Fiber-reinforced SiC Matrix Composites Research Articles

The synergetic effect of He and Kr irradiation on helium bubble evolution in SiC/SiC composite: Combining in-situ TEM observation with MD simulation

SiC fiber reinforced SiC matrix composites (SiC/SiC composites) are considered as one of the promising structural materials for liquid type breeding blanket in the fusion energy system. The transmutation gas production rate in fusion reactor is significantly higher compared with fission reactors. An innovative method combining in-situ irradiation and TEM observation and MD simulation was utilized to evaluate the synergetic effects of helium and irradiation on SiC/SiC composites. A comprehensive experiment matrix including Kr irradiation, He pre-implantation with sequential Kr irradiation as well as simultaneous dual beam at 1073 K to 16 dpa and 2400 appm He (150 appm/dpa) was performed using 800 keV Kr and 50 keV He ions. With the support of MD results, the impact of relative concentration ratio of vacancies and helium atoms on the bubble evolution was systematically investigated and the corresponding mechanism was further unraveled, which provides the basis of limiting the bubble density in SiC/SiC composites. Additionally, the direct evidence for the competition of irradiation-assisted bubble growth and re-dissolution was in-situ observed in SiC matrix for the first time.

Mg2Al4Si5O18 as a novel bond coat material for advanced thermal/environmental barrier coatings on SiCf/SiC composites

This study proposes cordierite (Mg2Al4Si5O18, MAS) as a novel bond coat material for thermal/environmental barrier coatings (T/EBC), deposited using atmospheric plasma spray on SiC fiber reinforced SiC matrix composites (SiCf/SiC-CMCs) coupons, forming a Mg2Al4Si5O18/Yb2Si2O7/Yb2SiO5/LaMgAl11O19 coating system. The phase composition and thermal properties of the as-sprayed MAS coating were investigated, revealing cordierite as the primary phase in the as-sprayed coating with minor amounts of spinel and quartz phases which disappeared after heat treatment. Additionally, the as-sprayed MAS coating exhibited a low thermal expansion coefficient (3.19 × 10−6 K−1). The thermal cycling behavior and steam corrosion performance of the T/EBC coating system with cordierite as the bond coat were studied. Detailed analysis revealed that during thermal cycling tests, the coating failure was primarily related to liquid-phase sintering caused by eutectic reactions. In steam corrosion tests, the coating delamination was linked to the formation and growth of cracks and corrosion voids due to the residual stress release.

Influence of fiber surface properties of SiCf/SiC composites on the interfacial debonding behavior

SiC fiber-reinforced SiC matrix composites (SiCf/SiC) containing BN interphase were fabricated via CVI and MI. For fiber-treated SiCf/SiC composites, cracks that initiate in the matrix tend to deflect between the fiber and the BN interphase when it reaches the fiber/matrix region, and the interface debonding and sliding occurs between the BN interphase and the matrix when fibers are pulled out. The mechanical properties of fiber-treated SiCf/SiC composites are significantly improved. The roughness and chemical properties are analyzed for the treated and as-received SiC fibers. The relationship between the surface chemical composition and roughness of fibers and the fiber/interphase adhesion force is discussed. The composites prepared from the treated fibers are confirmed to have stronger fiber/interphase adhesion force, which is caused by the improvement of surface roughness, the decrease of SiO2 on the fiber surface, and the interinfiltration of BN and excess C on the treated fiber surface.

Characterization of BN interface and its effect on the mechanical behavior of SiCf/SiC composites

The boron nitride (BN) interface of SiC fiber-reinforced SiC matrix (SiCf/SiC) composites was fabricated by chemical vapor infiltration (CVI) using BCl3 and NH3 as precursor. The microstructure and chemical composition of the BN interface were characterized. The influence of the coating thickness on the tensile behavior of SiCf/SiC composites was then evaluated. The BN interface synthesized at 800 °C has a low degree of crystallization and displays a quasi-isotropic microstructure. The ratio of element B to element N is near 1 and the oxygen content is about 10%. Meanwhile, the electron structure of B, N atoms near the SiC fiber surface have more sp2 hybridization state. Increasing the BN interface thickness exerts a critical role in decreasing the interfacial sliding stress which improves the tensile strength and toughness of SiCf/SiC composites. The optimal thickness of the BN interface is about 670 nm and further increasing the thickness exhibits little improvement on the mechanical properties of SiCf/SiC composites.

