Use of Electrophoretic Impregnation and Vacuum Bagging to Impregnate SiC Powder into SiC Fiber Preforms

Techniques based on vacuum bagging (VB) and electrophoretic impregnation (EPI) have been investigated for the impregnation of SiC powder into layered Nicalon SiC fabric preforms. The aim was to produce preimpregnated samples for subsequent chemical vapor infiltration (CVI) with reduced intertow porosity that arises from the construction of the fabric layers while leaving unblocked the intratow porosity that is so indispensable for a successful infiltration. Because the goal was simply to learn about the ability to impregnate the samples, no interphase coating was applied to the fibers as would normally be used when producing SiC_f/SiC composites. While the VB process generally yielded much stronger preforms, depending on the pressure used and the powder particle size, it resulted in powder becoming located in the intratow rather than the intertow porosity. In contrast, provided an appropriate electrode arrangement was used, EPI offered the potential for a more controlled impregnation process with the powder primarily found in the intertow porosity; however, the preforms were very weak and delaminated easily. The combination of the two processes resulted in a very successful approach, with greater uniformity of particle infiltration and higher green strengths, while largely avoiding impregnating the intratow porosity.     

Effects of zirconium addition on microstructure and ablation resistance of carbon fibre reinforced carbon and SiC ceramic matrix composite prepared by reactive melt infiltration

Abstract

Carbon fibre reinforced C and SiC binary ceramic matrix composites (C/C–SiC) were fabricated by a quick and low cost reactive melt infiltration (RMI) method with Si–Zr25 and Si melts. Effects of zirconium addition in infiltrated Si melt on microstructure and ablation resistance of the composite were investigated. The composite by Si–Zr25 melt infiltration was composed of SiC, ZrC, C and a little amount of ZrSi₂ without residual silicon, overcoming the problem of residual silicon in C/C–SiC composite by Si RMI. Compared with the composite by Si melt infiltration, the ablation resistance of the composite by Si–Zr25 was greatly improved by zirconium addition due to ZrO₂ and SiO₂ protecting layer formed during ablation.     

Fabrication and characterization of carbon fiber reinforced SiC ceramic matrix composites based on 3D printing technology

A novel method has been developed to fabricate carbon fiber reinforced SiC (C_f/SiC) composites by combining 3D printing and liquid silicon infiltration process. Green parts are firstly fabricated through 3D printing from a starting phenolic resin coated carbon fiber composite powder; then the green parts are subjected to vacuum resin infiltration and pyrolysis successively to generate carbon fiber/carbon (C_f/C) preforms; finally, the C_f/C preforms are infiltrated with liquid silicon to obtain C_f/SiC composites. The 3D printing processing parameters show significant effects on the physical properties of the green parts and also the resultant C_f/C preforms, consequently greatly affecting the microstructures and mechanical performances of the final C_f/SiC composites. The overall linear shrinkage of the C_f/SiC composites is less than 3%, and the maximum density, flexural strength and fracture toughness are 2.83?±?0.03?g/cm³, 249?±?17.0?MPa and 3.48?±?0.24?MPa m^1/2, respectively. It demonstrates the capability of making near net-shape C_f/SiC composite parts with complex structures.     

Effect of fabric structure on the permeability and regeneration ability of porous SiCf/SiC composite prepared by CVI

In this paper, porous SiC_f/SiC composites are prepared by chemical vapor infiltration of SiC matrix on stitched fibrous preforms with different fabrics laminate structure. The microstructure of the fibrous preforms before and after infiltration of SiC matrix and the permeability and the regeneration efficiency of the porous SiC_f/SiC composites with different laminate structure have been determined. Experimental results show that the porous SiC_f/SiC composites with twill fabrics laminate structure exhibits a higher permeability with a higher volume porosity and mean pore diameter. In comparing the regeneration ability of two types laminate structure filter medium, as expected, the twill fabrics laminate structure exhibits a better regeneration efficiency than the plain fabrics laminate structure due to its higher air permeability.     

Characteristics of SiCf/SiC hybrid composites fabricated by hot pressing and spark plasma sintering

Abstract

Abstract

SiC fibre reinforced SiC–matrix ceramic composites were fabricated by electrophoretic deposition (EPD) combined with ultrasonication. Fine β-SiC powder and Tyranno-SA fabrics were used as the matrix and fibre for reinforcement, respectively. Different amounts of fine Al₂O₃–Y₂O₃ were added for liquid phase assisted sintering. For EPD, highly dispersed slurry was prepared by adjusting the zeta potentials of the constituent particles to ?+40 mV for homogeneous deposition. The composite properties were compared after using two different consolidation methods: hot pressing for 2 h at 20 MPa and spark plasma sintering (SPS) for 3 min at 45 MPa at 1750°C to minimise the damage to the SiC fibre. The maximum flexural strength and density for the 45 vol.-% fibre content composites were 482 MPa and 98% after hot pressing, respectively, whereas those for SPS were 561 MPa and 99·5%, indicating the effectiveness of SPS.     

