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Open Access Research Article Issue
Preparation and properties of Ti3SiC2-based corrosion mitigation coatings for SiCf/SiC PWR accident tolerant fuel cladding
Journal of Advanced Ceramics 2024, 13 (1): 73-85
Published: 22 January 2024
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To enhance the resistance of SiCf/SiC to hydrothermal corrosion in the pressurized water reactor (PWR) environment, structurally tunable Ti3SiC2-based corrosion mitigation coatings for SiCf/SiC were prepared using molten salt synthesis. The influence of various process parameters, such as Si/Ti molar ratio in raw materials, annealing time, and annealing temperature, on the phase composition and the structure of the coatings was explored. Through the process control, the fabricated coatings can be either Ti3SiC2 monolithic structure or TiC/Ti3SiC2 and TiC/Ti3SiC2/Ti5Si3Cx multi-layered structures. The coatings demonstrate strong bonding to the substrate due to in-situ reaction, exhibiting tensile and shear strength of at least 26.9 and 30.8 MPa, respectively. Incorporating TiC as a transition layer further enhances the tensile and shear strength to 41.3 and 51.4 MPa, respectively. Monolithic Ti3SiC2 coatings enhance the thermal conductivity of SiCf/SiC by 10%–12%. Notably, Ti3SiC2 coatings effectively protect SiCf/SiC from hydrothermal corrosion, demonstrating an 83% strength retention rate compared to 71% in the control group after corrosion. However, the Ti5Si3Cx layer exhibits unsatisfactory corrosion mitigation. The Ti3SiC2 monolithic coating has higher thermal conductivity, TiC/Ti3SiC2 multi-layered coating has higher bonding strength, and both have desirable resistance to the hydrothermal corrosion.

Open Access Review Issue
Long-term ceramic matrix composite for aeroengine
Journal of Advanced Ceramics 2022, 11 (9): 1343-1374
Published: 05 September 2022
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Three strategies were proposed to prolong the service life of continuous fiber-reinforced silicon carbide ceramic matrix composite (CMC-SiC), which served as thermal-structure components of aeroengine at thermo-mechanical-oxygenic coupling environment. As for some thermal-structure components with low working stress, improving the degree of densification was crucial to prolong the service life, and the related process approaches were recited. If the thermal-structure components worked under moderate stress, the matrix cracking stress (σmc) should be improved as far as possible. The fiber preform architecture, interface shear strength, residual thermal stress, and matrix strengthening were associated with σmc in this review. Introducing self-healing components was quite significant with the appearance of matrix microcracks when CMC-SiC worked at more severe environment for hundreds of hours. The damage can be sealed by glass phase originating from the reaction between self-healing components and oxygen. The effective self-healing temperature range of different self-healing components was first summarized and distinguished. The structure, composition, and preparation process of CMC-SiC should be systematically designed and optimized to achieve long duration target.

Open Access Research Article Issue
Formation of nanocrystalline graphite in polymer-derived SiCN by polymer infiltration and pyrolysis at a low temperature
Journal of Advanced Ceramics 2021, 10 (6): 1256-1272
Published: 29 August 2021
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The microstructure of polymer-derived ceramics (PDCs) was closely related to processing. This study demonstrated that SiCN matrix prepared by polymer infiltration and pyrolysis (PIP) at 900 ℃ inside a Si3N4 whisker (Si3N4w) preform with submicro-sized pores differed from its powder- consolidated analogue in both the content and structure of free carbon. Chemical analysis showed that PIP process had a higher free carbon yield. Raman spectroscopy and transmission electron microscopy (TEM) observation discovered a higher graphitization degree of free carbon and the existence of nanocrystalline graphite in SiCN matrix. Dielectric properties of Si3N4w/SiCN composites were greatly enhanced when volume fraction of SiCN matrix reached 24.5% due to dielectric percolation caused by highly-lossy free carbon. Reconsolidation of hydrocarbon released during pyrolysis by gas-state carbonization in Si3N4 whisker preform was supposed to account for the high yield and graphitization degree of free carbon in PIP process.

Open Access Research Article Issue
Enhanced mechanical property and tunable dielectric property of SiCf/SiC-SiBCN composites by CVI combined with PIP
Journal of Advanced Ceramics 2021, 10 (4): 758-767
Published: 05 August 2021
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The SiBCN matrix via chemical vapor infiltration (CVI) or/and polymer infiltration pyrolysis (PIP) technologies was orderly introduced to SiCf/SiC composites to optimize the mechanical property and electromagnetic (EM) shielding effectiveness simultaneously. The BN interface with the thickness of 350 nm was designed to obtain a little stronger interface bonding. The flexural strength of SiCf/SiC-SiBCN composites reached 545.45±29.59 MPa thanks to the crack deflection between the CVI SiC and CVI SiBCN, as well as CVI SiBCN and PIP SiBCN matrix because of the modulus difference between them. The fracture toughness (KIC) with the value of 16.02±0.94 MPa·m1/2 was obtained owing to the extension of crack propagation path. The adverse effect of stronger interface bonding was eliminated by the design of matrix microstructure for SiCf/SiC-SiBCN composites. The thermal conductivity in the thickness direction was 7.64 W·(m·K)-1 at 1200 ℃ and the electric resistivity decreased to 1.53×103 Ω·m. The tunable dielectric property was obtained with the coordination of wave-absorption CVI SiBCN matrix and impedance matching PIP SiBCN matrix, and the total shielding effectiveness (SET) attained 30.01 dB. It indicates that the SiCf/SiC-SiBCN composites have great potential to be applied as structural and functional materials.

Open Access Research Article Issue
Mechanical and dielectric properties of porous and wave-transparent Si3N4-Si3N4 composite ceramics fabricated by 3D printing combined with chemical vapor infiltration
Journal of Advanced Ceramics 2019, 8 (3): 399-407
Published: 03 August 2019
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Porous Si3N4-Si3N4 composite ceramics were fabricated by 3D printing combined with low-pressure chemical vapor infiltration (CVI). This technique could effectively improve the designability of porous Si3N4 ceramics and optimize the mechanical and dielectric properties. The effects of process parameters including the deposition time and heat treatment on the microstructure and properties of porous Si3N4-Si3N4 composite ceramics were studied. The study highlights following: When CVI processing time was increased from 0 to 12 h, the porosity decreased from 68.65% to 26.07% and the density increased from 0.99 to 2.02 g/cm3. At the same time, the dielectric constant gradually increased from 1.72 to 3.60; however, the dielectric loss always remained less than 0.01, indicating the excellent electromagnetic (EM) wave-transparent performance of porous Si3N4-Si3N4 composite ceramics. The maximum flexural strength of 47±2 MPa was achieved when the deposition time attained 6 h. After heat treatment, the porosity increased from 26.07% to 36.02% and the dielectric constant got a slight increase from 3.60 to 3.70 with the dielectric loss still maintaining lower than 0.01. It has been demonstrated that the porous Si3N4-Si3N4 composite ceramics are a promising structural and EM wave-transparent material suitable for high temperature service.

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