Continuous SiC Fiber Research Articles

Hoop tensile properties and crack propagation investigation of 2D braided SiCf/SiC composite tubes: Experiments and simulations

SiCf/SiC composites are promising candidates for advanced pressurized water reactors (PWRs) fuel cladding materials due to their enhanced accident tolerance. Their mechanical properties are strongly influenced by the braided structure of continuous SiC fibers. This study fabricated SiCf/SiC composite tubes with braid angles ranging from 30° to 50°, evaluating their hoop tensile properties through expansion-due-to-compression (EDC) experiments and analyzing the damage process using finite element method simulation. Results indicate that variations in braid angles significantly affect structural density, thereby impacting mechanical strength under hoop tensile stress. Increased braid angles result in smaller pore units and higher pore density, leading to local stress concentrations and varied deflections at overlapping regions. The dynamic propagation behavior of cracks was investigated through acoustic and structural nondestructive testing methods. Finite element analysis of different braid configurations highlights the pivotal role of pore units in the initiation and propagation of hoop tensile cracks. This study enhances the understanding of toughening structures in 2D braided composites and provides a theoretical basis for future accident-tolerant fuel cladding design.

Solidification behavior of SiCf/Ti17 induced by fixed-point laser surface remelting

Taking advantage of laser additive manufacturing, continuous SiC fiber reinforced titanium matrix composites (SiCf/TMCs) with low density and excellent mechanical properties can be used to hybrid-fabricate large components with complex shape for aerospace applications. However, due to the anisotropy in both microstructure and heat transfer ability, the high-density and rapid heat input from laser during hybrid manufacturing process will cause the non-uniform damage of fibers and various solidification microstructure in the molten pool. In order to understand the solidification behavior of molten pool in SiCf/Ti17 composites, the fixed-point laser surface remelting was used to bring in rapid and symmetrical heat input. With the decrease of temperature from center to edge of the molten pool, both fiber damage degree and the contents of Si and C elements in melt decreased. The solidification microstructure contains TiCx, Ti5Si3 and β-Ti, and their morphology varies according to the melt composition. SiC fibers act as heterogeneous nucleation sites for first solidified phases and promote their preference growth along the radial direction of fibers resulting from the excellent heat transfer ability. The faceted Ti5Si3 grains solidified through peritectic reaction L+TiCx→Ti5Si3 exhibit strong <0001> texture.

Effect and mechanism analysis of free carbon on the oxidation behaviour of SiC fibres

Continuous SiC fibres have received widespread attention in the field of aero-engines due to their excellent mechanical properties and oxidation resistance. Free carbon is one of the main factors affecting the oxidation behaviour of SiC fibres, but its role and influence are still unclear. The oxidation behaviour of two types of SiC fibres with similar oxygen contents and crystallite sizes but different carbon-silicon ratios was investigated in this study. Free carbon did not significantly influence strength retention, but positively affected elastic modulus retention. The oxidised carbon-rich SiC fibres exhibited a thinner, smoother, and denser oxide scale. The oxidation rate of the carbon-rich fibres was lower than that of near-stoichiometric fibres after oxidising at 1200 °C. The oxidation activation energies of both were 170.44 ± 15.80 and 234.45 ± 24.94 kJ/mol, respectively. Free carbon can inhibit oxidation scale crystals at the beginning of oxidation while promoting crystallisation scale as oxidation intensifies. The oxidation scale crystals of carbon-rich fibres are mainly controlled by the interface, whereas those of near-stoichiometric fibres are mainly controlled by diffusion. A stress expansion zone was formed at the interface of the oxidised SiC fibres. Free carbon can enhance the internal stress of the stress expansion zone, resulting in lower residual compressive stress on the surface of carbon-rich SiC fibres. These results are significant for improving the oxidation resistance of SiC fibres by retaining free carbon.

