Low temperature fabrication of Cf/BNi/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiCm high entropy ceramic matrix composite by slurry coating and laminating combined with precursor infiltration and pyrolysis

In this study, the low temperature fabrication of a C_f/BN_i/(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C-SiC_m high entropy ceramic (HEC) ceramic matrix composite (CMC) was achieved through slurry coating and laminating (SCL) combined with precursor infiltration and pyrolysis (PIP). Firstly, the (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C HEC powder was synthesized by pressureless sintering and ball milling. Then, a C_f/BN_i/HEC_m CMC preform was obtained by the SCL process. At last, the composite was densified by PIP of SiC at 1200 °C and a C_f/BN_i/HEC-SiC_m CMC was the final result. The density and open porosity of the HEC-CMC were 2.7 g/cm³ and 10%, respectively. The composite had a relatively high flexural strength (269 ± 25 MPa) and flexural modulus (53.3 ± 7.9 GPa). Fiber degradation was scarcely detected and fiber pullout was clearly observed. Most importantly, the fabrication method is simple and the fabrication temperature is rather low. This study opens a new insight for high entropy ceramic matrix composites fabrication.     

Additive manufacturing of continuous carbon fiber reinforced high entropy ceramic matrix composites via paper laminating,direct slurry writing,and precursor infiltration and pyrolysis

In this study, continuous carbon reinforced C_f/(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C–SiC high entropy ceramic matrix composites were additively manufactured through paper laminating (PL), direct slurry writing (DSW), and precursor infiltration and pyrolysis (PIP). (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C high entropy ceramic (HEC) powders were synthesized by pressureless sintering and ball milling. A certain proportion of HEC powder, SiC powder, water, binder, and dispersant were mixed to prepare the HEC-SiC slurry. Meanwhile, BN coating was prepared on the 2D fiber cloth surface by the boric acid-urea method and then the cloth was cut into required shape. Additive manufacturing were conducted subsequently. Firstly, one piece of the as-treated carbon fiber cloth was auto-placed on the workbench by paper laminating (PL). Then, the HEC-SiC slurry was extruded onto the surface of the cloth by direct slurry writing (DSW). PL and DSW process were repeated, and a C_f/HEC-SiC preform was obtained after 3 cycles. At last, the preform was densified by precursor infiltration and pyrolysis (PIP) and the final C_f/HEC-SiC composite was prepared. The open porosity of the C_f/HEC-SiC composites, with the HEC volume fractions of 15, 30 and 45%, were 7.7, 10.6, and 11.3%, respectively. And the density of the C_f/HEC-SiC composites, with the HEC volume fractions of 15, 30 and 45%, were 2.9, 2.7 and 2.3 g/cm³, respectively. The mechanical properties of the C_f/HEC-SiC composites increased firstly and then decreased with the HEC content increase, reaching the maximum value when the HEC volume fraction was 30%. The mechanical properties of the C_f/HEC-SiC composites containing 45, 30 and 15% HEC were as follows: flexural strength (180.4 ± 14 MPa, 183.7 ± 4 MPa, and 173.9 ± 4 MPa), fracture toughness (11.9 ± 0.17 MPa m^1/2, 14.6 ± 2.89 MPa m^1/2, and 11.3 ± 1.88 MPa m^1/2), and tensile strength (71.5 ± 4.9 MPa, 98.4 ± 12.2 MPa, and 73.4 ± 8.5 MPa). From this study, the additive manufacturing of continuous carbon fiber reinforced high entropy ceramic matrix composites was achieved, opening a new insight into the manufacturing of ceramic matrix composites.     

Effects of in-situ carbon layer and volume fraction of SiC fiber on the mechanical properties and fracture behaviors of SiCf/SiC composites fabricated by a modified PIP method

Unidirectional SiC_f/SiC composites (UD SiC_f/SiC composites) with excellent mechanical properties were successfully fabricated by a modified PIP method which involved the preparation of film-like matrix containing carbon layer with a low concentration PCS solution followed by the rapid densification of composites with a high concentration PCS solution. Carbon layers were in-situ formed and alternating with SiC layers in the as-received matrix. The unique microstructure endows the composites with appropriate interfacial bonding state, good load transfer ability of interphase and matrix and load bearing ability of fiber, and great crack deflection capacity, which ensures the synergy of high strength and toughness of composites. It is also found that the fiber volume fraction in the preform makes a non-negligible effect on the distribution of interphase and matrix, of which the reasonable adjustment can be utilized to optimize the mechanical properties of composites. Compared with the composites only using high concentration PCS solution, the UD SiC_f/SiC composites prepared by the modified PIP method exhibit superior mechanical properties. Ultrahigh flexural strength of 1318.5 ± 158.3 MPa and fracture toughness of 47.6 ± 5.6 MPa·m^1/2 were achieved at the fiber volume fraction of 30%.     

