PyC Interface Research Articles

Fracture mechanical and ablation behaviors of C/SiC–Cu3Si–Cu interpenetrating composites and their dependence on metal addition and interface thickness

The C/SiC–Cu3Si–Cu interpenetrating composites were prepared by the ceramization and metallization of carbon fiber reinforced carbon aerogel (C/CA) preforms. Fracture mechanical and ablation behaviors as well as their dependence on metal addition and PyC interface thickness were investigated. With the presence of metallic components, the C/SiC–Cu3Si–Cu composites show pseudo-plastic fracture, typical brittle-plastic mixed fracture, and then ladder-like fracture with the PyC interface thickness increasing due to the co-existence of ductile and brittle components, obviously different from the fracture of conventional ceramic matrix composites. The composite with 3.0 μm-thick interface has the highest flexural strength of 292.8 MPa due to the proper interfacial bond strength and residual compressive stress. The composite with 1.9 μm-thick interface has the highest work of fracture but relatively low fracture toughness due to the abundant modes of crack propagation. The anti-ablation property is deteriorated with increased PyC thickness due to the weakened transpiration cooling effect and reduced oxide scale quality. The composite with 0.9 μm-thick interface exhibits lower mass and linear ablation rates of 0.054 mg cm−2 s−1 and 0.018 μm s−1 after ablation at 2200 °C for 600 s, respectively. This work provides vital insights into the control of the overall performance of carbon fiber reinforced ceramic-metal matrix composites.

Preparation and mechanical properties of Cf/SiC composites via pressure-assisted gel impregnation and PIP

Non-uniform shrinkage of SiC precursors will lead to cracking and thus weaken the mechanical properties of the Cf/SiC composites. This study used the pressure-assisted gel impregnation method to introduce SiC particles (SiCp) into the carbon fiber preform and combined the PIP technique to fabricate Cf/SiC composites. The mechanism of enhancing the mechanical properties of composites was studied. Results showed that SiCp effectively eliminated matrix cracking, and the PyC interface layer inhibited interfacial crack propagation. The combined effect of the two resulted in a significant improvement in the mechanical properties of the composites. Specifically, the maximum flexural strength of the Cf/SiC composites was 360.63±26.02 MPa, and the maximum fracture toughness was 8.57±1.82 MPa·m1/2.

Oxygen permeation mass transfer modeling and onion-like micromechanical modeling to predict the effect of multilayered interface on oxidation resistance and mechanical properties of composites

To predict oxidative damage of interfaces and fibers under high temperature aerobic environment and mechanical strength of composites before and after oxidation, oxygen permeation mass transfer modeling and onion-like micromechanical modeling of multilayered interface were proposed. The oxygen mass transfer theory and oxidation damage theory of PyC interface were used to establish the two models. The oxidative damage of PyC interface was extended to (PyC-SiC)n multilayered interface, and transformation of SiC phase and microcracks caused by thermal mismatch were also considered. The law of oxygen permeation mass transfer and the evolution of fiber oxidative damage in the “Carbon fiber/(PyC-SiC)n multilayered interface” region were revealed. The mechanical strength of composites under different interface layers was researched, resembling an onion-like wrapping in layers from the core outwards. Furthermore, Cf@(PyC-SiC)n/SiC(n = 1/2/3/4) composites were prepared by chemical vapor infiltration (CVI) method. The mechanical properties of the composites were tested before and after oxidation. A comparison was made between the experimental and predicted tensile strengths before and after oxidation. The predicted results of tensile strength were found to be in good agreement with the experimental ones. In addition, the results show that PyC-SiC multilayered interface has a positive effect on the tensile strength of the composites, mainly as the cracks are deflected and branched by the multilayered interface to promote the multistage pull-out of the fibers. With the increase of interface number, the oxygen diffusion path was lengthened and zigzagged, reducing the oxidative damage of fiber and interface.