Excellent ablation resistance and reusability of silicon carbide fiber reinforced silicon carbide composite in dissociated air plasmas

This work explores the potentials of SiC fiber reinforced SiC matrix composites (SiCf/SiC) with SiC coating to resist aerodynamic ablations for thermal protection purpose. A plasma wind tunnel is employed to evaluate their anti-ablation property in dissociated air plasmas. The results suggest a critical ablation temperature of SiC coated SiCf/SiC, ≈ 1910 °C, which is the highest ever reported in literatures. Benefited by ‘all-SiC’ microstructures and relative flat ablated surfaces, the SiCf/SiC is still ablation-resistant up to ≈ 1820 °C after the occurrence of ablation. This implies an excellent ablation resistance and reusability property of SiCf/SiC, which surpasses that of traditional carbon fiber reinforced composites. Finally, an ablation mechanism dominated by surface characteristic is proposed. For the SiC coated SiCf/SiC, ablation is prone to take place at surface cracks formed by thermal mismatch; while for the ablated SiCf/SiC, ablation is triggered at the exposed fiber bundles which is over-heated in the plasmas.

In-situ CT characterization of 2D woven SiCf/SiC composite loading under compression

Abstract SiC fiber-reinforced SiC matrix composites (SiCf/SiC) with 2D woven fabric as preform were tested under compression with in-situ X-ray computed tomography. The microstructure and damage evolution of the material under continuous loading levels were accurately revealed by image reconstruction of CT data. There were inhomogeneous pores in SiCf/SiC composite because of the un-uniform fiber distribution in the preform. The result also showed that 2D woven SiCf/SiC composite had obvious non-linear characteristics by its compressive load–displacement curve, and the damage modes included transverse matrix cracking, interlayer cracking, longitudinal matrix cracking, and fiber bundle fracture. Matrix cracking tended to occur near the pores or holes of the material, and the number of longitudinal cracks was relatively high compared to the number of transverse cracks.

Identifying Chemical Disordering in Irradiated SiC Fiber-Reinforced SiC Matrix Composites with High-Throughput Correlative Microscopy

Identifying Chemical Disordering in Irradiated SiC Fiber-Reinforced SiC Matrix Composites with High-Throughput Correlative Microscopy

Densification behavior of monolithic SiC fabricated by pressureless liquid phase sintering method

As a preliminary investigation of process development for SiC fiber-reinforced SiC matrix composites (SiCf/SiC composites) via a pressureless liquid phase sintering (PLPS) method, the manufacturing process parameters of monolithic SiC fabricated with/without very low pressure during the sintering under high temperature (1850 and 1900 °C) were optimized. Two kinds of sintering additive system (only Al2O3 and Al2O3–Y2O3 mixtures) can be achieved full densification corresponding to 99% of the theoretical density without high pressure during the sintering. Monolithic SiCs of both sintering additive systems applied with prepressure of 20 or 40 MPa possessed the flexural strength and porosity comparable to those of conventional liquid-phase sintered SiC with high pressure during the sintering. The low pressure (0.63 MPa) during sintering reduced the densification in particular for the materials sintered with just Al2O3. The additions of BN particles led to a gradual decrease in mechanical strength with an increase in porosity.

Texture control of pyrolytic carbon coatings and effects of coating thickness on the tensile properties of SiC fibers

High-textured pyrolytic carbon (PyC) is the ideal interface for SiC fiber-reinforced SiC matrix (SiCf/SiC) composites. To prepare high-textured PyC coatings on SiC fibers efficiently, chemical vapor deposition (CVD) technique was applied with the single precursor ethanol. The effects of CVD parameters on the morphology and textures of PyC were investigated in detail. Rough laminar (RL), smooth laminar (SL) and regenerative laminar (ReL) PyC could be obtained by controlling the CVD parameters. High-textured RL PyC could be stably synthesized in a large distance range in the horizontal tube furnace at 1150 °C and 10–20 kPa (total pressure), which inferred that low temperature and negative pressure were beneficial to the formation of RL PyC. Conversely, when the temperature was up to 1350 °C, the textures of PyC at different deposition positions varied considerably. In the vicinity of isothermal zone, the texture evolution of PyC with deposition positions followed the pattern of SL→RL→SL, which could be ascribed to the ratio change of the small linear hydrocarbons (fillers) and the aromatic hydrocarbons (particles) in the gas phase. The texture evolution followed the Particle-Filler model. In addition to PyC textures, the PyC coating thickness played a critical role in regulating the mechanical properties of SiC fibers and SiCf/SiC composites. In the present work, the effects of thickness of RL PyC coatings on the tensile properties of SiC fibers were investigated. The SiC fibers with 0.3 μm RL PyC coating showed the highest average tensile strength (2735 MPa) and Weilbull modulus (10.34), which might be ascribed to the repair of fiber surface defects and the appropriate stress state between fibers and coatings. The results could provide essential data for the interface design and optimization of SiCf/SiC composites.