High performance SiC/SiOC composites with in situ carbon interface

A novel SiC/SiOC composite was prepared via the polymer infiltration and pyrolysis (PIP) process by using a low-cost poly-methyl-silsesquioxane resin as matrix precursor and continuous thin SiC fibers as reinforcements. A carbon coating is in situ formed on SiC fiber prior to the composite processing. The high yield of the resin resulted in a short period of the composites achieving densification. The composites exhibited pseudoplastic fracture with a high flexural strength of 315.10 MPa and a fracture toughness of 21.6 MPa m1/2. With the help of the in situ coating, the SiC fibers pulled out of the matrix independently, leading to optimization of the reinforcing effect and enhancement of the composite strength compared to chemical vapor deposition (CVD) fiber coatings. After annealing in N2 at 1000 °C for 10 h, the strength retention rate of the composites is 92.21%, showing excellent stability to be used in thermal structural components.

Synthesis of Polytitanocarbosilane and Preparation of Si–C–Ti–B Fibers

Continuous SiC fiber is a kind of high–performance ceramic fiber that combines many advantages, such as high strength, high modulus, high hardness and low density. It has excellent mechanical properties, high–temperature and oxidation resistance, which could be applied as essential reinforcement in advanced ceramic matrix composites (CMCs) in the fields of aerospace and advanced weaponry. Melt–spinnable polytitanocarbosilane (PTCS) is an important precursor, which can be used to prepare continuous SiC fibers through a precursor–derived method. In this work, low–softening–point polycarbosilane (LPCS) and tetrabutyl titanate were used to prepare polytitanocarbosilane with a ceramic yield of 67.5 wt% at 1000 °C. FT–IR, TGA, GPC, 1H NMR, 29Si NMR, and elemental analysis were used to analyze the composition and structure of the PTCS precursor. Finally, Si–C–Ti–B fibers with an average tensile strength of 1.93 GPa were successfully prepared by melt spinning, pre–oxidation, pyrolysis, and high–temperature sintering of the PTCS precursor. The strength retention rates were 71.5% and 79.8% after heat treatment at 1900 °C and 2000 °C under an argon atmosphere for 1 h, respectively. The strength retention rates of Si–C–Ti–B fibers are higher than those of commercial Hi–Nicalon fibers, Tyranno ZMI fibers and Hi–Nicalon S fibers. This work can lay a theoretical foundation and technical support for developing high-performance SiC ceramic fibers containing titanium and their ceramic matrix composites.

Preparation of SiCf/Si–O–C composites by impregnation pyrolysis of polysiloxane and its electromagnetic wave absorption properties

AbstractHigh‐temperature structural electromagnetic wave (EMW) absorption materials are increasing in demand because they can simultaneously possess the functions of mechanical load‐bearing, heatproof, and EMW absorption. Herein, SiCf/Si–O–C composites were prepared by precursor impregnation pyrolysis using continuous SiC fibers needled felt as reinforcement and polysiloxane as a precursor, respectively. The phase composition, microstructure, complex permittivity, and EMW absorption properties of SiCf/Si–O–C composites after annealing at various temperatures were investigated. The annealing at 1400–1500°C affects positively the EMW absorption performance of the composites, because the β‐SiC microcrystals and SiC nanowires were generated by the activation of carbothermal reduction reaction in the composites, and the aspect ratio of SiC nanowires increased with the rise of temperature. The composites exhibit optimal EMW absorption performance, with the effective absorption bandwidth covering the entire X‐band and the minimum reflection loss (RLmin) of −32.8 dB at 4.0 mm when the annealing temperature is raised to 1500°C. This is because that the impedance matching is improved as the rising of ε′ and decreasing of ε″ due to the conversion of free carbon in the composite into SiC nanowires.

Effect of Sintering Temperature on Properties of SiC Fiber Reinforced Tungsten Matrix Composites

Continuous SiC fibers were used to toughen tungsten in this work. The composites were prepared by hot-press using W powders sintered from 1500°C to 1900°C for 1 h with 20 MPa pressure. Phases changes, microstructure, mechanical and thermal properties of composites were examined. Besides, the kinetics between SiC and W was also studied. The stress-strain curve had pseudo-ductility at room temperature, except for 1900°C sintered samples due to complete damage of fiber. Thermal conductivity was calculated from two directions: in-plane and through-plane directions (parallel and vertical to fiber direction), in which through-plane direction display higher thermal conductivity than other direction. Besides, severe reaction was verified between SiC and W, and the reaction rate increased 18 times when temperature increased from 1500°C to 1700°C. Therefore, it is suitable to use SiC fiber to reinforce W to ameliorate the brittleness with limited reaction between fiber and matrix.