Ablation behavior of 3D PyC-Cf/SiHfBOC Composites under an oxyacetylene torch environment above 2000 °C

A high-pressure assisted precursor impregnation pyrolysis method (PIP) was used to prepare 3D PyC-Cf/SiHfBOC composites. Its anti-ablation properties were tested in an oxygen-acetylene torch ablation environment exceeding 2000 °C. They revealed the ablation behavior and mechanism of SiHfBOC ceramics, carbon fiber, and the PyC interface layer. Under the action of Hf modification, a dense HfO2-SiO2 oxide layer was formed in situ on the surface of 3D PyC Cf/SiHfBOC composites, effectively preventing further ablation of the composite's matrix by high-temperature oxidation gases. During the ablation process of an oxyacetylene torch at 2000 °C, it still exhibits excellent anti-ablation properties (linear ablation rate of 1.10 × 10−4 mm s−1). This work enriches the system of hafnium containing ultra-high temperature ceramic precursors and their composites, which provides beneficial exploration for their application in the ultra-high temperature field.

Obtaining SiC Fibers–PyC interfacial properties through push-out FEM Models

Silicon carbide (SiC) has attractive properties for use in nuclear reactors. However, it is hampered by inherent brittleness that is overcome through a fiber-reinforced composite. A finite element model based on cohesive zone contact coupled to Coulomb friction is proposed to simulate the push-out response of isolated fibers in SiC/PyC fiber-reinforced composites. The model reproduces the measurements obtained during push-out experiments of isolated fibers in different configurations and predicts interfacial failure between the PyC interphase and fiber. The brittle properties predicted coincide with literature indicating that fiber–PyC interface could prevent the crack propagation through the fiber, fulfilling the function of the structure.

The dynamic thermophysical properties evolution and multi-scale heat transport mechanisms of 2.5D C/SiC composite under high-temperature air oxidation environment

The variations in thermophysical properties and dynamic heat transfer mechanism of 2.5D C/SiC ceramic matrix composites (2.5D C/SiC-CMC) under a high-temperature air oxidation environment are investigated by experiments and numerical simulations. A new multi-scale thermal analysis model of 2.5D C/SiC-CMC under high-temperature oxidation is proposed to predict its equivalent thermal conductivity and analysis its multi-scale heat transport mechanisms. The multi-scale thermal analysis model is developed by blending the multi-scale asymptotic thermal analysis method and oxidation kinetics theory, which includes the micro-scale model and mesoscale model. The micro-scale model simulates the oxidation process of the carbon fibers and PyC interface through oxidation kinetics, which predicts the varying equivalent thermal conductivity of yarns with oxidation. The mesoscale model is constructed based on the experimental statistics which reflect the multi-scale structure within the 2.5D C/SiC-CMC with oxidation. The mesoscale model introduces oxidation characteristics by considering dynamic variations in yarn thermal properties. The dynamic thermophysical properties of the 2.5D C/SiC-CMC with oxidation are tested in the experimental study, which verifies that the multi-scale thermal analysis model has highlighted prediction accuracy. The results show that high-temperature oxidation causes significant variations in the dynamic thermal behavior of 2.5D C/SiC-CMC which is critical for the practical thermal protection design of 2.5D C/SiC-CMC hot components in engineering applications.

Effect of carbon fiber preform structures on the mechanical properties of Cf@PyC/SiC composites

Cf@PyC/SiC composites, using needle-punched preforms, 3D orthogonal woven preforms and 3D 4-step braided preforms (braiding angles of 10°, 20° and 30°) as the reinforcement, were obtained through chemical vapor infiltration (CVI) method. The tensile strength before and after oxidation of the composites were investigated, and the microstructure, appearance of fracture and phase component of the composites were also analyzed. The results show that the mechanical properties and oxidation resistance of composites are greatly affected by the preform structures. The tensile strengths of 3D 4-step braided composites with the braiding angle of 10° are the best among all composites before and after oxidation, which are 266.40 ± 16.98 MPa and 238.66 ± 14.98 MPa. Before oxidation, the fibers and matrix at the fracture of 3D 4-step braided composites are in staggered distribution. The mechanical enhancement mechanisms of composites such as crack deflection, interface debonding and fiber pull-out, were beneficial to good performance and excellent mechanical properties. After oxidation, the deflection and branching effects of the interface on the crack are not fully manifested, and enhancement and toughening mechanisms are not fully played due to the oxidation of the carbon fiber and the PyC interface.

