Properties of Cf/SiC-ZrB2-TaxCy composite produced by reactive hot pressing and polymer impregnation pyrolysis (RHP/PIP)

C_f/SiC-ZrB₂-Ta_xC_y composite was synthesized by reactive hot pressing (RHP) of C_f cloth, polycarbosilane (PCS), ZrB₂, and Ta powders at 4 MPa and 1200 °C. PIP cycle influenced sintering process by increasing density of the composite from 2.34 to 2.82 g/cc. Residual carbon produced during the PIP cycles at 1200 °C was utilized to yield Ta_xC_y by the addition of Ta. SEM images illustrate that by increasing the number of PIP cycles, SiC derived from the PCS cover the C_f fibre, micropores, and cracks. PIP cycles and Ta_xC_y phase improved flexural strength of the composite from 20 to 114 MPa. Mass and linear ablation resistance studies at 1600–2000 °C exhibited that oxide formation at the outer surface caused a barrier; further, no oxidation underneath the composite was observed. SEM images display that at 2000 °C, SiO₂ and Ta_xO_y were molten and sealed the pores. Hence, ablation resistance was enhanced by blocking the penetration in high-temperature flame.     

The degradation behavior of C/SiC composites fabricated by polymer impregnation and pyrolysis process under simulated space atomic oxygen environment

Carbon fiber reinforced silicon carbide (C/SiC) composites fabricated by polymer impregnation and pyrolysis (PIP) have been exposed in simulated space atomic oxygen (AO) environment for up to 15 h. The mechanical properties and chemical composition of PIP C/SiC composites have been studied. The results show that the mass loss of the composites increases at the beginning and then decreases as the exposure time lasts. The flexural properties of C/SiC composites have no obvious changes after up to 15 h exposure in AO. C/SiC composites have been oxidized slightly by AO. The amorphous carbon in the matrix has been oxidized to CO or CO₂ gas and SiC has been oxidized to SiO gas and SiO₂.     

Fabrication of tough SiCf/SiC composites by electrophoretic deposition using a fabric coated with FeO-catalyzed phenolic resin

A hybrid processing route based on vacuum infiltration, electrophoretic deposition, and hot-pressing was adopted to fabricate dense and tough SiC_f/SiC composites. The as-received Tyranno SiC fabric preform was infiltrated with phenolic resin containing 5 wt.% FeO and SiC powders followed by pyrolysis at 1700 °C for 4 h to form an interphase. Electrophoretic deposition was performed to infiltrate the SiC-based matrix into the SiC preforms. Finally, SiC green tapes were sandwiched between the SiC fabrics to control the volume fraction of the matrix. Densification close to 95% ρ_theo was achieved by incorporating 10 wt.% Al₂O₃-Sc₂O₃ sintering additive to facilitate liquid phase sintering at 1750 °C and 20 MPa for 2 h. X-ray diffraction and Raman analyses confirmed the catalytic utility of FeO by the formation of a pyrolytic carbon phase. The flexural response was explained in terms of the extensive fractography results and observed energy dissipating modes.     

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.     

Processing and mechanical performance of 3D Cf/SiCN composites prepared by polymer impregnation and pyrolysis

The processing of 3D carbon fiber reinforced SiCN ceramic matrix composites prepared by polymer impregnation and pyrolysis (PIP) route was improved, and factors that determined the mechanical performance of the resulting composites were discussed. 3D C_f/SiCN composites with a relative density of ∼81% and uniform microstructure were obtained after 6 PIP cycles. The optimum bending strength, Young's modulus and fracture toughness of the composites were 75.2 MPa, 66.3 GPa and 1.65 MPa m^1/2, respectively. The residual strength retention rate of the as-pyrolyzed composites was 93.3% after thermal shock test at ΔT = 780 °C. It further degraded to 14.6% when the thermal shock temperature difference reached to 1180 °C. The bending strength of the composites was 35.6 MPa after annealing at 1000 °C in static air. The deterioration of the bending strength should be attributed to the strength degradation of carbon fibers and decomposition of interfacial structure.     