A nitride whisker template for growth of mullite in SiC reticulated porous ceramics

Silicon carbide reticulated porous ceramics (SiC RPCs) were fabricated by polymer replica technique. The effects of nitride whisker template on the growth of mullite, the strut structure and mechanical properties of SiC RPCs were investigated. Prepolyurethane (PU) open-cell sponge was first coated by SiC slurry consisting of SiC, reactive Al₂O₃, microsilica and Si powder, then it was nitridized at 1400 °C in a flowing N₂ atmosphere to prepare SiC preforms. Subsequently, these preforms were treated by vacuum infiltration of alumina slurry and fired at 1450 °C in air. The results showed that Si₂N₂O whiskers grew on the surface and in the matrix of SiC preforms after nitridation. The diameter of struts in SiC RPCs increased after vacuum infiltration process because alumina slurry was easily adhered by the surface nitride whiskers. In addition, such whiskers inside the strut of SiC preforms acted as the template to promote the growth of column-liked mullite in SiC RPCs. The mechanical properties and thermal shock resistance of SiC RPCs were greatly improved due to the special interfacial characteristics of multi-layered struts as well as better interlocked column-liked mullite in SiC skeleton.     

Effects of Fe addition on the mechanical and thermo-mechanical properties of SiC/FeSi2/Si composites produced via reactive infiltration

Remaining silicon in SiC-based materials produced via reactive infiltration limits their use in high-temperature applications due to the poor mechanical properties of silicon: low fracture toughness, extreme fragility and creep phenomena above 1000 °C. In this paper SiC–FeSi₂ composites are fabricated by reactive infiltration of Si–Fe alloys into porous Cf/C preforms. The resulting materials are SiC/FeSi2 composites, in which remaining silicon is reduced by formation of FeSi₂. For the richest Fe alloys (35 wt% Fe) a nominal residual silicon content below 1% has been observed. However this, the relatively poor mechanical properties (bending strength) measured for those resulting materials can be explained by the thermal mismatch of FeSi2 and SiC, which weakens the interface and does even generate new porosity, associated with a debonding phenomenon between the two phases.     

Reactive infiltration processing of SiC/Fe–Si composites using preforms made of coked rice husks and SiC powder

A reactive infiltration processing of SiC/Fe–Si composites using preforms made of coked rice husks (RHs) and SiC powder in different ratios is reported, in which FeSi₂ alloy was used as infiltrant. The preforms were heat-treated at 1550 °C for 6 h prior to the infiltration. The coked RHs, which are composed of SiO₂ and C, were converted to SiC and poorly crystallized C by carbothermal reduction during the heat treatment. The study of the microstructure and mechanical properties of the composites shows that molten Fe–Si alloy had good wetting of the heat-treated preforms and adequate infiltration properties. Free carbon in the preform reacted with Si in the molten FeSi₂ during infiltration forming new SiC, the composition of the intermetallic liquid being moved towards that of FeSi. As a result, the infiltrated composites are composed of SiC, FeSi₂ and FeSi phases. Vickers hardness, elastic modulus, three-point flexural strength and indentation fracture toughness of the composites are found to increase with SiC additions up to 30% w/w in the preforms, reaching the values of 18.2 GPa, 290 GPa, 213 MPa and 4.9 MPa m^1/2, respectively. With the SiC addition further raised to 45% w/w, the elastic modulus, flexural strength and fracture toughness of the composite turned down probably due to high residual stress and hence the more intense induction of microcracks in the composite. De-bonding of SiC particles pulled out of the Fe–Si matrix, transgranular fracture of part of the SiC particles and in the Fe–Si matrix, and crack bridging all exist in the fracture process of the composites.     