Effect of carbon interface on adhesion and anti-corrosion properties of hydroxyapatite coating on AZ31 magnesium alloy

In order to improve the adhesion and anti-corrosion properties of hydroxyapatite coating (HA) on the surface of implant magnesium alloy, carbon interface (C) was successfully introduced by resin carbonization method. The adhesion and anti-corrosion properties of the coatings were characterized. After introducing PyC interface, the adhesion of the coating increased by 173%. The corrosion current in the polarization curve decreased by three orders of magnitude, meaning that the corrosion resistance was improved significantly. The microcracks on carbon interface layer surface provided enough bonding strength between the hydroxyapatite coating and carbon coating, due to forming the mortise and tenon embedding structure. The introduction of PyC interface layer improved the overall density of the coating and effectively isolated the contact between the corrosion solution and the magnesium alloy matrix, resulting in that the corrosion resistance was significantly improved.

Influence of heat treatment on microstructure and mechanical properties of Cansas-II SiC/PyC/CVI-SiC mini-composites

The influence of heat treatment at 1300 °C and 1500 °C for 50h on the microstructure and mechanical properties of Cansas-II SiC/PyC/CVI SiC mini-composites was studied in detail. The interfacial shear strength decreases from 98.8 MPa to 13.6 MPa after the heat treatment at 1500 °C for 50h, which was mainly caused by the weak bonding between the SiC matrix and PyC interface due to the decomposition reactions and carbothermic reductions of CVI SiC matrix. The average tensile strength of fibers decreases with the rise of heat treatment temperature, which was primarily attributed to the significant growth of β-SiC grains accompanied by the decomposition of SiC x O y . Due to the protective effect of the PyC interface and CVI SiC matrix on the fibers, the fraction of declined strength of the mini-composites is only 25.8% after the heat treatment at 1500 °C for 50h.

Effect of interface types on the heat-resistance of Cansas-II SiCf /SiC composites

The heat-resistance of the Cansas-II SiC/CVI-SiC mini-composites with a PyC and BN interface was studied in detail. The interfacial shear strength of the SiC/PyC/SiC mini-composites decreased from 15 MPa to 3 MPa after the heat treatment at 1500 °C for 50 h, while that of the SiC/BN/SiC mini-composites decreased from 248 MPa to 1 MPa, which could be mainly attributed to the improvement of the crystallization degree of the interface and the decomposition of the matrix. Aside from the above reasons, the larger declined fraction of the interfacial shear strength of the SiC/BN/SiC mini-composites might also be related to the gaps in the BN interface induced by the volatilization of B 2 O 3 ·SiO 2 phase, leading to a significant larger declined fraction of the tensile strength of the SiC/BN/SiC mini-composites due to the obvious expansion of the critical flaws on the fiber surface. Therefore, compared with the CVI BN interface, the CVI PyC interface has better heat-resistance at high temperatures up to 1500 °C due to the fewer impurities in PyC.

Mechanical property and toughening mechanism of 2.5D C/C-SiC composites with high textured pyrocarbon interface

The application of C/C-SiC composites remains a challenge because of the poor mechanical properties induced by the liquid silicon infiltration method. In this study, a thick high textured pyrolytic carbon (HT PyC) interface manufactured by chemical vapor infiltration (CVI) was used to protect the carbon fibers and improve the flexural properties. The microstructure of HT PyC, its flexural properties, and its associated strengthening and toughening mechanisms were analyzed on the C/C-SiC composites. The results showed that the bending strength of the C/C-SiC composites was 344.74 MPa, which is nearly 31.82% higher than that of C/C composites. The fracture mode transformed from brittle fracture to pseudoplastic fracture owing to the addition of SiC, and the C/C-SiC composites maintained a better toughness compared to C/C composites. Multiple mechanisms of strength and toughness improvement were found to be responsible for the excellent performance of the C/C-SiC composites. The HT PyC interface played a critical role in the excellent flexural properties. The strong bonding among the carbon layers and high interfacial strength between the fiber and HT PyC led to the increase of strength. Besides, the improvement in toughness was attributed to the multiple effects of the carbon-layers deformation, cracks deflection and propagation caused by the bridging areas, sublayers, nano- and micro-scale cracks.