Fabrication of the tube-shaped SiCf/SiC by hot pressing

A manufacturing technique for fabricating a dense tubular SiC long fiber-reinforced SiC composite (SiC_f/SiC) by hot pressing was developed. After infiltrating a SiC-based matrix phase, containing a 12 wt% of Al₂O₃–Y₂O₃ sintering additive, into the fine voids of a Tyranno^TM-SA3 SiC fabric preform by electrophoretic deposition combined with the application of ultrasonic pulses, hot pressing was performed using 2 types of specially designed molds filled with graphite powder to transfer the vertical hot press force efficiently to the sidewalls of the tubular SiC_f/SiC. Compared to the low density (~60%) of SiC_f/SiC hot-pressed using a conventional mold, a density >95% could be acquired using a special mold filled with graphite powder as a pressure delivering medium. This method is suitable for fabricating a dense tubular SiC_f/SiC, which cannot be obtained using a conventional extrusion method.     

Microstructure and mechanical properties of boron carbide/graphene nanoplatelets composites fabricated by hot pressing

In this study, boron carbide (B₄C)-graphene nanoplatelets (GNPs) composites, with enhanced strength and toughness, were fabricated by hot pressing at 1950 °C under a pressure of 30 MPa for 1 h. Microstructure analysis revealed that the GNPs are homogenously dispersed within the B₄C matrix. Raman spectroscopy and electron microscopy showed the orientation of the GNPs in the composites. The effects of the amount of GNPs on the microstructure and mechanical properties of the composites were also investigated. The optimal mechanical properties were achieved using 1 wt% GNPs. The relative density, Vickers hardness, flexure strength, and fracture toughness of the B₄C-GNPs composite ceramic were found to be 99.12%, 32.8 GPa, 508 MPa, and 4.66 MPa m^1/2, respectively. The main toughening mechanisms included crack deflection in three dimensions, GNPs pull-out, and crack bridging. The curled and semi-wrapped GNPs encapsulated individual B₄C grains to resist GNPs pull-out and to deflect propagating cracks.     

Mechanical characteristics of porous hydroxyapatite/oxide composites produced by post-sintering hot isostatic pressing

Porous hydroxyapatite and hydroxyapatite/oxide composites, with 10 wt% addition of Y₂O₃, ZrO₂ or TiO₂ have been prepared by hot isostatic pressing after pressureless sintering, and their phase composition, mechanical properties and microstructure investigated. The quantitative X-ray diffraction analyses reveal that the addition of Y₂O₃ inhibits the hydroxyapatite decomposition completely during the consolidation processes as a result of the Y ion dissolution into the hydroxyapatite lattice. On the contrary, it is found that the addition of ZrO₂ or TiO₂ enhances the decomposition of hydroxyapatite into Ca₃(PO₄)₂, which causes the transformation of the starting oxides. The mechanical characterization of the materials has been accomplished by three-point flexure tests, and nanoindentation and microhardness measurements. Post-sintering hot isostatic pressed pure hydroxyapatite, which resulted in a porous biphasic material with 13.2 wt% β-Ca₃(PO₄)₂, exhibited the best mechanical properties. The failure of hydroxyapatite-10Y₂O₃ during the flexure tests was no catastrophic in contrast to the catastrophic behaviour found in the other materials.     

Significance of modification of slurry infiltration process for the precursor impregnation and pyrolysis process of SiCf/SiC composites

Several intermediate steps were applied before the precursor infiltration and pyrolysis process to improve the infiltration of SiC slurry for promoting the infiltration of SiC slurry into fiber voids. These steps include sonication, popping, electrophoretic deposition, vacuum infiltration and cold isostatic pressing (CIP). The intermediate processes, especially popping and CIP, had a beneficial effect on green density enhancement and improving the homogeneous infiltration of the slurry into fiber fabrics. The density of the SiC_fiber/SiC_filler green body was 2.20 g/cm³, which corresponded to 68 % of relative density. The SiC_f/SiC composite has a high density of 2.65 g/cm³ after seven PIP cycles.     

