Laser ablation resistance and mechanism of Si-Zr alloyed melt infiltrated C/C-SiC composite

Ablation resistance of C/C-SiC composite prepared via Si-Zr alloyed reactive melt infiltration was evaluated using a facile and economical laser ablation method. Linear ablation rates of the composite increased with an increase in laser power densities and decreased with extended ablation time. The C/C-SiC composite prepared via Si-Zr alloyed melt infiltration presented much better ablation resistance compared with the C/SiC composite prepared by polymer infiltration and pyrolysis process. The good ablation resistance of the composite was attributed to the melted ZrC layer formed at the ablation center region. Microstructure and phase composition of different ablated region were investigated by SEM and EDS, and a laser ablation model was finally proposed based on the testing results and microstructure characterization. Laser ablation of the composite experienced three distinct periods. At the very beginning, the laser ablation was dominated by the oxidation process. Then for the second period, the laser ablation was dominated by the evaporation, decomposition and sublimation process. With the further ablation of the composite, chemical stable ZrC was formed on the ablated surface and the laser ablation was synergistically controlled by the scouring away of ZrC melts and evaporation, decomposition and sublimation process.     

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.     

Finite element modeling of reactive liquid silicon infiltration

The LSI process, i.e. the infiltration of molten silicon into porous structures, is one of the most economical techniques for the production of C/C-SiC and C/SiC ceramics. However, despite decades of development, the infiltration behavior affected by phenomena at the infiltration front has not been understood sufficiently. In the present work, a numerical model, based on the finite element method, was developed to simulate the infiltration process. The 3D model includes the penetration of silicon into the porous preform as well as the exothermal reactions at the infiltration front caused by the growth of SiC layers. For model validation, a special measuring furnace was used, enabling in situ optical inspection and weight measurement during liquid silicon infiltration into C/C-preforms in a controlled atmosphere. For the first time, a numerical model could be established which provides a tool to simulate the infiltration kinetics as well as the thermal processes during the LSI process in three dimensions. The model enables the optimization of melt infiltration processes with complex components within reasonable computer times.     

Gel reactive melt infiltration: A new method for large-sized complex-shaped C/C components ceramic modification

To widen the applications of conventional reactive melt infiltration (RMI) in large-sized complex-shaped C/C components, an ingenious process of gel-RMI (GRMI) was proposed in this study. The arching C/CSiC composite was prepared successfully using GRMI method with polycarbosilane (PCS)Si90Zr10 (Si: 90 at.%; Zr:10 at.%) sol. The porosity rate of the C/C preform decreased from 18.5% to 2.9%, while the density was raised from 1.40 g·cm⁻³ to 2.05 g·cm⁻³ after GRMI. The reason why C/C preform has been significantly densified is as follow: the PCS in PCS-Si90Zr10 sol formed SiC aerogel skeleton after pyrolysis, and then the Si90Zr10 powders were melted and released from the SiC aerogel into the C/C preform body when the temperature reached the melting point of Si90Zr10 alloy. The obtained C/CSiC composite showed a pseudo-ductile rupture characteristic distinguished from that of the C/C preform, and its bending strength was significantly improved from 104.2 MPa of the C/C preform to 258.8 MPa. The C/CSiC composite had a far lower mass ablation rate of 0.75 mg·s⁻¹ than that of C/C preform, 23.30 mg·s⁻¹. Moreover, the GRMI was preliminarily applied in ceramic modifying nozzle-like C/C preform, and the result showed that the nozzle-like C/C preform was successfully densified from 1.3 g cm⁻³ to 1.96 g cm⁻³. The GRMI process has great potential in ceramic modifying large-sized complex-shaped C/C components.     

Reactive alloy melt infiltration for SiC composite matrices: Mechanistic insights

A comparative study of reactive melt infiltration using Si and Si‐Y alloys is presented to provide insight into the governing processes that control the effectiveness of the melt interaction with a carbonaceous preform and the temperature capability of the SiC matrix for ceramic matrix composites. Through experiments on two substantially different scales of capillaries in porous graphite tubes using Si and Si‐Y alloys, the current study has characterized the phenomena that play a role in the infiltration of the melt and its reaction with the preform. It is shown that (i) the interface reaction controls wetting in both large and small capillaries and the climb rate is enhanced by the presence of Y; (ii) reaction choking occurs at critical throats within the pore network, usually behind the infiltration front; and (iii) different residual silicides can form during reaction and upon cooling. A potential mechanism for SiC growth is described, and the implications for the interplay between SiC growth and infiltration are discussed.     

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.     