Microstructure and properties of pressure-less joining of SiCf/SiC composites by Ti–Si alloys

Prepared with pure Ti and Si powders as raw materials, the Ti16Si84 alloy (at. %) was obtained through refining in an intermediate frequency magnetic induction furnace. In this study, a novel method to join SiC fiber-reinforced SiC matrix composites (SiCf/SiC composites) under non-pressurized conditions is proposed using Ti16Si84 alloy foil as the joining material. The joining process was optimized, and the wettability, microscopic morphology, and bonding reaction of the joint were studied, along with the fracture characteristics and the bonding mechanism. Additionally, the corrosion resistance of the joints was examined in pure static water with high-dissolved oxygen (246 ppm) at 360 °C and 18.6 MPa. The results showed that Ti16Si84 alloy has good wettability with SiCf/SiC, enabling it to join SiCf/SiC successfully. The joint was composed of SiC, TiSi2, and Si, and there was no intermediate between them. When the brazing temperature was 1410 °C, the shear strength of the joint reached 42.5 MPa, and the joint integrity was favorable. After the shear test, numerous SiCf/SiC composites were torn by the solder, indicating their advantageous shear properties and high joint strength. After three days of corrosion, the joint samples' weight showed almost no changes. The corrosion depth was less than 20 μm and the residual shear strength of the corroded joined samples was 38.37 MPa, indicating excellent hydrothermal corrosion resistance of the joint material.

Oxidation behaviors of carbon fiber reinforced multilayer SiC-Si3N4 matrix composites

Oxidation behaviors of carbon fiber reinforced SiC matrix composites (C/SiC) are one of the most noteworthy properties. For C/SiC, the oxidation behavior was controlled by matrix microcracks caused by the mismatch of coefficients of thermal expansion (CTEs) and elastic modulus between carbon fiber and SiC matrix. In order to improve the oxidation resistance, multilayer SiC-Si3N4 matrices were fabricated by chemical vapor infiltration (CVI) to alleviate the above two kinds of mismatch and change the local stress distribution. For the oxidation of C/SiC with multilayer matrices, matrix microcracks would be deflected at the transition layer between different layers of multilayer SiC-Si3N4 matrix to lengthen the oxygen diffusion channels, thereby improving the oxidation resistance of C/SiC, especially at 800 and 1000 °C. The strength retention ratio was increased from 61.9% (C/SiC-SiC/SiC) to 75.7% (C/SiC-Si3N4/SiC/SiC) and 67.8% (C/SiC-SiC/Si3N4/SiC) after oxidation at 800 °C for 10 h.

In-situ formation of Ti3SiC2 interphase in SiCf/SiC composites by molten salt synthesis

Titanium silicon carbide (Ti3SiC2) film was synthesized by molten salt synthesis route of titanium and silicon powder based on polymer-derived SiC fibre substrate. The pre-deposited pyrolytic carbon (PyC) coating on the fibre was utilized as the template and a reactant for Ti3SiC2 film. The morphology, microstructure and composition of the film product were characterized. Two Ti3SiC2 layers form the whole film, where the Ti3SiC2 grains have different features. The synthesis mechanism has been discussed from the thickness of PyC and the batching ratio of mixed powder respectively. Finally, the obtained Ti3SiC2 film was utilized as interphase to prepare the SiC fibre reinforced SiC matrix composites (SiCf/Ti3SiC2/SiC composites). The flexural strength (σF) and fracture toughness (KIC) of the SiCf/Ti3SiC2/SiC composite is 460 ± 20 MPa and 16.8 ± 2.4 MPa∙m1/2 respectively.

Material combination conditions of the polymer infiltration and pyrolysis-melt infiltration hybrid process to make a dense and uniform matrix of SiC fiber-reinforced SiC matrix composite

Material combination conditions of the polymer infiltration and pyrolysis-melt infiltration hybrid process to make a dense and uniform matrix of SiC fiber-reinforced SiC matrix composite

Experimental study on flash radiation and damage characteristics of C/SiC composites induced by hypervelocity impact