Fatigue of three advanced SiC/SiC ceramic matrix composites at 1200°C in air and in steam

High‐temperature mechanical properties and tension‐tension fatigue behavior of three advanced SiC/SiC composites are discussed. The effects of steam on high‐temperature fatigue performance of the ceramic‐matrix composites are evaluated. The three composites consist of a SiC matrix reinforced with laminated, woven SiC (Hi‐Nicalon?) fibers. Composite 1 was processed by chemical vapor infiltration (CVI) of SiC into the Hi‐Nicalon? fiber preforms coated with boron nitride (BN) fiber coating. Composite 2 had an oxidation inhibited matrix consisting of alternating layers of silicon carbide and boron carbide and was also processed by CVI. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. Composite 3 had a melt‐infiltrated (MI) matrix consolidated by combining CVI‐SiC with SiC particulate slurry and molten silicon infiltration. Fiber preforms had a CVI BN fiber coating applied. Tensile stress‐strain behavior of the three composites was investigated and the tensile properties measured at 1200°C. Tension‐tension fatigue behavior was studied for fatigue stresses ranging from 80 to 160 MPa in air and from 60 to 140 MPa in steam. Fatigue run‐out was defined as 2 × 10⁵ cycles. Presence of steam significantly degraded the fatigue performance of the CVI SiC/SiC composite 1 and of the MI SiC/SiC composite 3, but had little influence on the fatigue performance of the SiC/SiC composite 2 with the oxidation inhibited matrix. The retained tensile properties of all specimens that achieved fatigue run‐out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated.     

Effects of CVI SiC amount and deposition rates on properties of SiCf/SiC composites fabricated by hybrid chemical vapor infiltration (CVI) and precursor infiltration and pyrolysis (PIP) routes

The SiC_f/SiC composites have been manufactured by a hybrid route combining chemical vapor infiltration (CVI) and precursor infiltration and pyrolysis (PIP) techniques. A relatively low deposition rate of CVI SiC matrix is favored ascribing to that its rapid deposition tends to cause a ‘surface sealing’ effect, which generates plenty of closed pores and severely damages the microstructural homogeneity of final composites. For a given fiber preform, there exists an optimized value of CVI SiC matrix to be introduced, at which the flexural strength of resultant composites reaches a peak value, which is almost twice of that for composites manufactured from the single PIP or CVI route. Further, this optimized CVI SiC amount is unveiled to be determined by a critical thickness t₀, which relates to the average fiber distance in fiber preforms. While the deposited SiC thickness on fibers exceeds t₀, closed pores will be generated, hence damaging the microstructural homogeneity of final composites. By applying an optimized CVI SiC deposition rate and amount, the prepared SiC_f/SiC composites exhibit increased densities, reduced porosity, superior mechanical properties, increased microstructural homogeneity and thus reduced mechanical property deviations, suggesting a hybrid CVI and PIP route is a promising technique to manufacture SiC_f/SiC composites for industrial applications.     

Design of refractory SiC/ZrSi2 composites: Wettability and spreading behavior of liquid Si-10Zr alloy in contact with SiC at high temperatures

Reactive infiltration of liquid Si-enriched alloys into C- or SiC-based preforms is a viable cost-less alternative to manufacture dense and highly performant SiC-based and MMC composites.In view to design and optimize liquid-assisted processes such as reactive infiltration, fundamental investigations on the interfacial phenomena occurring when the liquid Si-based alloys are in contact with C and SiC substrates, are crucial steps. In this context, targeted wettability studies may provide indications for predicting the key factors strongly influencing the reactive infiltration mechanisms, such as, unexpected interaction phenomena, etc. In particular, such preliminary experience may be helpful in finding the suitable set of operating conditions for fabricating tailored composites via reactive infiltration process.Aiming to “mimic’’ the conventional industrial processes for manufacturing SiC/ZrSi₂ refractory composites, the sessile drop method was applied to study the interfacial phenomena occurring at Si-10 % atZr/SiC interfaces over the temperature range of T =1360 °C-1450 °C.     

Pressureless sintering of ZrB2–SiC composite laminates using boron and carbon as sintering aids

Abstract

A processing method common to composite ceramics with very different ZrB₂/SiC ratios was developed in order to exploit ZrB₂–SiC laminates comprising alternate layers with different compositions for thermal protection systems of re-entry vehicles. Ceramic laminates were made using SiC, ZrB₂ and composites with a SiC/ZrB₂ ratio ranging from 100 vol.-%SiC to 100 vol.-%ZrB_2. The preparation was performed by tape casting of a slurry, layer stacking, debinding and pressureless sintering. Boron and carbon proved to be suitable sintering aids for SiC laminates as well as for composite laminates containing SiC. In the case of composites with a ZrB₂ matrix, the second phase of SiC acted as a sintering aid. This process obtains very similar densification for specimens with very different compositions (ranging from 100%SiC to 80ZrB₂–20SiC). The stiffness of ZrB₂–SiC laminates increased with the ZrB₂ content increase, while the bending strength was not affected by the ZrB₂/SiC ratio.     