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

Abstract

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

Influence of graphitization treatment on microstructure and flexural strength of C/C-ZrC-SiC composites fabricated via reactive melt infiltration

C/C-ZrC-SiC composites were prepared by chemical vapor infiltration (CVI) and molten salt assisted reactive melt infiltration (RMI). The microstructure of low density and high density C/C composites without graphitization (LC/HC) and graphitization at 2000 °C (LCG/HCG) were compared. Moreover, the effects of graphitization of LC and HC on the microstructure and flexural strength of C/C-ZrC-SiC composites were investigated in detail. The composites prepared by infiltration of LC and LCG had lower flexural strength, 220.01 ± 21.18 MPa and 197.94 ± 19.05 MPa, respectively. However, the composites prepared by HC and HCG presented higher flexural strength, 308.76 ± 12.35 MPa and 289.62 ± 8.70 MPa, respectively. This was due to the phenomenon of fiber erosion in both LC and LCG during the RMI process. After graphitization, the flexural strength of C/C-ZrC-SiC composites prepared by RMI decreased, but the fracture behavior of the composites tends to be more mild. The decreased strength of the composites were caused by the increased matrix cracks, fiber damage in high temperature and the weak interfacial bonding. The improve of failure behavior of the composites was due to interface debonding between the fiber and matrix, and composites can consume the fracture energy through fiber pull-out.     

Strength evolution of cyclic loaded LSI-based C/C-SiC composites

An experimental investigation was performed to study the influence of fatigue damage introduced by different loading cycles on the residual tensile strength (RTS) of plain-weave reinforced C_f/C-SiC composites (2D C/C-SiC). The specimens were subjected to the fatigue stress of 57 MPa for the preselected numbers of cycles as follows: 10², 10⁴ and 10⁵, respectively, before the static tensile test. The microstructures and fractured surfaces after the tensile test were examined by optical and scanning electron microscopy, respectively. The results showed that the RTS of the specimens after the preselected fatigue cycles numbers of 10², 10⁴ and 10⁵ increase to 89.8, 94.1 and 82.4 MPa, respectively, which are somewhat higher compared to the virgin samples (79.7 MPa). Additionally, we found that the linear part of the tensile stress-strain curve is independent on the fatigue cycles. Finally, the increased fatigue damage in C/C-SiC composites could determine a reduction of elastic modulus in all cases of fatigue tests.     

Comparative ablation behaviors of C/SiC-HfC composites prepared by reactive melt infiltration and precursor infiltration and pyrolysis routes

Carbon fiber reinforced silicon carbide-hafnium carbide (C/SiC-HfC) composites were prepared by reactive melt infiltration (RMI) and precursor infiltration and pyrolysis (PIP) routes. The ablation behaviors of the two composites were investigated and compared under an oxyacetylene torch flame. The C/SiC-HfC composites prepared by PIP showed a better ablation resistance than those synthetized by RMI. Microstructural observations revealed an island distribution of HfC for the sample prepared by RMI, which resulted in SiC being directly oxidized during the ablation process. In contrast, the PIP-prepared sample showed a uniform distribution of HfC, which resulted in SiC being oxidized via the Knudsen diffusion mechanism under ablation. The Knudsen diffusion of oxidants retarded the oxidation process, thereby increasing the ablation resistance of the C/SiC-HfC composites prepared by PIP.     

Effects of preform pore structure on infiltration kinetics and microstructure evolution of RMI-derived Cf/ZrC-ZrB2-SiC composite

Reactive melt infiltration (RMI) is often used to fabricate highly dense ceramic matrix composite by infiltration of alloy melt into porous preform. Here, C_f/B₄C-C preforms with various pore structures were prepared, and the effects of pore structure on the ZrSi₂ melt infiltration and the as-received C_f/ZrC-ZrB₂-SiC composites were investigated. Compared with the preform prepared by slurry impregnation (SI), the preform prepared by sol impregnation shows more uniform pore size distribution, which leads to more homogeneous melt infiltration, as well as more uniform formation of ZrC-ZrB₂-SiC and better mechanical properties in the composites. The calculation results of infiltration kinetics indicate that the pore radius decreases quickly during the melt infiltration. As the time needed for pore closure in sol-preform is longer than that in SI-preform, it makes the infiltration kinetics more favorable in the former preform. This study can provide guidance for the pore structure regulation in the fabrication of RMI-composites.     

