The mechanical properties of C/C-ZrC-SiC composites after laser ablation

Considering practical environment, the bending property of C/C-ZrC-SiC, C/C-SiC and C/C composites after ablation was worthily studied. Results revealed that C/C-ZrC-SiC composites had a better laser ablation resistance and higher bending strength retention compared with C/C-SiC and C/C composites. The mass loss rate and ablated depth of C/C-ZrC-SiC composites was − 0.09% and 190.377 μm, respectively. The retention of bending strength of C/C-ZrC-SiC composites was 217.67 ± 44.12 MPa, whose strength decreased by 3.57% compared with that of as-prepared C/C-ZrC-SiC composites. The excellent anti-ablation property and residual bending strength of C/C-ZrC-SiC composites were attributed to the lowest ablative temperature and the effective protection of the ZrO₂ grain and ZrO₂-SiO₂ layer, which were formed by oxidation of ZrC-SiC, evaporation of SiO₂, migration of liquid ZrO₂-SiO₂ and the infiltrated as well as grown ZrO₂. However, the fracture behavior transformation of composites from pseudo-plastic rupture to brittle rupture was induced by the ablation damage.     

Controllable fabrication and mechanical properties of C/C–SiC composites based on an electromagnetic induction heating reactive melt infiltration

To regulate the microstructures of carbide ceramic-doped C/C (C/C-ceramic) composites using reactive melting infiltration (RMI) in a controlled manner, an electromagnetic induction heating RMI (ERMI) was proposed and used to fabricate typical C/C–SiC composites herein. Because the tedious heating and cooling regions could be bypassed using ERMI, excessive graphitization and ceramic overreactions of the ERMI-C/C-SiC composites were effectively avoided, which made the interfacial bonding strength (τ) of the ERMI-C/C–SiC composites (～25.7 MPa) much lower than that of the CRMI-C/C-SiC composites (～36.1 MPa) (fabricated using conventional RMI (CRMI)). A weaker τ value triggered strengthening/toughening mechanisms such as crack deflection, and crack arrest, which ultimately led to higher flexural strength and displacement of the ERMI-C/C–SiC composites than the CRMI-C/C–SiC composites. The proposed ERMI exhibited relatively good controlling capability to regulate the microstructures of C/C-ceramic composites.     

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.     

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.     

The mechanical and repair behavior of damaged carbon/carbon composites

With the aim of understanding the effect of defect types on the mechanical performance of carbon/carbon (C/C) composites, three kinds of defects such as circle arc, square, and triangle shapes were prefabricated on their surfaces. The results show that the prefabricated defects damage the flexural strength of C/C composites compared to the pristine sample (101 ± 6 MPa). The flexural strength of C/C decreased by 30.84%, 45.84%, and 42.58% corresponding to the circle arc, square, and triangle type defects respectively. The defect-repair method with Ni-based solder as the additive was employed to repair the damaged C/C composites. After repair, the stress concentration of C/C composites decreases, and there is a good connection between carbon fiber and the repaired solder so that the load can be transferred continuously, therefore the flexural strength of C/C composites can be improved by 20–28%.     

Fabrication and properties of Cf/ZrC‐SiC‐based composites by an improved reactive melt infiltration

C_f/ZrC‐SiC composites with a density of 2.52 g/cm³ and a porosity of 1.68% were fabricated via reactive melt infiltration (RMI) of Si into nano‐porous C_f/ZrC‐C preforms. The nano‐porous C_f/ZrC‐C preforms were prepared through a colloid process, with a ZrC “protective coating” formed surrounding the carbon fibers. Consequently, highly dense C_f/ZrC‐SiC composites without evident fiber/interphase degradation were obtained. Moreover, abundant needle‐shaped ZrSi₂ grains were formed in the composites. Benefiting from this unique microstructure, flexural strength, and elastic modulus of the composites are as high as 380 MPa and 61 GPa, respectively, which are much higher than C_f/ZrC‐SiC composites prepared by conventional RMI.     