Application of SiO2-coated SiC powder in stereolithography and sintering densification of SiC ceramic composites

Stereolithography additive manufacturing of SiC ceramic composites has received much attention. However, the forming efficiency and mechanical properties of their products need to be improved. This study aimed to prepare SiC ceramic composites with complex shapes and high flexural strength using a combination of digital light processing (DLP) and reactive solution infiltration process (RMI). A low-absorbance SiO₂ cladding layer was formed on the surface of SiC powder through a non-homogeneous precipitation process. With the densification of the cladding layer at high temperatures, SiO₂-coated SiC composite powder was used to formulate a photosensitive ceramic slurry with a solid content of 44 vol%. The resulting slurry exhibited a considerable improvement in curing thickness and rate and was used to mold ceramic green body with a single-layer slicing thickness of 100 μm using DLP. The ceramic blanks were then sintered and densified using a carbon thermal reduction combined with liquid silica infiltration (LSI) process, resulting in SiC ceramic composites with a density of 2.87 g/cm³ and an average flexural strength of 267.52 ± 2.5 MPa. Therefore, the proposed approach can reduce the manufacturing cycle and cost of SiC ceramic composites.     

Compressive strength and wear properties of SiC/Al6061 composites reinforced with high contents of SiC fabricated by pressure-assisted infiltration

Pressure-assisted infiltration was used to synthesize SiC/Al 6061 composites containing high weight percentages of SiC. A combination of PEG and glass water was used to fabricate SiC preforms and the effect of the presence of glass water on the microstructure and mechanical properties of the preforms was evaluated by performing compression tests on the preforms. Also, the compressive strength and the hardness of the SiC/Al composites were investigated. The results revealed that the glass water improved the compressive strength of the preforms by about five times. The microstructural characterization of the composites showed that the penetration of the aluminum melt into the preforms was completed and almost no porosity could be seen in the microstructures of the composites. Moreover, the composite containing 75 wt% SiC exhibited the highest compressive strength as well as the maximum hardness. The results of the wear tests showed that increasing the SiC content reduces the wear rate so that the Al-75 wt% SiC composite has a lower wear rate and a lower coefficient of friction than those of Al-67 wt% SiC composite. This indicated higher wear resistance in these composites than the Al alloy due to the formation of a tribological layer on the surface of the composites.     

Polymer-metal slurry reactive melt infiltration: A flexible and controllable ceramic modification strategy for irregular C/C components

Herein, we investigate the applicability of the polycarbosilane (PCS)–metal slurry reactive melt infiltration (RMI) process to various metals. The slurry exhibiting the best ceramized ability was used to examine the relationship between the ceramic thickness and reactive time, ceramic thickness and reactive temperature, and infiltration depth and slurry-coating thickness. The results show that the thickness of the ceramic layer increases with reactive time and temperature and the infiltration depth increases with the coating thickness. PCS–Si₉₀Zr₁₀ slurry RMI was selected to modify cylindrical nozzle C/C preforms, and dense C/C–SiC–ZrC composites with a density of ~2.05 g cm⁻³ were obtained. Owing to the good control of the PCS–Si₉₀Zr₁₀ slurry RMI on the interface, matrix, and carbon fiber of the as-received cylindrical composites, the bending strength of the C/C–SiC–ZrC composites was as high as 306.4 MPa, which is considerably higher than that of a C/C preforms (70.4 MPa). Considering the ablation resistance, the mass and linear ablation rates of the C/C–SiC–ZrC composite (~0.29 mg s⁻¹ and ~2.48 × 10⁻³ mm s⁻¹, respectively) were similar to those of the composites prepared using traditional RMI (~0.23 mg s⁻¹ and ~2.29 × 10⁻³ mm s⁻¹). The proposed polymer–metal RMI is more suitable for the modification of C/C preforms with thin-wall structures owing to its advantages including precise control of infiltration dose and flexible operation of slurry coating. Furthermore, it is suitable for the local modification of C/C components.     