The mechanical,thermophysical and electromagnetic properties of UD SiCf/SiC composites in different directions

Unidirectional (UD) silicon carbide (SiC) fiber-reinforced SiC matrix (UD SiC_f/SiC) composites with CVI BN interphase were fabricated by polymer infiltration-pyrolysis (PIP) process. The effects of the anisotropic distribution of SiC fibers on the mechanical properties, thermophysical properties and electromagnetic properties of UD SiC_f/SiC composites in different directions were studied. In the direction parallel to the axial direction of SiC fibers, SiC fibers bear the load and BN interphase ensures the interface debonding, so the flexural strength and the fracture toughness of the UD SiC_f/SiC composites are 813.0 ± 32.4 MPa and 26.1 ± 2.9 MPa·m^1/2, respectively. In the direction perpendicular to the axial direction of SiC fibers, SiC fibers cannot bear the load and the low interfacial bonding strengths between SiC fiber/BN interphase (F/I) and BN interphase/SiC matrix (I/M) both decrease the matrix cracking stress, so the corresponding values are 36.6 ± 6.9 MPa and 0.9 ± 0.5 MPa?m^1/2, respectively. The thermal expansion behaviors of UD SiC_f/SiC composites are similar to those of SiC fibers in the direction parallel to the axial direction of SiC fibers, and are similiar to those of SiC matrix in the direction perpendicular to the axial direction of SiC fibers. The total electromagnetic shielding effectiveness (EM SE_T) of UD SiC_f/SiC composites attains 32 dB and 29 dB when the axial direction of SiC fibers is perpendicular and parallel to the electric field direction, respectively. The difference of conductivity in different directions is the main reason causing the different SE_T. And the dominant electromagnetic interference (EMI) shielding mechanism is absorption for both studied directions.     

Construction of compound interface in SiCf/mullite ceramic-matrix composites for enhanced mechanical and microwave absorbing performance

SiC fiber-reinforced mullite ceramic-matrix (SiC_f/mullite) composite is a promising load-bearing and microwave absorption material. However, the strong interfacial bonding strength and low permittivity cause poor mechanical and absorption performance. Herein, we report SiC_f/C-SiC/mullite composite containing a carbon nanosphere network (CNSN) in the SiC interface prepared by precursor infiltration and pyrolysis (PIP). Due to the contribution of CNSN towards interface debonding, fiber slipping, and individual fiber pull-out, the composite shows significant improvement in the flexural strength (by 187%, from 56.23 ± 4.89 MPa to 161.69 ± 13.43 MPa) and the failure displacements (by 238%, from 0.080 ± 0.006 mm to 0.271 ± 0.015 mm). Moreover, the real and imaginary parts of complex permittivity (ε′, ε″) are enhanced from 5.57 to 5.98–6.36–7.11 and from 1.27 to 1.95–2.97–4.69, respectively. Under the synergistic effect of appropriate impedance matching in company with effective conductive loss and multiple polarization loss, the effective absorption bandwidth (EAB) increases from 0.98 GHz to the entire X band, and the minimum reflection loss (RL_min) enhanced from − 14.31 dB to − 41.51 dB.     

Microstructure and mechanical properties of quasi-isotropic chopped fiber-reinforced PyC–SiC matrix composite prepared by novel nondamaging method