The high-temperature degradation mechanism of W-core SiC fibers

Continuous W-core SiC fiber has been regarded as a promising reinforcement, exhibiting huge potential for applying to hypersonic aircraft commonly suffering from harsh environment with high-temperature short-term characteristic. In this work, the micro/nano-scale investigation on heat treatment (HT) induced dynamic evolution of microstructure in W-core SiC fiber was performed to reveal strength degradation mechanism. It is revealed that the integrity of surface C coating can be well retained even after 1400 ℃/2 h HT avoiding the appearance of surface-dominated fracture mode. In the SiC sheath, only defects annihilation and crystallization transiting the disorder structure into well-crystallized β-SiC columnar grains instead of excessive growth happens, and thus HT induced sharp strength degradation cannot be governed by the microstructural variation of SiC sheath. After high-temperature HT, the interfacial reaction layer continuously thickens with increasing HT temperature that is proportional to fracture mirror zone radius, responsible for strength degradation induced by high-temperature short-term HT.

Properties of super heat-resistant silicon carbide fibres with in situ BN coating

An in situ BN coating was prepared on the surface of a nearly stoichiometric continuous SiC fibre with trademark Cansas-3301 (C3). The coated fibre was then subjected to continuous pyrolysis at 1800 °C, obtaining a fibre named Cansas-BN-1800 (C18). After annealing in Ar at 1500 °C for 1 h, the strength retention ratio of C3 was 49%, and that of C18 was almost unchanged. The strength decrease of the C3 fibre was mainly caused by the formation of surface defects resulting from fibre decomposition and active oxidation. However, the in situ BN coating on C18 protected the fibre from forming surface defects, resulting in high strength. Due to slight growth of the grain and purification of the grain boundary during fast heating at 1800 °C, C18 showed excellent creep resistance in the range of 1200–1500 °C.

Effect of tungsten matrix on the mechanical property of SiC fiber reinforced tungsten composites with foils fabricated at 1700 °C

• Continuous SiC fiber reinforced tungsten composites with foils were fabricated at 1700 °C. • Composite with foils display pseudo ductility at room temperature, especially in the case of thicker foil. • Foils recrystallized after sintering. The SiC fiber reinforced tungsten (W) composites were prepared by hot press process at 1700 °C for 1 h under a pressure of 20 MPa with W foils as matrix. The effect of thickness of W foils on the phases, microstructure, and mechanical properties of the composites were investigated in this work. In addition, the recrystallization temperature of W foil used in this work was confirmed. The results demonstrated that the composites with 0.08 mm foil exhibited better mechanical property with 197 MPa and high pseudo ductility than those of the 0.05 mm foil composites of 129 MPa. In addition, the used foils after sintering have recrystallized, and W can be identified by XRD. Therefore, SiC fiber can be an effective reinforcement to toughen W and dense foils as matrix can prevent the reaction partially.

Influence of Al particles as infiltration promoters on the interfacial reaction and mechanical property of a continuous SiC fiber/AZ91 composite fabricated by a low-pressure infiltration method

In this study, Mg alloy-based composites (MMC: metal matrix composite) with uniaxially oriented continuous SiC fibers were fabricated using a low-pressure infiltration method. Next, the influence of Al particles as the infiltration promoter on the interfacial reaction between the SiC fibers and the Mg alloy matrix was investigated by means of scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. In the presence of Al particles, β-Mg17Al12 was preferentially precipitated around the SiC fibers. The SiC fibers and the Mg alloy matrix did not react directly and remained bonded at the fracture surface. In contrast, in the absence of Al particles, whisker-like Al4C3 was observed around the SiC fiber, and a reaction phase consisting of MgO and Mg2Si was observed in the circumferential part inside the SiC fiber. The detachment occurred between the SiC fibers and the Mg alloy matrix at the fracture surface.

