Open Access Research Article Issue
Fabrication and mechanical behavior of 2D-Cf/TaxHf1−xC–SiC composites by a low-temperature and highly-efficient route
Journal of Advanced Ceramics 2023, 12 (10): 1961-1972
Published: 19 October 2023
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Cf/TaxHf1−xC–SiC composites are ideal thermal structural materials for service under extreme conditions of hypersonic vehicles. However, how to synthesize TaxHf1-xC powders and efficiently fabricate Cf/TaxHf1-xC–SiC composites still faces some challenges. Furthermore, mechanical properties and thermophysical properties of TaxHf1−xC vary with the composition, but not monotonically. In-depth analysis of mechanical behaviors of the Cf/TaxHf1−xC–SiC composites is extremely important for their development and applications. In this study, the TaxHf1−xC powders (x = 0.2, 0.5, 0.8) were successfully synthesized via solid solution of TaC and HfC at a relatively low temperature of 1800 ℃, with a small amount of Si as an additive. Subsequently, the efficient fabrication of 2D-Cf/TaxHf1–xC–SiC composites was achieved by slurry impregnation and lamination (SIL) combined with precursor infiltration and pyrolysis (PIP). In addition, the mechanical behavior of the composites was investigated systematically. It is demonstrated that the composites present remarkable non-brittle fractures, including a large number of fiber pull out and interphase debonding. Also, the fracture failure involves a complex process of microcrack generation and propagation, matrix cracking, and layer fracture. Moreover, the interfacial bonding between the fibers and the matrix is enhanced as the Ta∶Hf ratio decreases from 4∶1 to 1∶4. As a result, Cf/Ta0.2Hf0.8C–SiC composites exhibit exceptional flexural strength of 437±19 MPa, improved by 46% compared with Cf/Ta0.8Hf0.2C–SiC (299±19 MPa). This study provides a new perception of design and fabrication of ultra-high-temperature ceramic (UHTC) matrix composites with high performance.

Open Access Research Article Issue
Effects of interfacial residual stress on mechanical behavior of SiCf/SiC composites
Journal of Advanced Ceramics 2022, 11 (1): 94-104
Published: 28 October 2021
Abstract PDF (4.2 MB) Collect

Layer-structured interphase, existing between reinforcing fiber and ceramics matrix, is an indispensable constituent for fiber-reinforced ceramic composites due to its determinant role in the mechanical behavior of the composites. However, the interphase may suffer high residual stress because of the mismatch of thermal expansion coefficients in the constituents, and this can exert significant influence on the mechanical behavior of the composites. Here, the residual stress in the boron nitride (BN) interphase of continuous SiC fiber-reinforced SiC composites was measured using a micro-Raman spectrometer. The effects of the residual stress on the mechanical behavior of the composites were investigated by correlating the residual stress with the mechanical properties of the composites. The results indicate that the residual stress increases from 26.5 to 82.6 MPa in tension as the fabrication temperature of the composites rises from 1500 to 1650 ℃. Moreover, the increasing tensile residual stress leads to significant variation of tensile strain, tensile strength, and fiber/matrix debonding mode of the composites. The sublayer slipping of the interphase caused by the residual stress should be responsible for the transformation of the mechanical behavior. This work can offer important guidance for residual stress adjustment in fiber-reinforced ceramic composites.

Open Access Research Article Issue
Fabrication and microstructure evolution of Csf/ZrB2-SiC composites via direct ink writing and reactive melt infiltration
Journal of Advanced Ceramics 2021, 10 (6): 1371-1380
Published: 30 September 2021
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Fiber damage and uniform interphase preparation are the main challenges in conventional short fiber reinforced ceramic matrix composites. In this work, we develop a novel processing route in fabrication of short carbon fiber reinforced ZrB2-SiC composites (Csf/ZrB2-SiC) overcoming the above two issues. At first, Csf preforms with oriented designation and uniform PyC/SiC interphase are fabricated via direct ink writing (DIW) of short carbon fiber paste followed by chemical vapor infiltration. After that, ZrB2 and SiC are introduced into the preforms by slurry impregnation and reactive melt infiltration, respectively. Microstructure evolution and optimization of the composites during fabrication are investigated in detail. The as-fabricated Csf/ZrB2-SiC composites have a bulk density of 2.47 g/cm3, with uniform weak interphase and without serious fiber damage. Consequently, non-brittle fracture occurs in the Csf/ZrB2-SiC composites with widespread toughening mechanisms such as crack deflection and bridging, interphase debonding, and fiber pull-out. This work provides a new opportunity to the material design and selection of short fiber reinforced composites.