In this work, quasi-isotropic chopped carbon fiber-reinforced pyrolytic carbon and silicon carbide matrix (C_f/C–SiC) composites and chopped silicon carbide fiber-reinforced silicon carbide matrix (SiC_f/SiC) composites were prepared via novel nondamaging method, namely airlaid process combined with chemical vapor infiltration. Both composites exhibit random fiber distribution and homogeneous pore size. Young's modulus of highly textured pyrolytic carbon (PyC) matrix is 23.01 ± 1.43 GPa, and that of SiC matrix composed of columnar crystals is 305.8 ± 9.49 GPa in C_f/C–SiC composites. Tensile strength and interlaminar shear strength of C_f/C–SiC composites are 52.56 ± 4.81 and 98.16 ± 24.62 MPa, respectively, which are both higher than those of SiC_f/SiC composites because of appropriate interfacial shear strength and introduction of low-modulus and highly textured PyC matrix. Excellent mechanical properties of C_f/C–SiC composites, particularly regarding interlaminar shear strength, are due to their quasi-isotropic structure, interfacial debonding, interfacial sliding, and crack deflection. In addition to the occurrence of crack deflection at the fiber/matrix interface, crack deflection in C_f/C–SiC composites takes also place at the interface between PyC–SiC composite matrix and the interlamination of multilayered PyC matrix. Outstanding mechanical properties of as-prepared C_f/C–SiC composites render them potential candidates for application as thermal structure materials under complex stress conditions.     

Effect of high-temperature heat treatment on the microstructure and mechanical behavior of PIP-based C/C-SiC composites with SiC filler

C/C-SiC composites were fabricated by a combined process of chemical vapor deposition (CVD), slurry infiltration(SI), and precursor infiltration and pyrolysis (PIP). The microstructure and mechanical behavior were investigated for the dense C/C-SiC composites before and after high-temperature heat treatment. The results indicated that the sintering of the SiC matrix and the migration of the SiC matrix/fiber bundles weak interface occurred after high-temperature heat treatment at 1900 ℃. The SiC sintering resulted in an increase in the flexural strength of the C/C-SiC composites from 298.9 ± 35.0 MPa to 411.1 ± 57.3 MPa. The migration of the weak interface changed the direction of crack propagation, making the fracture toughness of the C/C-SiC composites decrease from 13.3 ± 1.7 MPa⋅m ^1/2 to 9.02 ± 1.5 MPa⋅m ^1/2.     

Mechanical properties of silicon carbide—in situ zirconium carbonitride composites

SiC–Zr₂CN composites were fabricated by conventional hot pressing from β-SiC and ZrN powders with 2 vol% equimolar Y₂O₃–Sc₂O₃ as a sintering additive. The effects of the ZrN addition on the room-temperature (RT) mechanical properties and high-temperature flexural strength of the SiC–Zr₂CN composites were investigated. The fracture toughness gradually increased from 4.2 ± 0.3 MPa·m^1/2 for monolithic SiC to 6.3 ± 0.2 MPa·m^1/2 for a SiC–20 vol% ZrN composite, whereas the RT flexural strength (546 ± 32 MPa for the monolithic SiC) reached its maximum of 644 ± 87 MPa for the SiC–10 vol% ZrN composite. The monolithic SiC had improved strength at 1200°C, whereas the SiC–Zr₂CN composites could not retain their RT strengths at 1200°C. The typical flexural strength values of the SiC–0, 10, and 20 vol% ZrN composites at 1200°C were 650 ± 53, 448 ± 31, and 386 ± 19 MPa, whereas their RT strength values were 546 ± 32, 644 ± 87, and 528 ± 117 MPa, respectively.     

Fabrication and properties of Cf/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-SiC high-entropy ceramic matrix composites via precursor infiltration and pyrolysis

In this work, C_f/(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C-SiC high-entropy ceramic matrix composites were reported for the first time. Based on the systematic study of the pyrolysis and solid-solution mechanisms of (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C precursor by Fourier transform infrared spectroscopy, TG-MS and XRD, C_f/(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C-SiC with uniform phase and element distribution were successfully fabricated by precursor infiltration and pyrolysis. The as-fabricated composites have a density and open porosity of 2.40 g/cm³ and 13.32 vol% respectively, with outstanding bending strength (322 MPa) and fracture toughness (8.24 MPa m^1/2). The C_f/(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C-SiC composites also present excellent ablation resistant property at a heat flux density of 5 MW/m², with linear and mass recession rates of 2.89 μm/s and 2.60 mg/s respectively. The excellent combinations of mechanical and ablation resistant properties make the C_f/(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C-SiC composites a new generation of reliable ultra-high temperature materials.     