Effect of TiO2 addition on the properties of Ti3Si(Al)C2 based ceramics fabricated by reactive melt infiltration

In this paper, Ti₃Si(Al)C₂ based ceramics were fabricated by reactive melt infiltration (RMI) of TiC/TiO₂ preforms with liquid silicon. The microstructure, phase composition, and mechanical properties of the Ti₃Si(Al)C₂ based ceramics have been investigated to understand the effect of phase composition of the preforms on the formation mechanisms of Ti₃Si(Al)C₂. The preforms with different content of TiO₂ infiltrated at 1500 °C with liquid silicon for 1 h were composed of Ti₃Si(Al)C₂, Al₂O₃, TiC, TiSi_xAl_y and residual Al. The prior generated Al₂O₃ phases inhibited the dispersion of Ti₃Si(Al)C₂ phases, resulting in the drastically grain growth of Ti₃Si(Al)C₂. Subsequently, the microstructure with gradually increasing Ti₃Si(Al)C₂ grain size resulted in the decrease of the bending strength and fracture toughness of samples. When the content of TiO₂ reached 20 wt%, the bending strength reached the maximum, 326.6 MPa. The fracture toughness attained the maximum, 4.3 MPa m^1/2, when the content of TiO₂ was 10 wt%.     

Characterization and modeling of tensile properties of continuous fiber reinforced C/C-SiC composite at high temperatures

In order to study the effects of temperature on the material behavior of Liquid Silicon Infiltration (LSI) based continuous carbon fiber reinforced silicon carbide (C/C-SiC), the mechanical properties at room temperature (RT) in in-plane and out-of-plane directions are summarized and the tensile properties of C/C-SiC were then determined at high temperature (HT) 1200 °C and 1400 °C under quasi static and compliance loading. The stress-strain response of both HT tests is similar and almost no permanent strain can be observed compared to the RT, which can be explained through the relaxation of residual thermal stresses and the crack distribution under various states. The different fracture mechanisms are confirmed by the analysis of fracture surface. Furthermore, based on the analysis of hysteresis measurements at RT, a modeling approach for the prediction of material behavior at HT has been developed and a good agreement between test and modeling results can be observed.     

The ablation behavior and mechanical property of C/C-SiC-ZrB2 composites fabricated by reactive melt infiltration

In order to improve the ablation resistance of carbon/carbon (C/C) composites, SiC-ZrB₂ di-phase ceramic were introduced by reactive melt infiltration. The ablation properties of these composites were evaluated by oxyacetylene torch with a heat flux of 2.38 MW/m² for 60 s. Compared with the pure C/C composites, the C/C-SiC-ZrB₂ composites show a significant improvement in the ablation resistance, and the linear and mass ablation rates decreased from 10.28×10⁻³ mm/s to 6.72×10⁻³ mm/s and from 3.08×10⁻³ g/s to 0.61×10⁻³ g/s, respectively. After ablation test, the flexural strength retentions of the C/C and C/C-SiC-ZrB₂ composites near the ablated center region are 39.7% and 81.6%, respectively. The higher strength retention rate of C/C-SiC-ZrB₂ composites was attributed to the introduction of SiC-ZrB₂ ceramic phases, which have excellent ablation resistant property. During ablation test, an ‘embedding structure’ of Zr-O-Si glass layer was formed, which could act as an effective barrier for oxygen and heat. The oxide ceramic coating could protect the C/C-SiC-ZrB₂ composites from further ablation, and thus contribute to retaining the mechanical property of C/C-SiC-ZrB₂ composites after ablation.     

Reactive infiltration processing (RIP) of ultra high temperature ceramics (UHTC) into porous C/C composite tubes

A novel reactive infiltration processing (RIP) technique was employed to infiltrate porous carbon fibre reinforced carbon (C/C) composite hollow tubes with ultra high temperature ceramic (UHTC) particles such as ZrB₂. The C/C composite tubes had initial porosity of ∼60% with a bimodal (10 μm and 100 μm) pore size distribution. A slurry with 40-50% ZrB₂ solid loading particles was used to infiltrate the C/C tubes. Our approach combines in situ ZrB₂ formation with coating of fine ZrB₂ particles on carbon fibre surfaces by a reactive processing method. A Zr and B containing diphasic gel was first prepared using inorganic-organic hybrid precursors of zirconium oxychloride (ZrOCl₂·8H₂O), boric acid, and phenolic resin as sources of zirconia, boron oxide, and carbon, respectively. Then commercially available ZrB₂ powder was added to this diphasic gel and milled for 6 h. The resultant hybrid slurry was vacuum infiltrated into the porous hollow C/C tubes. The infiltrated tubes were dried and fired for 3 h at 1400 °C in flowing Ar atmosphere to form and coat ZrB₂ on the carbon fibres in situ by carbothermal reaction. Microstructural observation of infiltrated porous C/C composites revealed carbon fibres coating with fine nanosized (∼100 nm) ZrB₂ particles infiltrated to a depth exceeding 2 mm. Ultra high temperature ablation testing for 60 s at 2190 °C suggested formation of ZrO₂ around the inner bore of the downstream surface.     