Fabrication and properties of SiCnw-reinforced SiC composites by reactive melt infiltration with BN and PyC interface

To tailor the fiber–matrix interface of SiC nanowires-reinforced SiC (SiC_nw/SiC) ceramic matrix composites (CMCs) for improved mechanical properties, SiC nanowires were coated with BN and pyrolytic carbon (PyC) compound coatings prepared by the dip-coating process in boric acid and urea solution and the pyrolysis of phenolic resin. SiC_nw/SiC CMC with PyC/BN interfaces were fabricated by reactive melt infiltration (RMI) at 1680°C for 1 h. The influences of phenolic resin content on the microstructure and mechanical properties of the CMC were investigated. The results showed that the flexural strength and fracture toughness reach the maximum values of 294 MPa and 4.74 MPa m^1/2 as the phenolic resin content was 16 and 12 wt%, respectively. The displacement–load curve of the sample exhibited a gradient drop with increasing phenolic resin content up to 12 wt%. The results demonstrated that the PyC/BN compound coatings could play the role of protecting the SiC_nw from degradation as well as improving the more moderate interfacial bonding strengths during the RMI.     

Fabrication of C/C-SiC composites using high-char-yield resin

Carbon fiber reinforced ceramic matrix composites (C/C-SiC composites) were fabricated using a type of high-char-yield phenolic resin with the char yield of 81.17 wt.%. Firstly, the fabric prepreg was prepared by spreading the phenolic resin solution onto the two dimensional carbon fiber plain weave fabric and dried consequently. Afterward, the resin was cured and then the carbon fiber reinforced polymer (CFRP) was pyrolyzed to get amorphous carbon. Finally, C/C-SiC composites were obtained through liquid silicon infiltration (LSI) process. SEM micrographs showed that the Si/SiC area was homogeneously dispersed in the matrix, and during the siliconization process, a layer of SiC was formed along the surface of carbon fibers or carbon matrix. The fiber volume of CFRP was about 40 vol.%, which was much lower than other studies. XRD result indicated that only β-SiC type was formed. The result of X-ray computed tomography clearly showed the structure changes before and after the melt infiltration process. Mechanical property test showed that the composites had fracture strength of 186 ± 23 MPa, and a flexural modulus of 106 ± 8 GPa.     

Microstructure and ablation behaviors of a novel gradient C/C-ZrC-SiC composite fabricated by an improved reactive melt infiltration

An improved reactive melt infiltration (RMI) route using Zr, Si tablet as infiltrant was developed in order to obtain high-performance and low-cost C/C-ZrC-SiC composite with well defined structure. Two other RMI routes using Zr, Si mixed powders and alloy were also performed for comparison. Effects of different infiltration routes on the microstructure and ablation behavior were investigated. Results showed that C/C-ZrC-SiC composite prepared by Zr, Si tablets developed a dense gradient microstructure that content of ZrC ceramic increased gradually along the infiltration direction, while that of SiC ceramic decreased. Composites prepared by Zr, Si mixed powders and alloy showed a homogeneous microstructure containing more SiC ceramic. In addition, two interface patterns were observed at the carbon/ceramic interfaces: continuous SiC layer and ZrC, SiC mixed layers. It should be due to the arising of stable Si molten pool in the tablet. Among all as-prepared samples, after exposing to the oxyacetylene flame for 60 s at 2500 °C, C/C-ZrC-SiC composite infiltrated by Zr, Si tablet exhibited the best ablation property owing to its unique gradient structure.     

Ablation properties of C/C-UHTCs and their preparation by reactive infiltration of K2MeF6 (Me = Zr,Ti) molten salt

Ultra-high temperature ceramic-modified C/C composites (C/C-UHTCs) were prepared by the reactive infiltration of K₂MeF₆ (Me = Zr, Ti) mixed with Si and Zr-Si powders. Molten salt infiltration can be divided into two stages: salt ion melt and Me-Si alloy melt. In the temperature range below 1400 °C, Zr and Si dissolve in the molten salt, are carried by the ion melt, and precipitate at the PyC interface to form carbides. Above 1400 °C, a large amount of molten salt volatilises and thermally decomposes. The Me-Si alloy forms a melt and infiltrates the C/C matrix, and finally forms C/C-ZrC-SiC, C/C-Ti₃SiC₂-SiC, and C/C-ZrC-TiC-SiC composites. The C/C-ZrC-SiC composite with the highest ZrC content exhibited the lowest mass rate (2.6 ± 0.02 mg/s) and linear ablation rate (0.82 ± 0.04 μm/s), which were reduced by 43.5 and 50.8 %, respectively, compared to the unmodified C/C-ZrC-SiC composite.     