Enhanced high-temperature strength in textured (Ti1/3Zr1/3Hf1/3)B2 medium-entropy ceramics via strong magnetic field

This study prepared textured (Ti_1/3Zr_1/3Hf_1/3)B₂ medium-entropy ceramics for the first time that maintain enhanced flexural strength up to 1800°C using single-phase (Ti_1/3Zr_1/3Hf_1/3)B₂ powders, slip casting under a strong magnetic field, and hot-pressed sintering methods. Effects of WC additive and strong magnetic field direction on the phase compositions, orientation degree, microstructure evolution, and high-temperature flexural strength of (Ti_1/3Zr_1/3Hf_1/3)B₂ were investigated. (Ti_1/3Zr_1/3Hf_1/3)B₂ grain grows along the a,b-axes, resulting in a platelet-like morphology. Pressure parallel and perpendicular to the magnetic field direction can promote the orientation degree and hinder the texture structure formation, respectively. Reaction products of W(B,C) and (Ti,Zr,Hf)C between (Ti_1/3Zr_1/3Hf_1/3)B₂ and WC additive can efficiently refine the (Ti_1/3Zr_1/3Hf_1/3)B₂ grain size and promote grain orientation. (Ti_1/3Zr_1/3Hf_1/3)B₂ ceramics doped with 5 vol.% WC yielded a Lotgering orientation factor of 0.74 through slip casting under a strong magnetic field (12 T) and hot-pressed sintering at 1900°C. Furthermore, cleaning the boundary by W(B,C) and introducing texture can enhance the grain-boundary strength and improve its high-temperature flexural strength. The four-point flexural strength of textured (Ti_1/3Zr_1/3Hf_1/3)B₂-5 vol.% WC ceramics was 770 ± 59 MPa at 1600°C and 638 ± 117 MPa at 1800°C.     

Temperature-dependent elastic and thermodynamic properties of ZrC,HfC, and their solid solutions (Zr0.5Hf0.5)C

Zirconium carbide (ZrC) and hafnium carbide (HfC) have been identified as ultrahigh temperature ceramics with excellent thermal conductivity performance. The temperature profiles of ZrC and HfC have been studied; however, the temperature-dependent of solid solution of (Zr_0.5Hf_0.5)C is still lacking. Herein, we report the temperature-dependent elastic and thermodynamic properties of (Zr_0.5Hf_0.5)C using first-principles calculations. The covalent characters of ZrC, HfC, and (Zr_0.5Hf_0.5)C are weakened at high temperatures by analyzing their respective electronic structures. In addition, the equilibrium volumes at different temperatures can be determined from the energy–volume (E–V) curves under the quasi-harmonic approximation. Throughout the temperature ranges studied, the HfC material shows the highest bulk modulus and lowest thermal expansion. When T > 1000 K, (Zr_0.5Hf_0.5)C exhibits better shear and Young's modulus performance close to HfC and shows the highest anisotropy. The lattice thermal conductivity decreased as temperature increased for ZrC, HfC, and (Zr_0.5Hf_0.5)C, and (Zr_0.5Hf_0.5)C has the smallest lattice thermal conductivity. These results provide fundamental and useful information for the practical application of ZrC, HfC, and (Zr_0.5Hf_0.5)C.     

Methane combustion over Pd/ZrO2/SiC,Pd/CeO2/SiC,and Pd/Zr0.5Ce0.5O2/SiC catalysts

The performances of different promoters (CeO₂, ZrO₂ and Ce_0.5Zr_0.5O₂ solid solution) modified Pd/SiC catalysts for methane combustion are studied. XRD and XPS results showed that Zr⁴⁺ could be incorporated into the CeO₂ lattice to form Zr_0.5Ce_0.5O₂ solid solution. The catalytic activities of Pd/CeO₂/SiC and Pd/ZrO₂/SiC are lower than that of Pd/Zr_0.5Ce_0.5O₂/SiC. The Pd/Zr_0.5Ce_0.5O₂/SiC catalyst can ignite the reaction at 240 °C and obtain a methane conversion of 100% at 340 °C, and keep 100% methane conversion after 10 reaction cycles. These results indicate that active metallic nanoparticles are well stabilized on the SiC surface while the promoters serve as oxygen reservoir and retain good redox properties.     