Using PyC modified 3D carbon fiber to reinforce UHTC under low temperature sintering without pressure

Finding the optimum balance between strength and toughness, as well as acquiring reliable thermal shock resistance and oxidation resistance, has always been the most concerned topic in the discussion of ultra-high temperature ceramic composites. Herein, PyC modified 3D carbon fiber is used to reinforce ultra-high temperature ceramic (UHTC). The macroscopic block composite with large size is successfully fabricated through low temperature sintering at 1300 °C without pressure. The prepared PyC modified 3D Cf/ZrC-SiC composites simultaneously possess excellent physical and chemical stability under the synergistic effect of PyC interface layer and low temperature sintering without pressure. The fracture toughness is increased in magnitude to 13.05 ± 1.72 MPa·m1/2 accompanied by reliable flexural strength of 251 ± 27 MPa. After rapid thermal shock spanning from room temperature (RT) to 1200 °C, there are no visible surface penetrating cracks, spalling, or structural fragmentation. The maximum critical temperature difference reaches 875 °C, which is nearly three times higher than that of traditional monolithic ceramics. The haunting puzzle of intrinsic brittleness and low damage tolerance are resolved fundamentally. Under the protection of PyC interface layer, the carbon fibers around oxide layer and matrix remain structure intact after static oxidation at 1500 °C for 30 min. The oxide layer has reliable physical and chemical stability and resists the erosion from fierce oxidizing atmosphere, ensuring the excellent oxidation resistance of the composites. In a sense, the present work provides promising universality in designability and achievement of 3D carbon fiber reinforced ceramic composites.

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.

Study on toughening mechanisms of pyrolytic carbon interface layer in Cf/ZrB2-SiC composites using in-situ tensile experimental and numerical methods

The toughening mechanism in continuous fiber toughened ZrB2-SiC ceramic matrix (Cf/ZrB2-SiC) composites was studied upon introduction of pyrolytic carbon coating at the fiber/matrix interface. The real-time deformation behavior, surface crack initiation and evolution of Cf/ZrB2-SiC composites under tensile load were studied using in-situ scanning electron microscopy (SEM) to determine the typical damage modes and toughening mechanisms. A refined microscopic representative volume element (RVE) inserting the cohesive zone elements was established to study the PyC interface layer damage by using finite element method. It was found that PyC interface layer damage induced by thermal residual stress (TRS) was one of critical factors affecting the mechanical performance of the Cf/ZrB2-SiC composites. The critical thickness of the interface layer was also further determined by analyzing the effect of interface layer thickness on the distribution of TRS, which can guide the design of PyC interface layer for manufacturing the Cf/ZrB2-SiC composites.

Effect of SiC nanowires on the mechanical properties and thermal conductivity of 3D-SiCf/SiC composites prepared via precursor infiltration pyrolysis

In this study, SiC nanowires (SiCNWS) were grown in situ on the surface of PyC interface through chemical vapor infiltration (CVI) to improve the mechanical characteristics and thermal conductivity of three-dimensional SiCf/SiC composites fabricated via precursor infiltration pyrolysis (PIP). The effect of SiCNWS on the properties of the obtained composites was investigated by comparing them with conventional SiCf/PyC/SiC composites. After the deposition of SiCNWS, the flexural strength of the SiCf/SiC composites was found to increase by 46 %, and the thermal conductivity showed an obvious increase at 25−1000 °C. The energy release of the composites in the damage evolution process was analysed by acoustic emission. The results indicated that the damage evolution process was delayed owing to the decrease in porosity, the crack deflection and bridging of the SiCNWS. Furthermore, the excellent thermal conductivity was attributed to the thermally conductive pathways formed by the SiCNWS in the dense structure.

Thermal performance affected by the mesoscopic characteristics of the ceramic matrix composite for hypersonic vehicle

The rigorous thermal environment brought by long-time high-speed flight is imposed severe requirements on the structural bearing capacity and structural thermal safety of the aircraft. The integrated non-ablative thermal protection system based on continuous fiber-reinforced ceramic matrix composites is becoming a hot spot on the design of aircraft structures. However, the multi-scale, non-linear, non-uniform features of such materials, as well as complex thermal and mechanical characteristics, pose serious challenges to structural design and evaluation. Under the aero heating environment, the non-uniform temperature rising and thermal matching between different components in the continuous fiber-reinforced ceramic matrix composites are extremely complicated, which has a significant influence on the thermal safety performance of the structure. In this paper, based on the commonly used 3D orthogonal weaving process and the thermal characteristics prediction method of fiber bundles considering the effect of PyC interface layer, the fluid-structural strong thermal coupling characteristics of different woven parameters in typical aircraft structure is carried out. Quantitatively characterizing the heat transfer characteristics of this new material under the actual flight condition of the aircraft can further to improve the accuracy of the thermal property parameters obtained based on the ground test. The analysis results show that increasing the proportion of fiber bundles in a certain direction is the most effective method to increase the thermal conductivity in this direction. At the same time, the arrangement of the coupling yarns will also have a greatly influence on the thermal conductivity of the material. These results is of great significance for the design of the materials.