The fabrication and mechanical properties of SiC/SiC composites prepared by SLS combined with PIP

Traditionally, SiC components with complex shapes are very difficult or even impossible to fabricate. This paper aims to develop a new manufacturing process, combining selective laser sintering (SLS), cold isostatic pressing (CIP) and polymer infiltration pyrolysis (PIP), to manufacture complex silicon carbide parts and improve the mechanical properties of silicon carbide ceramic parts. The density and porosity of SiC/SiC composites were measured. Furthermore, the mechanical properties of the specimens with cold isostatic pressing and the specimens without cold isostatic pressing were compared. The bending strength of the specimens with cold isostatic pressing was 201?MPa, and the elastic modulus was 1.27?GPa. And, the bending strength of the specimens without cold isostatic pressing was 142?MPa, and the elastic modulus was 0.88?GPa. Increasing the density of SiC/SiC can enhance the mechanical properties of SiC/SiC composites.     

Preparation and properties of C/SiC/ZrO2 porous composites by hot isostatic pressing the pyrolyzed preforms

Three phase mixture of C/SiC/ZrO₂ porous composites were prepared from commercially available phenolic resin, Si and ZrO₂ powders. In the first step, mixed powders were pyrolyzed at 850 °C in vacuum to obtain a carbonized microporous material and then hot isostatically pressed at 1200, 1300 and 1350 °C for 10 min in an argon pressure of 50 MPa to prepare C/SiC/ZrO₂ porous composites, in second step. The hot isostatic pressing led to the increase in density from 3.28 to 3.48 g/cm³ and reduction in porosity (from 32 to 20%) of the composites. X-ray diffraction analyses revealed the existence of β-SiC and carbon might be amorphous in the composites. According to the results of scanning electron microscopy, the crystal growth of β-SiC with facets was observed at 1350 °C. In addition, the energy dispersive spectroscopy showed that carbon/silicon atomic ratio was 1:1 in the crystals. X-ray photoelectron spectroscopy of the composites suggested that evolved gaseous molecules, due to the decomposition of phenolic resin, reacted with molecules containing Si to form β-SiC. The formation and growth of β-SiC in addition to the densification of matrix by hot isostatic pressing led to the increase in hardness (max.: 13.99 GPa) at higher temperatures.     

Low-surface-temperature jump behavior of C/SiC composites prepared via precursor impregnation and pyrolysis in high-enthalpy plasma flows

The response of C/SiC composites prepared via precursor impregnation and pyrolysis was investigated in a 1 MW plasma wind tunnel. Under a considerable aero heating of up to 26.2 MJ/kg of specific total enthalpy, the samples were exposed to heat fluxes exceeding 5.7 MW/m² and low pressures of 4.5–6.6 kPa. The samples were able to withstand low heat fluxes and low stagnation pressures, and their carbon-rich nature improved the thermal conductivity, presenting a low steadystate surface temperature. However, a spontaneous jump in the surface temperature at around 1700 °C was observed at high heat fluxes and high stagnation pressures. The jump temperature was lower compared with that reported in previous studies, and was found to increase rapidly to temperatures above 2000 °C. This low-temperature jump phenomenon was associated with the evolution of microstructure during testing, and the underlying mechanism was revealed through the use of thermodynamics analysis.     