Thermal and Mechanical Properties of SiC–TiC0.5N0.5 Composites

SiC–TiC_0.5N_0.5 composites were fabricated from β‐SiC and TiN powders with 2 vol% equimolar Y₂O₃–Sc₂O₃ additives by conventional hot pressing. Thermal and mechanical properties of the SiC–TiC_0.5N_0.5 composites were investigated as a function of initial TiN content. Relative densities of ≥98.9% were achieved for all samples. The addition of a small amount of TiN increased thermal conductivity, flexural strength, and fracture toughness of SiC ceramics. However, further addition of TiN in excess of 10 and 20 vol% deteriorated both thermal conductivity and flexural strength of the composites, respectively. In contrast, the fracture toughness of the composites increased continuously from 4.2 to 6.2 MPa?m^1/2 with increasing initial TiN content from 0 to 35 vol%, due to crack deflection by TiC_0.5N_0.5. The maximum values of thermal conductivity and flexural strength were 224 W/m K for a 2 vol% TiC_0.5N_0.5 and 599 MPa for a 10 vol% TiC_0.5N_0.5 composite.     

Effect of PyC interphase thickness on mechanical and ablation properties of 3D Cf/ZrC–SiC composite

Three-dimensional (3D) C_f/ZrC–SiC composites were successfully prepared by the polymer infiltration and pyrolysis (PIP) process using polycarbosilane (PCS) and a novel ZrC precursor. The effects of PyC interphase of different thicknesses on the mechanical and ablation properties were evaluated. The results indicate that the C_f/ZrC–SiC composites without and with a thin PyC interlayer of 0.15 µm possess much poor flexural strength and fracture toughness. The flexural strength grows with the increase of PyC layer thickness from 0.3 to 1.2 µm. However, the strength starts to decrease with the further increase of the PyC coating thickness to 2.2 µm. The highest flexural strength of 272.3±29.0 MPa and fracture toughness of 10.4±0.7 MPa m^1/2 were achieved for the composites with a 1.2 µm thick PyC coating. Moreover, the use of thicker PyC layer deteriorates the ablation properties of the C_f/ZrC–SiC composites slightly and the ZrO₂ scale acts as an anti-ablation component during the testing.     

Preparation and mechanical properties of the 2.5D ASf/ZrO2 composites after high-temperature heat treatment

In the paper, the aluminosilicate fiber-reinforced zirconia (AS_f/ZrO₂) ceramic composites were successfully fabricated by polymer impregnation and pyrolysis (PIP) method. The microstructure and high-temperature mechanical properties of the original composites were well studied. The results revealed that the composites could maintain the stability of microstructure at 1000 °C. The flexural strength increased from 58.82 ± 2.83 MPa to 88.74 ± 6.20 MPa and the flexural modulus increased from 29.26 ± 4.67 GPa to 40.76 ± 8.76 GPa. The thermal exposure improved the interfacial bonding and made the load transfer more effective. After heat treatment from 1200 °C to 1400 °C, the flexural strength gradually declined due to the crystallization of the AS fibers and ZrO₂ matrix, while the flexural modulus increased in a completely different trend. After heat treatment at 1400 °C, the composites could maintain a flexural strength of 66.95 ± 4.24 MPa with a flexural modulus of 60.42 ± 7.25 GPa. But the fracture mode gradually evolved to brittleness.     

Fabrication of 2D C/C-SiC composites using PIP based hybrid process and investigation of mechanical properties degradation under cyclic heating

2D C/C-SiC composites were fabricated using PIP process by repeated impregnations of porous C/C composite preforms with polycarbosilane followed by pyrolysis. Effect of cyclic heating on flexural and shear strength of these composites was studied by exposing the test specimens to oxyacetylene flame for 20 s and cooling by a blast of air. The cyclic heating tests were repeated up to five times. Average flexural and shear strength of the as fabricated composites were about 330 MPa and 14.5 MPa respectively. After five heating and cooling cycles, average flexural and shear strength were reduced to 120 MPa and 5.5 MPa respectively. SEM, XRD, EDAX and XPS studies were also carried out to investigate the causes of strength reduction. Oxidation started preferentially at carbon matrix through the cut ends of the weft fibers. Oxidative damage due to repeatedly heating cooling was found to be much smaller in through-thickness direction due to passive oxidation of SiC matrix while severe damage was observed parallel to the fabric layers.     