Effect of interface types on the static and dynamic mechanical properties of 3D braided SiC/SiC composites after oxidation

For applications in thermal structure engineering, static and dynamic mechanical properties of 3D braided SiC/SiC composites after oxidation were investigated and the effects of interface between fibers and matrix were revealed. The results showed that composites with combined (PyC + SiC) multilayer interface (denoted as K–C/S) were superior to those with a single interlayer or without an interlayer. After oxidation, K–C/S showed the least weight changes, the highest flexure strength, small internal friction, and highest storage modulus. The outside SiC interface of K–C/S protected the PyC interface from further oxidation. Thus, K–C/S showed highly advantageous with regard to both static and dynamic properties after oxidation.

Mechanical properties and strengthening mechanism of SiCf/SiC mini-composites modified by SiC nanowires

The effects of the SiC nanowires (SiCNWs) and PyC interface layers on the mechanical and anti-oxidation properties of SiC fiber (SiCf)/SiC composites were investigated. To achieve this, the PyC layer was coated on the SiCf using a chemical vapour infiltration (CVI) method. Then, SiCNWs were successfully coated on the surface of SiCf/PyC using the electrophoretic deposition method. Finally, a thin PyC layer was coated on the surface of SiCf/PyC/SiCNWs. Three mini-composites, SiCf/PyC/SiC, SiCf/PyC/SiCNWs/SiC, and SiCf/PyC/SiCNWs/PyC/SiC, were fabricated using the typical precursor infiltration and pyrolysis method. The morphologies of the samples were examined using scanning electron microscopy and energy dispersive X-ray spectrometry. Tensile and single-fibre push-out tests were carried out to investigate the mechanical performance and interfacial shear strength of the composites before and after oxidization at 1200 °C. The results revealed that the SiCf/PyC/SiCNWs/SiC composites showed the best mechanical and anti-oxidation performance among all the composites investigated. The strengthening and toughening is mainly achieved by SiCNWs optimization of the interfacial bonding strength of the composite and its own nano-toughening. On the basis of the results, the effects of SiCNWs on the oxidation process and retardation mechanism of the SiCf/SiC mini-composites were investigated.

Effect of PyC interface phase on the cyclic ablation resistance and flexural properties of two-dimensional Cf/HfC composites

Composites based on hafnium carbide and reinforced with continuous naked carbon fiber with and without PyC interface were prepared at low temperature by precursor infiltration and pyrolysis and chemical vapor deposition method. The microstructure, mechanical property, cyclic ablation and fiber bundle push-in tests of the composites were investigated. The results show that after three times ablation cycles, the bending strength of samples without PyC interface decreased by 63.6 %; the bending strength of samples with PyC interface only decreased by 37.8 %. The force displacement curve of the samples with PyC interface presented a well pseudoplastic deformation state. The mechanical behavior difference of two kinds of composites was due to crucial function of PyC interface phase including protection of fiber and weakening of fiber/matrix interface.

Micromechanical properties and microstructural evolution of Amosic-3 SiC/SiC composites irradiated by silicon ions

In this work, Amosic-3 SiC/SiC composites were irradiated to 10 dpa and 115 dpa with 300 keV Si ions at 300 °C. To evaluate its irradiation behaviour and investigate the underlying mechanism, nanoindentation, AFM, Raman and electron microscopy were utilized. Nanoindentation showed that although micromechanical properties declined after irradiation, hardness and Young’s modulus were maintained better under 115 dpa. AFM manifested differential swelling among PyC interface, fiber and matrix and SEM showed irradiation-induced partial interface debonding, which are both more obvious under 115 dpa. TEM revealed the generation and proliferation of amorphous regions, which is according with the decline and broadening of peaks in Raman spectra. The material was almost completely amorphous after irradiated to 10 dpa while recrystallization occurred under 115 dpa. All results mentioned above contribute to the decline of hardness and Young’s modulus and may explain why the micromechanical degradation was more significant under 10 dpa.