Open Access Research Article Issue
Effect of BNNTs/matrix interface tailoring on toughness and fracture morphology of hierarchical SiCf/SiC composites
Journal of Advanced Ceramics 2019, 8 (4): 555-563
Published: 04 December 2019
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A thin BN interphase is applied on BNNTs surface to tailor the interfacial bonding between BNNTs and SiC matrix in hierarchical SiCf/SiC composites. The thickness of BN interphase ranging from 10 to 70 nm can be optimized by chemical vapor deposition after BNNTs are in situ grown on SiC fiber surface. Without BN interphase, the fracture toughness of hierarchical SiCf/SiC composites can be impaired by 13.6% due to strong interfacial bonding. As long as BN interphase with 30-45 nm thickness is applied, the interfacial bonding can be optimized and fracture toughness of hierarchical composites can be improved by 27.3%. It implies that tailoring BNNTs/matrix interface by depositing a layer of BN interphase is in favor of activating energy dissipation mechanisms at nanoscale induced by BNNTs.

Open Access Research Article Issue
3D Cf/SiBCN composites prepared by an improved polymer infiltration and pyrolysis
Journal of Advanced Ceramics 2018, 7 (3): 266-275
Published: 10 October 2018
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Using liquid poly(methylvinyl)borosilazanes (PMVBSZ) as precursor, carbon fiber reinforced SiBCN matrix composites (Cf/SiBCN) were fabricated by a modified polymer infiltration and pyrolysis (PIP) process. With dicumyl peroxide added as cross-linking agent, the PMVBSZ could be solidified at a low temperature of 120 ℃, leading to a high ceramic yield of ~70%. The cross-linking mechanism and ceramization processes of the precursor were investigated in detail. Moreover, a modified infiltration technology was developed, which improved the efficiency and protected the precursor against moist air during PIP. Consequently, the obtained Cf/SiBCN composites had an oxygen content of around 1.22 wt%. Benefiting from the high ceramic yield and high efficiency of the modified PIP, Cf/SiBCN composites with an open porosity of ~10% and uniform microstructure were obtained after only 7 cycles of PIP. The flexural strength and fracture toughness of the derived Cf/SiBCN composites were 371 MPa and 12.9 MPa·m1/2, respectively. This work provides a potential route for the fabrication of high performance Cf/SiBCN composites.

Open Access Research Article Issue
Fabrication and microstructure of ZrB2–ZrC–SiC coatings on C/C composites by reactive melt infiltration using ZrSi2 alloy
Journal of Advanced Ceramics 2018, 7 (1): 64-71
Published: 20 January 2018
Abstract PDF (1.4 MB) Collect

ZrB2–ZrC–SiC ternary coatings on C/C composites are investigated by reactive melt infiltration of ZrSi2 alloy into pre-coatings. Two different pre-coating structures, including porous B4C–C and dense C/B, are designed by slurry dip and chemical vapor deposition (CVD) process respectively. The coating prepared by reactive melt infiltration (RMI) into B4C–C presents a flat and smooth surface with a three-layer cross-sectional structure, namely interior SiC transition layer, gradient ZrB2–ZrC–SiC layer, and ZrB2–ZrC exterior layer. In comparison, the coating prepared by RMI into C/B shows a more granular surface with a different three-layer cross-sectional structure, interior unreacted B–C pre-coating layer, middle SiC layer, and exterior ZrB2–ZrC–ZrSi2 layer. The forming mechanisms of the specific microstructures in two coatings are also investigated and discussed in detail.

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