Continuous carbon fiber-reinforced SiC-matrix composites(C/SiCs) have been developed for key thermal structures of aerospace and hypersonic vehicles, which is important to research on thermal and dynamic behavior of C/SiC composites under hypervelocity impact for understanding the response characteristics of C/SiC composites subjected to shock loading. The projectiles made of C/SiC composites and silicon carbide(SiC) were loaded by two-stage light gas gun to impact C/SiC plates with impact velocities from 1.35 km/s to 3.5 km/s and impact angle of 90°, the damage morphology of C/SiC plates, the evolutionary process of thermal radiation and impact pressure were obtained. The experimental results show that fiber failure of C/SiC composites consumes part of the initial kinetic energy during hypervelocity impact, therefore, the carbon fiber improves the fracture toughness of SiC matrix. Under the experimental conditions given in this paper, the lower impact velocity is, the greater differences of thermal and dynamic response between the two kinds of projectiles are. Compared with SiC projectiles, the C/SiC composite projectiles have longer flash radiant duration and lower flash radiant temperature. However, when the impact velocity is higher, the flash radiant duration and the flash radiant temperature of the two kinds of projectiles are similar due to the fiber fracture of the C/SiC composite, and the peak of flash radiant temperature appears before flash radiant intensity during impact process. For the damage characteristics of C/SiC plates, the higher impact velocity is, the smaller perforation diameter of C/SiC plates is, and the shape is more regular. With the decrease of the impact velocity, the damage morphology of C/SiC plates is irregular, and the matrix powdering is more serious.

Monitoring Damage in Nonoxide Composites at High Temperatures Using Carbon-Containing CVD SiC Monofilament Fibers as Embedded Electrical Resistance Sensors

Abstract Electrical resistance (ER) has become a technique of interest for monitoring SiC-based ceramic composites. The typical constituents of SiC fiber-reinforced SiC matrix composites, SiC, Si, and/or C, are semiconducive to some degree resulting in the fact that when damage occurs in the form of matrix cracking or fiber breakage, the resistance increases. For aero engine applications, SiC fiber reinforced SiC, sometimes Si-containing, matrix with a boron nitride (BN) interphase are often the main constituents. The resistivity of Si and SiC is highly temperature dependent. For high temperature tests, electrical lead attachment must be in a cold region which results in strong temperature effects on baseline measurements of resistance. This can be instructive as to test conditions; however, there is interest in focusing the resistance measurement in the hot section where damage monitoring is desired. The resistivity of C has a milder temperature dependence than that of Si or SiC. In addition, if the C is penetrated by damage, it would result in rapid oxidation of the C, presumably resulting in a change in resistance. One approach considered here is to insert carbon “rods” in the form of CVD SiC monofilaments with a C core to try and better sense change in resistance as it pertains to matrix crack growth in an elevated temperature test condition. The monofilaments were strategically placed in two nonoxide composite systems to understand the sensitivity of ER in damage detection at room temperature as well as elevated temperatures. Two material systems were considered for this study. The first composite system consisted of a Hi-Nicalon woven fibers, a BN interphase and a matrix processed via polymer infiltration and pyrolysis (PIP) which had SCS-6 monofilaments providing the C core. The second composite system was a melt-infiltrated (MI) prepreg laminate which contained Hi-Nicalon Type S fibers with BN interphases with SCS-ultramonofilaments providing the C core. The two composite matrix systems represent two extremes in resistance, the PIP matrix being orders of magnitude higher in resistance than the Si-containing prepreg MI matrix. Single notch tension–tension fatigue tests were performed at 815 °C to stimulate crack growth. Acoustic emission (AE) was used along with ER to monitor the damage initiation and progression during the test. Post-test microscopy was performed on the fracture specimen to understand the oxidation kinetics and carbon recession length in the monofilaments.

Effect of pyrolytic carbon interphase on mechanical properties of mini T800-C/SiC composites

The effect of pyrolytic carbon (PyC) thickness on the tensile property of mini T800 carbon fiber reinforced SiC matrix composites (C/SiC) was studied. PyC interphase was prepared by chemical vapor infiltration (CVI) process using C3H6–Ar as gas source, the PyC thickness was adjusted from 0 to 400 nm, and then the SiC matrix was prepared by CVI process using methyltrichlorosilane (MTS)–H2–Ar as precursor and gas source. The results showed that the tensile strength of mini T800-C/SiC increased first and then decreased with the increase of the PyC thickness. When the thickness of PyC was 100 nm, the average strength reached the maximum value of 393 ± 70 MPa. The Weibull modulus increased from 2.0 to 8.06 with the increase of PyC thickness, and the larger the Weibull modulus, the smaller the dispersion, which indicated that the regulation of PyC thickness was conducive to improve tensile properties.