Interaction of fiber matrix bonding in SiC/SiC ceramic matrix composites

Non-oxide ceramic matrix composites (CMC) based on SiC fibers with SiC matrix were fabricated by polymer infiltration and pyrolysis (PIP) and characterized regarding their microstructural features and their mechanical properties. The fiber preform was made using winding technology. During the winding process, the SiC fiber roving was impregnated by a slurry containing SiC powder and sintering additives (Y₂O_3, Al₂O₃ and SiO₂). This already helped to achieve a partial matrix formation during the preform fabrication. In this way, the number of PIP cycles to achieve composites with less than 10% open porosity could be reduced significantly. Additionally, damage-tolerant properties of the composites were obtained by an optimal design of the matrix properties although only uncoated fibers were used. Finally, composites with a strength level of about 500 MPa and a damage-tolerant fracture behavior with about 0.4% strain to failure were obtained.     

New advanced SiC-based composite materials for use in highly oxidizing environments: Synthesis of SiC/IrSi3

Currently, MMCs with SiC as reinforcement emerge as ideal candidates for long-term stable devices withstanding high temperatures and harsh operating environments which are typical for many industrial sectors, such as energy, aerospace, electronics, catalysis, etc. However, the costly manufacture of such composites is the major restraint to make them marketable.In this paper, highly-dense, nearly-shaped SiC/IrSi₃ composites effortless produced at T = 1250 °C under a vacuum by reactive melt infiltration of liquid Si-62 wt%Ir eutectic alloy into bimodal SiC_p-C porous preforms, are presented. The replacement of unreacted detrimental Si by a tougher and less oxidizing intermetallic phase (IrSi₃) was successfully obtained.     

Preparation and formation mechanism of C/C–SiC composites using polymer-Si slurry reactive melt infiltration

This study proposes a polymer-metal slurry reactive melt infiltration (RMI) method to overcome the limitations of conventional RMI in modifying irregular geometric carbon–carbon (C/C) preforms. Herein, polycarbosilane (PCS), polysiloxane, phenol-formaldehyde, and epoxy resin, which were introduced to prepare slurries with Si powder, and subsequently used to modify cylindrical C/C preforms into C/C–SiC composites. Results show that the PCS–Si slurry has the best RMI capability, by which, a cylindrical C/C preform (1.35 g·cm⁻³) was modified successfully to into a dense C/C–SiC composite (1.92 g·cm⁻³). PCS plays a vital role in fixing the coating to prevent it from falling off the surface of the C/C preform in PCS–Si slurry RMI. Both of the degree of densification and flexural strength of the C/C–SiC composites increase with an increase in the thickness of the PCS–Si slurry coating. The overreaction of the PCS–Si slurry RMI was effectively suppressed because the content of Si powder is reasonably controlled in the PCS–Si slurry coating. Moreover, nozzle-shaped C/C composites were successfully modified into a C/C–SiC composite for the first time using PCS–Si slurry RMI.     

Pressure‐less joining of C/SiC and SiC/SiC by a MoSi2/Si composite

A MoSi₂/Si composite obtained in situ by reaction of silicon and molybdenum at 1450°C in Ar flow is proposed as pressure‐less joining material for C/SiC and SiC/SiC composites. A new “Mo‐wrap” technique was developed to form the joining material and to control silicon infiltration in porous composites. MoSi₂/Si composite joining material infiltration inside coated and uncoated C/SiC and SiC/SiC composites, as well as its microstructure and interfacial reactions were studied. Preliminary mechanical strength of joints was tested at room temperature and after aging at service temperatures, resulting in interlaminar failure of the composites in most cases.     

On the effects of particle size and preform porosity on the mechanical properties of reaction-bonded boron carbide infiltrated with Al-Si alloy at 950 °C

The infiltration of boron carbide preforms with Al alloys at relatively low temperature prevents the formation of the undesired Al₄C₃ phase. In the present study the effect of boron carbide powder particle size on the mechanical properties and phase composition of composites infiltrated with Al-20%Si alloys at 950 °C was investigated. According to XRD analysis, the infiltrated composites contain Al₈C₇B₄, AlB₂ and AlB₁₂, as well as non-reacted Al and Si that originated from solidification of Al-Si alloy. The presence of small amounts of SiC was noted in specimens fabricated from fine boron carbide powder. No evidence for the formation of non-desired aluminum carbide phase was obtained. Infiltration of ceramic preforms with virtually the same green density generated composites with an elastic modulus and bending strength that continuously decreased from 270 GPa and 405 MPa to 195 GPa and 345 MPa for powder with 90% particles close to 3 μm and powder with 90% particles close to 180 μm, respectively. These results ambiguously confirm that boron carbide particle size strongly affects mechanical properties of reaction-bonded composites infiltrated with Al-Si alloy at 950 °C and reflect the amount of newly formed ceramic phases appearing during infiltration and the presence of defects at the metal-ceramic interface.