Properties and microstructure evolution of Cf/SiC composites fabricated by polymer impregnation and pyrolysis (PIP) with liquid polycarbosilane

In the present study, a novel liquid polycarbosilane (LPCS) with a ceramic yield as high as 83% was applied to develop 3D needle-punched C_f/SiC composites via polymer impregnation and pyrolysis process (PIP). The cross-link and ceramization processes of LPCS were studied in detail by FT-IR and TG-DSC; a compact ceramic was obtained when LPCS was firstly cured at 120 °C before pyrolysis. It was found that the LPCS-C_f/SiC composites possessed a higher density (2.13 g/cm³) than that of the PCS-C_f/SiC composites even though the PIP cycle for densification was obviously reduced, which means a higher densification efficiency. Logically, the LPCS-C_f/SiC composites exhibited superior mechanical properties. The shorter length and rougher surfaces of pulled-out fibers indicated the LPCS-C_f/SiC composites to possess a stronger bonding between matrix and PyC interphase compared with the PCS-C_f/SiC composites.     

Manufacturing of ceramic matrix composite using a hybrid process combining TiSi2 active filler infiltration and preceramic impregnation and pyrolysis

The manufacturing of silicon carbide reinforced ceramic matrix composites by a hybrid process is explored. Fibre preforms are infiltrated with TiSi₂ powders using the slurry method. Using TiSi₂ active filler leads to reduce the porosity by the subsequent formation of nitride phases after treatment under N₂ atmosphere at low temperatures (≤1100 °C). Taking into account the influence of the specific surface area of the powder on the nitridation rate, it is shown that it is possible to produce nitrides TiN and Si₃N₄ at 1100 °C with an interesting volume expansion inside the composite. To complete the densification of the composite, a polymer impregnation and pyrolysis (PIP) process are performed with a liquid polymeric precursor. Characterizations of the composites show that mechanical properties are improved with the presence of the TiN and Si₃N₄ phases, and the number of PIP cycles.     

Effect of processing technology on structural stability of SiC/SiBCZr ceramic matrix composites

SiC/SiBCZr composites were prepared through polymer impregnation and pyrolysis process using the second generation SiC fibers as raw material. The effects of surface substrate removal, secondary densification, and deposition coating on the structure, mechanical properties, and high temperature stability of SiC/SiBCZr composites were investigated. Results showed that the porosity of SiC/SiC composites could be greatly diminished by the optimized treatment process, and the surface of SiC/SiBCZr composites is uniformly filled into the pores by β-SiC particles, thereby achieving the sealing effect. Meanwhile, the as-prepared SiC/SiBCZr composites had excellent high temperature structural stability. At the later stage of oxidation reaction, borosilicate oxidation products with moderate fluidity, fluid lava form and self repairing function generated from ceramic matrix can effectively inhibit the oxidation reaction and improve the high temperature structural stability of SiC/SiBCZr composites. The above-mentioned high temperature structural stability provided the foundation and technical support for improving the service life and expanding the application of SiC/SiBCZr composites.     

Fabrication of tubular SiCf/SiC using different preform architectures by electrophoretic deposition and hot pressing

This paper reports the processing feasibility of electrophoretic deposition combined with hot pressing in the fabrication of dense tubular SiC_f/SiC composites using a cylindrical mold. A simulation of pressure distribution using ANSYS software was performed by varying the angular inclinations in a cylindrical mold with an ‘out → in’ configuration so as to ensure a maximum and uniform conversion of vertical hot press force to the lateral side of a centrally-located preform through graphite powder. The simulation revealed an inhomogeneous pressure distribution along the height of the preform, which could be minimized by mold optimization to achieve a more uniform tube density. To verify this, two different preform architectures such as 0/90° woven 2-D fabric rolled in a jelly state and filament winding with two plies having an inter-ply angle of 55° were hot-pressed using a mold fabricated based on the simulation after infiltrating the matrix phase by electrophoretic deposition. The density of the tube could be increased with more uniform microstructures. Although the tube using a filament winding preform exhibited a lower flexural strength (105 MPa) and relative density (90%) than those with the preform rolled in a jelly state (221 MPa, 95%), the results revealed a high degree of fiber pull-out due to the PyC coating on the SiC fiber.     