Investigation of interface debonding behaviour in a unidirectional SiC fibre reinforced Ti-17 composite by a single fibre push-out technique

The debonding behaviour at the fibre/matrix interface in a unidirectional continuous carbon-coated SiC fibre reinforced Ti-17 composite was investigated. Single fibre push-out testing on thin slice specimen by micro-indentation was employed to evaluate the interface debonding strength. In order to investigate interface debonding modes, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilised to observe the microstructure at the fibre/matrix interface region after the fibres were pushed out. It is found that the interface debonding strength is evaluated to be 108.2 MPa in the composite. The interface debonding occurs at the interface between the interface reaction zone (RZ) and the carbon coating on the fibre surface. The carbon coating/SiC fibre interface and the RZ/matrix interface remain intact after the fibre was pushed out.

Effect of C/SiC interphase on interfacial and mechanical properties of SiC fiber reinforced mullite matrix composites

Continuous SiC fiber reinforced mullite (SiCf/Mu) matrix composite was fabricated via sol–gel process. The capability of fiber coatings to weaken the interfacial interaction, thus to enhance the fracture toughness of the SiCf/Mu composite was explored. The results show that the SiC interphase fabricated by chemical vapor deposition (CVD) process was columnar-grain structured. A thin carbon layer was also produced during the CVD process, forming C/SiC interphase. The interfacial shear strength of the SiCf/Mu composite was significantly reduced from ≈537 to ≈115 MPa after the introduction of C/SiC interphase, as quantified by in situ fiber push-in tests. Accordingly, the macro fracture toughness of the composite was remarkably enhanced from ≈0.9 to ≈10.5 MPa m1/2. The work highlights the efficiency of using C/SiC interphase to weaken the interfacial bonding, thus greatly toughen the SiCf/Mu composite.

Improved thermal stability of SiCf/SiC ceramic matrix composites fabricated by PIP process

Improvement of the thermal stability of continuous SiC fiber reinforced SiC ceramic matrix composites (SiCf/SiC CMC) by the pre-treatment of SiC fillers and the suppression of oxidation during polymer impregnation and pyrolysis (PIP) process were investigated. Dense SiCf/SiC CMCs were fabricated using the slurry infiltration and PIP process under a purified argon atmosphere. Structure and mechanical properties of the SiCf/SiC CMC heated at different temperatures were evaluated. The flexural strength of the SiCf/SiC CMC decreased only 15.3%after heating at 1400 ?C, which exhibited a clear improvement compared with the literature data (49.5% loss), where severe thermal deterioration of SiCf/SiC composite occurred at high temperatures by the crystallization and decomposition of the precursor-derived ceramic matrix. The thermal stability of the SiCf/SiC CMC fabricated by PIP process was improved by the pre-treatment of SiC fillers for removing oxides and the strict atmosphere control to prevent oxidation.

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 of SiC ceramic fiber from a photosensitive polycarbosilane

Curing treatment is essential for ceramic precursors to maintain their shape during pyrolysis. In this study, a photosensitive SiC ceramic precursor was synthesized by chlorinating partial Si–H groups of polycarbosilane (PCS) with Cl2 followed by reacting with hydroxyethyl acrylate. According to 1H NMR and element analysis, about 10% structural unit of PCS was grafted with the acrylate group. After mixing with photo-initiator, the acrylate-grafted PCS transformed from soluble and fusible state to insoluble and non-fusible state under UV light. Its curing rate with related ceramic yield and oxygen content were compared with PCSs cured by the traditional air oxidation and electronic radiation. By electrospinning synchronized with UV illumination and pyrolyzing the acrylate-grafted PCS, one-dimensional continuous SiC fibers were prepared. The effects of pyrolysis temperature on the morphology, crystallographic structure and elemental composition were also characterized and discussed.