Influence of graphitization temperature on microstructure and mechanical property of C/C-SiC composites with highly textured pyrolytic carbon

C/C-SiC composites with highly textured pyrolytic carbon (HT PyC) were prepared by a combining chemical vapor infiltration and liquid silicon infiltration. The effect of HT PyC graphitization before and after 2327 and 2723 K on C/C-SiC composites was investigated. The mechanical properties decreased with increasing graphitization temperature, but graphitization treatment changed the fracture behavior from brittle like to pseudo-ductile. The decrease in bending strength from 306.21 to 243.69 MPa resulted from the weak interfacial bonding between HT PyC and fiber, and the good orientation of graphite layers. The crack at border of fiber bundle and longitudinal crack in HT PyC shortened the path of crack propagation, resulting in fracture toughness decrease from 21.11 to 14.72 MPa·m^1/2. A more pseudo-ductile behavior was due to the longer pull-out of fibers, the better orientation of graphite layers, the sliding of sublayers, and the deflection and propagation caused by the transverse cracks.     

Fabrication and optimization of 3D-Cf/HfC-SiC-based composites via sol-gel processing and reactive melt infiltration

In this work, 3D-C_f/HfC-SiC-based composites were fabricated and optimized via reactive melt infiltration (RMI) of Si into porous C_f/HfC-C preforms prepared by a sol-gel processing. The physical and chemical processes involved during the fabrication were identified and analyzed in details. It is revealed that fibers and interphase of the composites can be eroded during carbothermal reduction process, which can be further aggravated during RMI, with the formation of Hf-containing substance on the fibers surface. The fibers and interphase degradation is mainly induced by the reactions between HfO₂ and C/SiC interphase layers at elevated temperatures. Accordingly, a two-step carbothermal reduction treatment was proposed for the optimization of the fabrication procedure. As a result, less fiber/interphase erosion and improved mechanical properties are achieved in the composites, with the bending strength increased by ～49 % (from 214.1 ± 15.7 MPa to 319.0 ± 26.0 MPa).     

Fabrication of C/SiC composites by siliconizing carbon fiber reinforced nanoporous carbon matrix preforms and their properties

Reactive melt infiltration (RMI) has been proved to be one of the most promising technologies for fabrication of C/SiC composites because of its low cost and short processing cycle. However, the poor mechanical and anti-ablation properties of the RMI-C/SiC composites severely limit their practical use due to an imperfect siliconization of carbon matrixes with thick walls and micron-sized pores. Here, we report a high-performance RMI-C/SiC composite fabricated using a carbon fiber reinforced nanoporous carbon (NC) matrix preform composed of overlapping nanoparticles and abundant nanopores. For comparison, the C/C performs with conventional pyrocarbon (PyC) or resin carbon (ReC) matrixes were also used to explore the effect of carbon matrix on the composition and property of the obtained C/SiC composites. The C/SiC derived from C/NC with a high density of 2.50 g cm^?3 has dense and pure SiC matrix and intact carbon fibers due to the complete ceramization of original carbon matrix and the almost full consumption of inspersed silicon. In contrast, the counterparts based on C/PyC or C/ReC with a low density have a little SiC, much residual silicon and carbon, and many corroded fibers. As a result, the C/SiC from C/NC shows the highest flexural strength of 218.1 MPa and the lowest ablation rate of 0.168 µm s^?1 in an oxyacetylene flame of ～ 2200 °C with a duration time of 500 s. This work opens up a new way for the development of high-performance ceramic matrix composites by siliconizing the C/C preforms with nanoporous carbon matrix.     