有机前驱体中添加ZrB2和SiC微粉制备Cf/SiC-ZrB2复合材料

通过在有机前驱体溶液中加入惰性填料ZrB_2和SiC微粉,制备了C_f/SiC-ZrB_2复合材料。分别研究了三组不同含量的料浆对复合材料浸渍裂解效果的影响,并借助扫描电镜(SEM)和能谱分析(EDS)对制备的Cf/SiC-ZrB2复合材料的微观结构和元素组成进行了分析。研究表明:在有机前驱体溶液中添加无机粉体浸渍复合材料能够起到缩短制备周期、提高材料强度的目的。当加入惰性填料的质量分数为15%时,能够在8个制备周期内将复合材料的密度快速提升到2.0g?cm~(-3),而且制备的材料内部结构致密,力学性能优异。     

Effect of in situ grown SiC nanowires on microstructure and mechanical properties of C/SiC composites

Hexagonal-shaped SiC nanowires were in situ formed in C/SiC composites with ferrocene as catalyst in the densification process of polymer impregnation and pyrolysis. The effect of SiC nanowires on microstructure and properties of the composites were studied. The results show that the in situ formed SiC nanowires were hexagonal, mostly with diamer of about 250 nm, and grew by the vapor–liquid–solid (VLS) mechanism. The C/SiC composite with nanowires shows higher bulk density and flexural strength than the one with no SiC nanowires, and the high temperature flexural strength behavior of C/SiC composites with SiC nanowires was evaluated.     

Enhanced phase stability in hydroxylapatite/zirconia composites with hot isostatic pressing

Hydroxylapatite (HA) composites with pure zirconia (ZrO₂), and 3 and 8% Y₂O₃ doped ZrO₂ were pressure-less sintered in air and hot isostatically pressed (under 120 MPa gas pressure) at 1100 °C for 2 h. The reactions and phase transformations were monitored by X-ray diffraction, thermal analysis, and Raman spectroscopy. HA/pure ZrO₂ composites were not thermally stable in air sintering; HA dissociated into α and β tricalcium phosphate while monoclinic ZrO₂ was transformed into tetragonal and cubic phases. No decomposition in HA or phase transformation in ZrO₂ were observed in hydroxylapatite/3% Y₂O₃ doped ZrO₂ or HA/8% Y₂O₃ doped ZrO₂ composites. On the other hand, HA and ZrO₂ phases in hot isostatically pressed composites remained stable. The highest densification was found in a composite initially containing 10% monoclinic ZrO₂ among the composites sintered in air. The densification of the composites decreased at lower sintering temperatures and higher ZrO₂ contents upon air-sintering. The HIPped composites were densified to about 99.5% of theoretical densities in all mixing ratios. The reactivity between ZrO₂ and HA was dependent on the amount of air in the sintering environment. Hot isostatic pressing with very limited retained air was proved to be a very convenient method to insure both phase stability and full densification during the production of hydroxylapatite zirconia composites.     

Densification of MCMB–SiC composites via two-step hot pressing

Mesocarbon microbead–SiC (MCMB–SiC) composites with 30 wt% MCMBs were densified using a two-step hot pressing method. Based on the pyrolysis of the initial MCMB powders, the effects of the pressing schedule on densification were investigated and the optimal first-step pressing temperature was determined. To reveal the influence of temperature on their microstructures, the raw MCMB powders were heat-treated at different temperatures in the range 400–1400 °C. The morphologies and degrees of carbonisation at different temperatures were additionally studied. The results showed that densification was mainly affected by the micro-gaps in the lamellar structure formed during the pyrolysis of the MCMBs. When the samples were first hot-pressed at a lower temperature and then at a higher temperature, the densification pressure required was effectively decreased. Furthermore, when the samples were first pressed at an appropriate temperature, the relative density of the composites was improved to a rather high value of 98.6%. The two-step hot pressing method was effective in fabricating dense C–SiC composites with high C content.