Effects of copper on microstructure and mechanical properties of Cf/ZrC composites fabricated by low-temperature liquid metal infiltration

Carbon fiber-reinforced zirconium carbide matrix (C_f/ZrC) composites were fabricated by a liquid metal infiltration process at 1200 °C, using low melting Zr₇Cu₁₀, ZrCu and Zr₂Cu alloys as infiltrators. The effects of Cu on microstructure and mechanical properties of the composites were investigated. The results indicated that the products were composed of either single- or polycrystalline ZrC, C and Cu. With increasing Cu content in the infiltrators, the yield of ZrC decreased from 43.7 vol% to 27.9 vol%. When ZrCu was used as an infiltrator, the obtained composites exhibited a better bending strength of 98.2±3.1 MPa. What is more, the use of Zr₂Cu could provide the highest fracture toughness of the composites with a moderate debonding.     

Effect of Cu on the ablation properties of Cf/ZrC composites fabricated by infiltrating Cf/C preforms with Zr-Cu alloys

C_f/ZrC composites were fabricated by reactive melt infiltration at 1200 °C, Low melting Zr₇Cu₁₀, ZrCu and Zr₂Cu alloys were used as infiltrators and the effect of Cu on ablation properties of the composites was investigated. The results show that the C_f/ZrC composites exhibit excellent anti-ablative properties affected apparently by the Cu contents. With the increase of Cu in infiltrators, the linear recession rates decrease from 0.0019±0.0006 to −0.0006±0.0002 mm s⁻¹, whereas the mass loss rates increase from 0.0006±0.0003 to 0.0047±0.0009 g s⁻¹. The formation of a dense ZrO₂ protective layer and the evaporation of residual Cu are in favor of their ablation resistance.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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%.     

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.     

Properties regulation of SiC ceramics prepared via stereolithography combined with reactive melt infiltration techniques

Stereolithography(SLA) combined with reactive melt infiltration (RMI) is an effective way to fabricate silicon carbide(SiC) ceramic components with complex shapes and high precision. The purpose of this paper is to increase the content of SiC in the sintered body and improve the properties of SiC ceramics prepared by SLA/RMI technologies by the impregnation of the precursor of carbon source after debinding. The effects of the concentration of phenolic resin solution on the strength of sintered body were studied. The results show that this method can reduce the coefficient of thermal expansion and improve the thermal conductivity of the final body. At the same time, when the concentration of phenolic resin solution is 40 wt%, the final body obtained the best comprehensive properties. The value of bulk density, flexural strength and elastic modulus were 2.89 g/cm³, 244.17 ± 5.13 MPa and 402.39 GPa, respectively. This strategy provides a promising prospect for the preparation of space optical mirrors with complex shapes and high strength by the SLA/RMI method.     

Microstructure and properties of Cu-Ti alloy infiltrated chopped Cf reinforced ceramics composites

Novel friction composites (C/C-Cu₅Si-TiC) were prepared via reactive melt infiltration (RMI) of Cu-Ti alloy into porous C/C-SiC composites. The microstructure, physical properties and tribological behaviors of the novel material were studied. Results were compared to conventional C/C-SiC composites produced by liquid silicon infiltration(LSI). The resultant composite showed the microstructure composed of Cu₅Si matrix reinforced with TiC particles and intact C/C structures. Most importantly, the composite did not present traces of free Si. As a result, the C/C-Cu₅Si-TiC composite showed higher flexural strength, impact toughness and thermal diffusivity in comparison to C/C-SiC composites. Tribological properties were measured using 30CrSiMoVA as a counterpart. In general, the C/C-Cu₅Si-TiC composites showed lower coefficient of friction(COF), but higher wear resistance and frictional stability. The improved wear resistance of the C/C-Cu₅Si-TiC composites is credited to the formation of friction films from Cu₅Si matrix. Other deformation and wear mechanisms are also described considering the microstructural observations.     