The effect of heat treatment on tensile properties of 2D C/SiC composites

Two-dimensional (2D) carbon fiber reinforced silicon carbide (C/SiC) composites with different initial strength were prepared by chemical vapor infiltration (CVI). After tensile property testing, results exhibited that as the heat-treatment temperature (HTT) increases to 1900°C, the tensile strength and toughness of the low strength specimen (LSS) increased by 110% and 530%, while the high strength specimen (HSS) increased by 5.4% and 550%, respectively. As observed from morphologies, the heat treatment increases the graphitization of the amorphous PyC interphase, which leads to the weakening of interfacial bonding strength (IBS). Meanwhile, the defects arising from heat treatment cause thermal residual stress relaxation. Therefore, the tensile strength and toughness of LSS with relatively high initial IBS increase significantly as HTT increases. For HSS with moderate initial IBS, the heat treatment slightly improves the tensile strength, but significantly improves the toughness. Consequently, the post-heat-treatment tensile properties of 2D C/SiC composites can be regulated by varying HTTs and different initial strength.     

Microstructure and mechanical performance evolution of C/C–ZrC composites exposed to oxyacetylene flame

C/C–ZrC composites were prepared by isothermal chemical vapor infiltration (ICVI) combined with reactive melt infiltration (RMI). The ablation behavior of the C/C–ZrC was investigated using an oxyacetylene flame. The effect of ablation time on the microstructure and mechanical property evolution of the composite was studied. The results showed that as the ablation time prolonged, the linear and mass ablation rates of the composite increased firstly and then stabilized. After 15 s ablation, the flexural strength and modulus of the C/C–ZrC were interestingly increased by 141.8% and 40.9%, which reached 138.42 MPa and 6.45 GPa, respectively. During ablation, the preferential oxidation effect of ZrC could mitigate the oxidation of pyrolytic carbon (PyC) and carbon fibers, and the volume change induced by the ZrC →ZrO₂ phase transformation could weaken its bonding with PyC, which was beneficial for releasing the internal residual stresses of the C/C–ZrC and then contributed to the mechanical performance improvement.     

Preparation and properties of SiC/SiC-SiYC with excellent water-oxygen corrosion resistance

In this study, the SiC/SiC-SiYC composites were fabricated via chemical vapor infiltration (CVI) combined with the reactive melt infiltration (RMI) process. The excellent infiltration of Si-Y alloy assisted in fabricating composites with a density of 2.94 g/cm³ and a porosity of only 2.0%. After 20 h of corrosion at 1300 °C in the water-oxygen environment, the generated oxide layer, consisting of a glass layer and a diffusion layer, effectively protected the composites, and the flexural strength retention is 114.2%. This study highlights the significant potential of Si-Y alloy as a modification phase that is resistant to water and oxygen. It also presents a novel approach for developing high-density ceramic matrix composites that are resistant to water-oxygen corrosion.     

Adhesion Improvement of Bio-Based Epoxy in Environmentally Friendly and High-Performance Natural Fiber-Reinforced Composites

Developing robust bio-based epoxy against petroleum-derived epoxy is necessary for environmentally friendly and high-performance natural fiber-reinforced composites. A bio-based vanillin epoxy (VE) is synthesized from the lignin-derived vanillin, and a thermoset resin is prepared after mixing it with a 4,4′-diaminodiphenyl methane (DDM) hardener. Further, it is infused in high-cellulose-containing alkali-treated jute fiber (TJF) mats through a simple approach to enhance the adhesion between the VE-DDM and TJF. Bio-based VE-DDM resin shows better compatibility with TJF than petroleum-derived bisphenol A diglycidyl ether (DGEBA) epoxy. The bio-based VE-DDM/TJF composite demonstrates the T_gis ≈165 °C, tensile strength is ≈83.12 ± 3.80 MPa, and Young's modulus is ≈2.86 ± 0.10 GPa with excellent flexural strength (138.72 ± 3.81 MPa) and flexural modulus (8.01 ± 0.11 GPa). It also shows merits regarding hydrophobicity, reduced water absorption ability, durability, and chemical resistance in an acidic medium. The natural fiber-reinforced VE composites pave the way to produce environmentally friendly and high-performance composites for structural applications.     