A multiscale modeling for predicting the thermal expansion behaviors of 3D C/SiC composites considering porosity and fiber volume fraction

Coefficients of thermal expansion (CTEs) are an essential design criterion of the three-dimensional carbon fiber reinforced SiC matrix composites (3D C/SiC). Representative volume element (RVE) models of microscale, void/matrix, and mesoscale developed in this work were used to investigate the CTEs of these composites. A coupled temp-displacement steady-state analysis step was created for assessing the thermal expansions behaviors of the composites by applying periodic displacement and temperature boundary conditions. Three RVE models of cuboid, hexagonal and fiber random distribution were respectively established to comparatively study the influence of fiber package pattern on the CTEs at microscale. Similarly, the effects of different void size, locations, and shapes on the CTEs of the matrix are comparatively analyzed by the void/matrix models. The prediction results at mesoscale corresponded closely to the experimental results. The effect of the porosities on the CTEs was studied by the void/matrix RVE models. The voids were effective in lowering the CTE of the 3D C/SiC composites. Furthermore, the effect of fiber volume fractions on the CTE were also taken into consideration. Equal in-plane and out-of-plane CTEs were realized by selecting appropriate fiber volume fractions for the different directions. The multiscale models developed in this work can be used to predict the thermal expansion behaviors of other complex structure composites.

Influence of porosity on anisotropic thermal conductivity of SiC fiber reinforced SiC matrix composite: A microscopic modeling study

The effect of porosity on the effective thermal conductivities calculation for continuous SiC fiber reinforced SiC matrix composites (SiCf/SiC) was studied in this work by finite element modeling. A three-dimensional representative volume element (RVE) containing detailed geometric features (fibers, matrix, fiber coatings and pores) was generated to rebuild the microstructure of SiCf/SiC and used to numerically calculate the effective transversal and longitudinal thermal conductivities of SiCf/SiC. Markworth model and parallel model were chosen as theoretical models to calculate the transversal and longitudinal thermal conductivities respectively. The numerical results obtained by RVE models were validated by comparison with the theoretical and experimental results. The results highlight the existing theoretical models cannot well predict the transversal thermal conductivity of SiCf/SiC with the existence of pores. In the analysis of the effect of porosity, real pore structure in SiCf/SiC was investigated to revel the relationship between porosity and the effective thermal conductivities. In the case of longitudinal thermal conductivity, the parallel model plus the linear term of porosity can still be used to predict the longitudinal thermal conductivity. As for the transversal thermal conductivity, a more proper Markworth model for SiCf/SiC transversal thermal conductivity calculation calibrated by incorporating porosity is proposed to efficiently calculate the transversal thermal conductivity at the end of this paper.

Preparation and tensile behavior of SiCf/SiC mini composites containing different types and thicknesses of interphase

SiC fiber-reinforced SiC matrix (SiCf/SiC) composites are promising materials for high-temperature structural applications. In this study, KD-II SiC fiber bundles with a C/Si ratio of approximately 1.25 and an oxygen amount of 2.53%, were used as reinforcement. PyC interphase, PyC-SiC co-deposition interphase I and II, with different thicknesses, and SiC matrix were deposited into the SiC fiber bundles by using chemical vapor infiltration (CVI) to form SiCf/SiC mini composites. When the thickness of the interphase is approximately 1000 nm, the ultimate tensile stress and strain of SiCf/SiC mini composites with PyC-SiC co-deposition interphase I can reach 1120.0 MPa and 0.72%, respectively, which are significantly higher than those of SiCf/SiC mini composites with a PyC interphase (740.0 MPa, 0.87%) and PyC-SiC co-deposition interphase II (645.0 MPa, 0.54%). The effect of thicknesses and types of interphase on tensile fracture behavior of mini composites and then the fracture mechanism are discussed in detail.

Evolution of microstructure and nanohardness of SiC fiber-reinforced SiC matrix composites under Au ion irradiation

Evolution of microstructure and nanohardness of a new type of SiCf/SiC composite under a 6 MeV Au ion irradiation up to 90 displacements per atom at 400 °C was studied. Scanning transmission electron microscopy reveals that the irradiation has induced enrichment of carbon at the grain boundaries in the fibers. This is attributed to the accumulation of C interstitials generated by the irradiation. The disappearance of {200} diffraction ring of 3C–SiC indicates that a phase transition from 3C–SiC to Si has occurred during irradiation. In addition, the hardness of SiC fiber increased after irradiation, which is due to the pinning effect caused by irradiation-induced defects. The pyrolytic-carbon interphase that contains Si-rich nano-grains in the composite has the highest irradiation tolerance as it maintained its basic morphology and graphitic nature after a radiation damage dose up to 90 dpa. Twins are the main internal defects in the SiC matrix of the SiCf/SiC composite, which grew up and resulted in the decrease of the number of twinning boundaries under irradiation. No significant microstructure change has been observed in the SiC matrix except a limited number of dislocation loops at the peak irradiation damage region. The entire matrix still maintained its hardness after irradiation.