plane direction was much higher than that in the through‐the‐thickness direction, while it was reversed for the coefficients of thermal expansion, and the differences reduced with increasing temperature. The linear and mass ablation rates in the oxyacetylene flame were 0.0039 mm/s and 0.0016 g/s on average, respectively. Various ablation processes including sublimation, thermochemical denudation, and oxidations occurred in different sections.

Mechanical and Tribological Properties of 3D Carbon Fiber Reinforced SiC Composites Prepared by Liquid Silicon Infiltration

C/SiC composites were prepared by liquid silicon infiltration process, and their microstructure, mechanical and tribological properties were studied in this paper. The results showed that the composites demonstrated non-catastrophic fracture behavior with long fibers pulled out and about 115 MPa flexural strength. The stability of coefficient of friction (COF) was improved and wear rate demonstrated a linear variation with the increasing of rotation speeds. However, wear rate exhibited a higher value (~3.6 μg/m) under a higher load (~150 N), even though the COF curves for C/SiC composites showed no significant changes.

The carbon black effect on crack formation during pyrolysis step in liquid silicon infiltration process for Cf/C-SiC composites

The formation of crack patterns during the pyrolysis step, which converts the carbon fiber-reinforced plastic composite (CFRP) to a Cf/C composite as one step in the liquid silicon infiltration (LSI) process, was investigated. Generally, cracks occur as a result of variances in thermal shrinkage between the matrix and the fiber during pyrolysis. The addition of carbon black powder as a filler resulted in a reduction in the shrinkage, but more cracks were formed. The transversal crack increased, and the partial delamination was newly occurred as the filler was increased. The properties of the matrices also changed; the fracture toughness decreased, and the void area increased. Consequently, the crack formation occurs not only by the thermal shrinkage difference between fiber and matrix but also the effect of matrix fracture toughness or void content. The flexural strength of LSI-processed samples was also measured, and the filler improved the mechanical strength but reduced its reliability.

Friction and Wear Properties of 3D Carbon/Silicon Carbide Composites Prepared by Liquid Silicon Infiltration

Carbon/silicon carbide (C/SiC) composites were prepared by a liquid silicon infiltration (LSI) process and their microstructure and friction and wear properties studied. The matrices of the C/C green bodies were found to be reinforced with dense carbon fiber bundles hanging together. The density of the composites before and after the LSI process was 1.25 and 1.94 g/cm3, respectively. However, the open porosity of C/SiC composites was about 16% due to the opening of closed pores during the machining process. The C/SiC composites exhibited excellent tribological properties in the dry condition, with an average coefficient of friction (COF) and wear rate of about 0.29 and 16.15 μg/m MPa, respectively. In comparison, the average COF was about 0.13 in the moist condition, with a wear rate of 5.87 μg/m MPa. The main wear mechanism of the C/SiC composites was worn particles and debris with a high degree of hardness, producing a plough effect on the friction surface in the dry condition and an adhesive effect in the moist condition.

Preparation of C/C-SiC Brake Materials with Low Cost and High Friction Performance

C/C-SiC brake materials were prepared by improved chemical liquid vaporized infiltration (CLVI) combined with liquid silicon infiltration (LSI) process, which needed less than thirty hours. The microstructure and frictional properties of the material were investigated. The density and porosity of the C/C-SiC brake material were 2.05 g/cm3 and 4.8%, respectively. The average dynamic friction coefficient of the materials was about 0.36, and the friction coefficient was stable. The average linear wear rate was less than 4.7 µm cycle-1 for rotating and stationary disk. The matrix composition and microstructure resulted in the high frictional performances.

Effect of pyrocarbon content in C/C preforms on microstructure and mechanical properties of the C/C–SiC composites

Carbon fiber reinforced silicon carbide matrix (C/C–SiC) composites were prepared by liquid silicon infiltration (LSI) process, using four kinds of quasi-three-dimensional C/C preforms with the same fiber volume fraction (32%) but different pyrocarbon content (from ∼20% to ∼50%, in volume) filled by chemical vapor infiltration (CVI). The microstructure and mechanical properties of C/C–SiC composites have been investigated. X-ray diffractmeter (XRD) analysis results show the composites are composed of three phases of β-SiC, C and Si. With the increase of the pyrocarbon content in the C/C preforms, the content of formed silicon carbide in the C/C–SiC composites decreases but the residual pyrocarbon increases. Mechanical tests were performed to assess the role of the matrix and phase composition in the C/C–SiC composites. The results demonstrate that the flexural strength and shear strength of the composites increase gradually as the increase of the content of residual pyrocarbon. The flexural and shear strength of the C/C–SiC composite produced of the C/C preform with pyrocarbon content of ∼42 vol.% reached the highest value.

탄소섬유 배열이 LSI Cf-Si-SiC 복합체의 특성에 미치는 영향

Carbon fiber fabric-silicon carbide composites were fabricated by liquid silicon infiltration (LSI) process. The porous twodimensional carbon fiber fabric performs were prepared by 13 plies of 2D-plain-weave fabric in a three laminating method, [0/90], [±45], [0/90/±45] lay-up, respectively. Before laminating, a thin pyrolytic carbon (PyC) layer deposited on the surface of 2D-plain weave fabric sheets as interfacial layer with C₃H? and N₂ gas at 900℃. A densification of the preforms for Cf-Si-SiC matrix composite was achieved according to the LSI process at 1650℃ for 30 min. in vacuum atmosphere. The bending strength of the each composite were measured and the microstructural consideration was performed by a FE-SEM.

Carbon/Carbon–Silicon-Carbide Dual-Matrix Composites for Brake Discs

Composite ceramic materials reinforced with carbon fibers are interesting materials because of their excellent mechanical and thermo-physical properties, which make them appropriate for many applications, including re-entry shields, rocket nozzles, disc brakes, and prosthetic devices. For all these purposes, many different types of such materials have been developed, for example, carbon/silicon-carbide or carbon/carbon–silicon-carbide composites that are commonly produced from carbon/carbon composites impregnated with liquid silicon by the liquid-silicon infiltration (LSI) process. In this work, a new ceramic matrix composite friction material for brake discs was developed that combines a high fracture toughness with good oxidation and abrasion resistance, good thermal conductivity, and the appropriate friction characteristics. For the production of such materials, the “dual-matrix” approach combined with reactive sintering was used. The materials have suitable mechanical properties and the braking discs have appropriate coefficient of friction and very low wear rate.