Residual stress variation in SiCf/SiC composite during heat treatment and its effects on mechanical behavior

Residual stress originated from thermal expansion mismatch determines the mechanical properties of ceramic matrix composites (CMCs). Here, continuous SiC fiber reinforced SiC matrix (SiCf/SiC) composites were fabricated by nano-infiltration and transient eutectic-phase (NITE) method, and the residual stress of the composites was investigated using high-temperature Raman spectrometer. With temperature increasing from room temperature to 1400 °C, the residual stresses of the matrix and the fiber decrease from 1.29 to 0.62 GPa and from 0.84 to 0.55 GPa in compression respectively, while that of the interphase decreases from 0.16 to 0.10 GPa in tension. The variation of residual stress shows little effect on the tensile strength of the composites, while causes a slight decrease in the tensile strain. The suppression of fiber/matrix debonding and fiber pulling-out caused by the residual stress reduction in the interphase is responsible for the decreasing tensile strain. This work can open up new alternatives for residual stress analysis in CMCs.

Effect of Thermal Exposure on the Interface Microstructure and Interfacial Shear Strength of the SiC Fiber Reinforced AlFe5Si2 Matrix Composite

The effect of high temperature on the interface microstructure and interfacial shear strength of the continuous SiC fiber reinforced AlFe5Si2 matrix (45 vol.% SiCf/AlFe5Si2) composite was investigated. The composite was prepared by hot isostatic pressing (HIP), and then thermally exposed at 260/300/350/400/450 °C for 20/50/100 h, respectively. The interfacial shear strength of the composite with and without thermal exposure was measured by push-out test. The interface microstructure and phase compositions of the composite with and without thermal exposure were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Results showed that the interfacial reaction took place at the interface between SiC fiber and aluminum matrix and formed Al4C3 phase during the preparation process. The activation energy of Al4C3 growth at the C/Al interface was about 163 kJ/mol. With increasing the thermal exposure temperature and time, the interfacial shear strength of the composite declined, especially at temperatures above 400 °C. The brittle Al3.21SiO0.47 compound formed at temperatures above 400 °C mainly resulted in the severe strength deterioration of the interfacial reaction zone.

A study of reaction processes in SiC fiber reinforced Ni-Fe matrix composite during HIP

ABSTRACT Binary Ni-Fe metal matrix composite containing continuous W-core SiC fibers was fabricated by hot isostatic pressing (HIP) method to study the interface reaction processes. Interfacial reaction products were analyzed via field emission scanning electron microscope, electron probe microanalysis and micro-zone X-ray diffractometer. The results indicate that the reactions are so dramatical that even W core can decompose during the HIP process. The whole reaction processes of W-core SiC fiber can be divided into four stages. In stage 1, SiC starts to react with metal matrix to form Ni silicides with dissolved Fe element, graphite and Kirkendall void zone. In stage 2, SiC decomposes further and W core is exposed, then W core participates in reactions. In stage 3, SiC reacts completely, W core further reacts. In stage 4, W core decomposes completely and transform to be steady WC particles, which means the whole processes terminate. A model to clarify the mechanism of the reaction processes is proposed.

Interfacial reactions and matrix microstructure evolution in SiCf/Ti composites dominated by primary structure of Ti matrix

Abstract High-performance continuous SiC fiber reinforced titanium matrix composites (SiCf/Ti) are strongly required by aerospace vehicles, and their properties strongly depend on the microstructure of the interfacial reaction layer and the matrix. Thus, it is important to explore new routes to regulate these two SiCf/Ti components. In this work, α-phase-dominated and β-phase-dominated primary PVD Ti17 coatings were fabricated by controlling the bias voltage during physical vapor deposition (PVD). Their effects on the matrix microstructure evolution and interfacial reactions in SiCf/Ti after consolidation were further explored. It was found that compared with a primary α-Ti PVD Ti17 coating, a primary β-Ti PVD coating induced competitive growth between α-Ti and β-Ti grains in SiCf/Ti17 during consolidation. This yielded a smaller grain size and more β phase in the SiCf/Ti17 evolved from the primary β-Ti coating. In addition, a thicker reaction layer formed, as well as a lower interface strength and tensile strength in the SiCf/Ti17 evolved from a primary β-Ti coating, compared with the SiCf/Ti17 evolved from a primary α-Ti PVD Ti17 coating.