Microstructure and mechanical properties of three-dimensional oxide/oxide composite fabricated by a slurry infiltration and sintering process

Oxide/oxide composites reinforced by two-dimensional fiber fabrics are important structural materials at high temperatures but exhibit low delamination resistance. This study developed a simple slurry infiltration and sintering (SIS) process to fabricate three-dimensional oxide/oxide composites. The results showed that a homogeneous microstructure in three directions was obtained. This composite possessed a weak matrix, which had a porous structure and low elastic modulus. Typical mechanical properties of the composite were not lower than those of two-dimensional oxide/oxide composites since the flexural strength and fracture toughness were 332.4 MPa and 11.6 MPa·m^1/2, respectively. Particularly, the composite had a good interlaminar shear strength of 25.4 MPa and a superior transthickness tensile strength of 5.6 MPa. X-ray computed tomography showed that fiber yarns in the through-thickness direction effectively impeded crack propagation and enhanced delamination resistance. Therefore, the reported SIS process is a very promising method for manufacturing three-dimensional oxide/oxide composites.     

Synthesis and ultra-high temperature ablation behavior of a ZrC/Cr2AlC composite

This work reports on the fabrication and high temperature ablation property of a new ZrC/Cr₂AlC composite. The ZrC/Cr₂AlC composite was obtained by hot pressing a mixture of 15 vol% ZrC and 85 vol% Cr₂AlC powders at 1300 °C with 20 MPa for 1 h in Ar atmosphere. The composite had a flexural strength of 622 MPa, higher than 400 MPa for Cr₂AlC. The high temperature ablation behavior of the composite was investigated using the oxyacetylene torch ablation test. During oxyacetylene torch testing, the composite underwent a series of thermal decomposition and oxidation. Microstructure and composition of the synthesized composite before and after the ablation test were characterized with scanning electron microscopy and X-ray diffractometry techniques.     

C/SiC–ZrB2–ZrC composites fabricated by reactive melt infiltration with ZrSi2 alloy

C/SiC–ZrB₂–ZrC composites were prepared by reactive melt infiltration (RMI) combined with vacuum pressure impregnation (VPI) method. B₄C–C was first introduced into C/SiC composites with a porosity of about 30% by impregnating the mixture of B₄C and phenol formaldehyde resin, followed by pyrolysis at 900 °C. The molten ZrSi₂ alloy was then infiltrated into the porous C/SiC–B₄C–C to obtain C/SiC–ZrB₂–ZrC composites. The flexural strength was tested. The ablation behavior was investigated under an oxyacetylene torch flame. It has been found that the C/SiC–ZrB₂–ZrC showed a high flexural strength and an excellent ablation resistance. The reactions between ZrSi₂ alloy and B₄C–C were studied, and a model based on these reactions was built up to describe the formation mechanism of the matrix.     

Tough and wear-resistant carbon fiber reinforced TiC-based composite prepared by alloyed melt infiltration at low temperatures

To improve the toughness and friction properties of carbon fiber reinforced ceramic matrix composite, a Cu alloy modified carbon fiber reinforced TiC based ceramic matrix composite was designed and prepared by TiCu alloy melt infiltration at low temperatures up to 1100 °C. The as-produced composite was mainly composed of carbon, TiC, Ti₃Cu₄, TiCu₄ and Cu phases. Due to the ductile Cu alloy introduced into the matrix, the composite showed good mechanical performance especially the fracture toughness. The flexural strength reached about 248.36 MPa while the fracture toughness was up to 15.78 MPa·m^1/2. The high toughness of the composite was mainly attributed to the fiber bridging, fiber pull-out, interface debonding, crack propagation and deflection. The tribological performance of the as-produced composite was measured using SiC and 440C stainless steel balls as counterparts, respectively. The as-prepared composite exhibited good wear resistance and the wear mechanism was discussed based on the microstructural observations.     

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.     

Microstructure and mechanical properties of ZTA composites fabricated by oscillatory pressure sintering

The influence of sintering temperature on the microstructure and mechanical properties of Al₂O₃?20 wt% ZrO₂ composites fabricated by oscillatory pressure sintering (OPS) was investigated by means of X-ray diffraction, scanning electron microscopy, three-point bending test and Vickers indentation. Results were compared to specimens obtained by conventional hot pressing (HP) under a similar sintering schedule. The optimum oscillatory pressure sintering temperature was found to be 1600 °C; almost fully dense materials (99.94% of theoretical density) with homogeneous microstructure could be achieved. The highest flexural strength, fracture toughness and hardness of such composites reached 1145 MPa, 5.74 MPa m^1/2 and 19.08 GPa when sintered at 1600 °C, respectively. Furthermore, the oscillatory pressure sintering temperature could be decreased by more than 50 °C as compared with the HP method, OPS favouring enhanced grain boundary sliding, plastic deformation and diffusion in the sintering process.