Mechanical and electromagnetic shielding properties of carbon fiber reinforced silicon carbide matrix composites

Carbon fiber reinforced SiC matrix composites (C_f/SiC) were fabricated through chemical vapor infiltration. Effects of SiC content on the mechanical and electromagnetic properties of the as-prepared materials were studied systematically. The high volume fraction of SiC matrix is beneficial to the transfer of load to carbon fiber. With the increase of SiC content from 21.5 to 42.2 vol.%, the total porosity decreases from 38.5 to 17.8 vol.%, the flexural strength and fracture toughness of C_f/SiC increase from 38 ± 4 to 375 ± 10 MPa and from 6.2 ± 0.7 to 21 ± 0.3 MPa m^1/2. The electromagnetic interference shielding effectiveness of as-prepared C_f/SiC decreases from 43 ± 1.4 to 31 ± 1.1 dB over the frequency range of 8.2–12.4 GHz with the increase of SiC content. The decease of electromagnetic interference shielding effectiveness is mainly attributed to the decline of absorption loss. With the increase of SiC content, the electrical conductivity of C_f/SiC diminishes, leading to the conspicuous drop of the conductive loss, which plays the key role in lowering the absorption loss of electromagnetic waves.     

Effects of post-sintering annealing on the microstructure and toughness of hot-pressed SiCf/SiC composites with Al2O3-Y2O3 additions

This study examined the effects of post-sintering heat treatment on enhancing the toughness of SiC_f/SiC composites. Commercially available Tyranno^® SiC fabrics with contiguous dual ‘PyC (inner)-SiC (outer)’ coatings deposited on the SiC fibers were infiltrated with a SiC + 10 wt% Al₂O₃-Y₂O₃ slurry by electrophoretic deposition. SiC green tapes were stacked between the slurry-infiltrated fabrics to control the matrix volume fraction. Densification of approximately 94% ρ_theo was achieved by hot pressing at 1750 °C, 20 MPa for 2 h in an Ar atmosphere. Sintered composites were then subjected to isothermal annealing treatment at 1100, 1250, 1350, and 1750 °C for 5 h in Ar. The correlation between the flexural behavior and microstructure was explained in terms of the in situ-toughened matrix, phase evolution in the sintering additive, role of dual interphases and observed fracture mechanisms. Extensive fractography analysis revealed interfacial debonding at the hybrid interfaces and matrix cracking as the key fracture modes, which were responsible for the toughening behavior in the annealed SiC_f/SiC composites.     

Mechanical and dielectric properties of SiCf/SiC composites fabricated by PIP combined with CIP process

2D KD-1 SiC fiber fabrics were employed to fabricate SiC_f/SiC composites by an improved polymer infiltration and pyrolysis (PIP) process, combined with cold isostatic pressing (CIP). The effect of CIP process on the microstructure, mechanical and dielectric properties of SiC_f/SiC composites was investigated. The infiltration efficiency was remarkably improved with the introduction of CIP process. Compared to vacuum infiltration, the CIP process can effectively increase the infiltrated precursor content and decrease the porosity resulting in a dense matrix. Thus SiC_f/SiC composites with high density of 2.11 g cm⁻³ and low porosity of 11.3% were obtained at 100 MPa CIP pressure, together with an increase of the flexural strength of the composites from 89 MPa to 213 MPa. Real part (ε′) and the imaginary part (ε″) of complex permittivity of SiC_f/SiC composites increase and vary from 11.7-i9.7 to 15.0-i12.8 when the CIP pressure reaches 100 MPa.     

Effect of short carbon fiber content on the mechanical properties of TiB2-based composites prepared by spark plasma sintering

In this study, TiB₂-30 vol% SiC composites containing 0, 5, 10, and 15 vol% short carbon fibers (C_f) were produced by spark plasma sintering (SPS). The effect of carbon fiber content on microstructure, density, and mechanical properties (micro-hardness and flexural strength) of the fabricated composites was studied. Scanning electron microscopy (SEM) results indicated that the fibers were uniformly dispersed in the TiB₂–SiC matrix using wet ball milling before SPS process. Fully dense TiB₂–SiC–C_f composites were achieved by SPS process at 1900°C for 10 min under 30 MPa. With the addition of fibers, the relative density of the composites did not change considerably. Mechanical tests revealed that microhardness was reduced about 19% by the incorporation of carbon fibers, whereas the flexural strength improved significantly. However, the flexural strength diminished by adding carbon fibers above to critical value (5 vol%) due to residual thermal stresses, nonhomogeneous structure and graphitization of carbon fibers. It was found that the composite with 5 vol% C_f had the highest flexural strength (482 MPa), which was enhanced by 20% compared with the TiB₂–SiC composite.