Ti3Si(Al)C2-based ceramics fabricated by reactive melt infiltration with Al70Si30 alloy

Dense Ti₃Si(Al)C₂-based ceramics were synthesized using reactive melt infiltration (RMI) of Al₇₀Si₃₀ alloy into the porous TiC preforms. The effects of the infiltration temperature on the microstructure and mechanical properties of the synthesized composites were investigated. All the composites infiltrated at different temperatures were composed of Ti₃Si(Al)C₂, TiC, SiC, Ti(Al, Si)₃ and Al. With the increase of infiltration temperature from 1050 °C to 1500 °C, the Ti₃Si(Al)C₂ content increased to 52 vol.% and the TiC content decreased to 15 vol.%, and the Vickers hardness, flexural strength and fracture toughness of Ti₃Si(Al)C₂-based composite reached to 9.95 GPa, 328 MPa and 4.8 MPa m^1/2, respectively.     

A novel strategy for rapid fabrication of continuous carbon fiber reinforced (TiZrHfNbTa)C high-entropy ceramic composites: High-entropy alloy in-situ reactive melt infiltration

For the first time, dense continuous carbon fiber (C_f) reinforced (TiZrHfNbTa)C high-entropy ceramic (C_f/HEC) composites were rapidly prepared via in-situ reactive melt infiltration (RMI). A TiZrHfNbTa high-entropy alloy served as the cation source and carbon in C_f reinforced carbon matrix (C_f/C) preforms served as the anion source, and a (TiZrHfNbTa)C high-entropy ceramic phase with a near equimolar ratio was successfully formed. The results revealed that most of the TiZrHfNbTa high-entropy alloy reacted with the carbon matrix, and the harvested C_f/HEC composites exhibited an excellent bending strength (612.6 MPa) and low ablation rates. High reaction rates caused by ultra-high temperature and homogeneous distribution of elements in the high-entropy TiZrHfNbTa alloy significantly reduced the difference in reactivity with C among Ti, Zr, Hf, Nb, and Ta are considered to be the reasons for successful formation of (TiZrHfNbTa)C high-entropy ceramic with a near equimolar ratio in C_f/HEC composites.     

Microstructure and mechanical properties of Cf/ZrC composites fabricated by reactive melt infiltration at relatively low temperature

Carbon fiber-reinforced zirconium carbide matrix composites (C_f/ZrC) were prepared by vacuum infiltrating porous carbon/carbon preforms with molten Zr₂Cu alloy at 1200 °C. X-ray diffraction, scanning electron microcopy and transmission electron microscopy analysis were used to characterize the composition and microstructure of the final composites. It was found that the matrix of the composites were composed of the Cu–Zr–C amorphous phase dispersed with either single- or polycrystalline ZrC. Based on the microstructural analysis, the formation mechanism of the matrix was proposed to be a solution-precipitation and grain coalescence process. The influence of the heat treatment at 1800 °C was also investigated. Results indicated that at very high temperature the volatilization of residual metal somewhat deteriorated the flexural strength and the elastic modulus, but the fracture toughness of the composites was improved due to the sintering of ZrC grains.     

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.     

Ablation behavior of Cf/ZrC-SiC-based composites fabricated by an improved reactive melt infiltration

In this work, a highly dense C_f/ZrC-SiC-based composite is fabricated by an improved reactive melt infiltration (RMI). The ablation resistance of the composite is studied by air plasma test. The RMI-C_f/ZrC-SiC possesses a low porosity (3.49%) and high thermal conductivity. The dense microstructure can effectively retard oxygen from diffusing into the interior composite. Meanwhile, the high thermal conductivity makes the composite transfer heat timely during ablation, which reduces the heat accumulation on the ablation surface and weakens the thermal damage to the composite. Consequently, the as-fabricated composite exhibits an excellent ablation resistance. Compared to conventional PIP-C_f/ZrC-SiC composite, the linear and mass recession rates of the RMI-C_f/ZrC-SiC decline by 98.07% and 39.02% at a heat flux of 4.02 MW/m². Also, a continuous SiO₂-ZrO₂ layer forms on the sample surface, which isolates the sample surface from the plasma flame and protect the composites from further oxidation and ablation.