Fabrication and characterization of PIP based C/SiC composites having improved mechanical properties using high modulus M40J carbon fiber as reinforcement

PIP based C/SiC composites are fabricated using high modulus M40J carbon fiber. High ceramic yield polycarbosilane (PCS) was also synthesized in the laboratory and the same was used to infiltrate the fibrous preforms. The infiltrated preforms were pyrolyzed at three different temperatures viz. 1400, 1500 and 1600 °C and termed as set-1, set-2 and set-3. Flexural strength was determined using 3-point bend fixture and the data obtained are analyzed using Weibull distribution. Average flexural strengths were found to be 691±23 MPa, 654.6±24 MPa, and 504±31 MPa for the sets 1, 2 and 3 respectively and the corresponding Weibull moduli were found to be 27.9, 25.5 and 15.6. The composites pyrolyzed at 1400 and 1500 °C, have been found to exhibit extensive fiber pull-out and thus demonstrated pseudo-ductile fracture behavior. A relatively brittle fracture was observed for the composites pyrolyzed at 1600 °C. Area under the flexural stress and displacement curve is found to be in the ratio 1.0:0.92:0.8 for the for the sets 1, 2 and 3 respectively. The effect of the pyrolysis temperature on the mechanical properties is discussed in the light of the microstructure of the composites.     

Microstructure and flexural strength of C/HfC-ZrC-SiC composites prepared by reactive melt infiltration method

C/HfC-ZrC-SiC composites were fabricated via reactive melt infiltration (RMI) of the mixed HfSi₂ and ZrSi₂ alloys. The microstructure, infiltration behavior of the hybrid silicide alloys infiltrating C/C composites, and flexural strength of C/HfC-ZrC-SiC composites was studied. Inside composites, there were more Hf-rich (Hf, Zr)C phases distributed in the exterior region, while more SiC and Zr-rich (Zr, Hf)Si₂ in the interior region. There was compositional segregation in (Hf, Zr)C, with the HfC content decreasing from the exterior region to interior region. The RMI process was performed at different temperatures to investigate the structural evolution, and a model for the reactive melt infiltration of the mixed HfSi₂ and ZrSi₂ alloys into C/C composites was established. Compared with C/HfC-SiC and C/ZrC-SiC prepared by same process, C/HfC-ZrC-SiC had the highest flexural strength of 247Mpa and 213Mpa after oxidation at 1200 ℃ for 15 min. Both the unoxidized and oxidized samples presented a pseudo-plastic fracture behavior.     

Preparation of SiC/SiC composites with high toughness by reaction of the SiCP+C double-cladding layer with liquid silicon

SiC/SiC composites prepared by liquid silicon infiltration (LSI) have the advantages of high densification, matrix cracking stress and ultimate tensile strength, but the toughness is usually insufficient. Relieving the residual microstress in fiber and interphase, dissipating crack propagation energy, and improving the crystallization degree of interphase can effectively increase the toughness of the composites. In this work, a special SiC particles and C (SiC_P +C) double-cladding layer is designed and prepared via the infiltration of SiC_P slurry and chemical vapor infiltration (CVI) of C in the porous SiC/SiC composites prepared by CVI. After LSI, the SiC generated by the reaction of C with molten Si combines with the SiC_P to form a layered structure matrix, which can effectually relieve residual microstress in fiber and interphase and dissipate crack propagation energy. The crystallization degree of BN interphase is increased under the effects of C-Si reaction exotherm. The as-received SiC/SiC composites possess a density of 2.64 g/cm³ and a porosity of 6.1%. The flexural strength of the SiC/SiC composites with layered structure matrix and highly crystalline BN interphase is 577 MPa, and the fracture toughness reaches up to 37 MPa·m^1/2. The microstructure and properties of four groups of SiC/SiC composites prepared by different processes are also investigated and compared to demonstrate the effectiveness of the SiC_P +C double-cladding layer design, which offers a strategy for developing the SiC/SiC composites with high performance.