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Open Access Research Article Issue
High-entropy rare-earth diborodicarbide: A novel class of high-entropy (Y0.25Yb0.25Dy0.25Er0.25)B2C2 ceramics
Journal of Advanced Ceramics 2023, 12 (7): 1430-1440
Published: 19 June 2023
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A novel class of high-entropy rare-earth metal diborodicarbide (Y0.25Yb0.25Dy0.25Er0.25)B2C2 (HE-REB2C2) ceramics was successfully fabricated using the in-situ reactive spark plasma sintering (SPS) technology for the first time. Single solid solution with a typical tetragonal structure was formed, having a homogeneous distribution of four rare-earth elements, such as Y, Yb, Dy, and Er. Coefficients of thermal expansion (CTEs) along the a and c directions (αa and αc) were determined to be 4.18 and 16.06 μK−1, respectively. Thermal expansion anisotropy of the as-obtained HE-REB2C2 was attributed to anisotropy of the crystal structure of HE-REB2C2. The thermal conductivity (k) of HE-REB2C2 was 9.2±0.09 W·m−1·K−1, which was lower than that of YB2C2 (19.2±0.07 W·m−1·K−1), DyB2C2 (11.9±0.06 W·m−1·K−1), and ErB2C2 (12.1±0.03 W·m−1·K−1), due to high-entropy effect and sluggish diffusion effect of high-entropy ceramics (HECs). Furthermore, Vickers hardness of HE-REB2C2 was slightly higher than that of REB2C2 owing to the solid solution hardening mechanism of HECs. Typical nano-laminated fracture morphologies, such as kink boundaries, delamination, and slipping were observed at the tip of Vickers indents, suggesting ductile behavior of HE-REB2C2. This newly investigated class of ductile HE-REB2C2 ceramics expanded the family of HECs to diboridcarbide compounds, which can lead to more research works on high-entropy rare-earth diboridcarbides in the near future.

Open Access Research Article Issue
Near-seamless joining of Cf/SiC composites using Y3Si2C2 via electric field-assisted sintering technique
Journal of Advanced Ceramics 2022, 11 (8): 1196-1207
Published: 18 July 2022
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A novel Y3Si2C2 material was synthesized at a relatively low temperature (900 ℃) using a molten salt method for the first time, and subsequently used as the joining material for carbon fiber reinforced SiC (Cf/SiC) composites. The sound near-seamless joints with no obvious remaining interlayer were obtained at 1600 ℃ using an electric field-assisted sintering technique (FAST). During joining, a liquid phase was formed by the eutectic reaction among Y3Si2C2, γ(Y-C) phase, and SiC, followed by the precipitation of SiC particles. The presence of the liquid promoted the sintering of newly formed SiC particles, leading to their complete consolidation with the Cf/SiC matrix. On the other hand, the excess of the liquid was pushed away from the joining area under the effect of a uniaxial pressure of 30 MPa, leading to the formation of the near-seamless joints. The highest shear strength (τ) of 17.2±2.9 MPa was obtained after being joined at 1600 ℃ for 10 min. The failure of the joints occurred in the Cf/SiC matrix, indicating that the interface was stronger than that of the Cf/SiC matrix. The formation of a near-seamless joint minimizes the mismatch of thermal expansion coefficients and also irradiation-induced swelling, suggesting that the proposed joining strategy can be potentially applied to SiC-based ceramic matrix composites (CMCs) for extreme environmental applications.

Open Access Research Article Issue
Microstructure and properties of nano-laminated Y3Si2C2 ceramics fabricated via in situ reaction by spark plasma sintering
Journal of Advanced Ceramics 2021, 10 (3): 578-586
Published: 26 April 2021
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A nano-laminated Y3Si2C2 ceramic material was successfully synthesized via an in situ reaction between YH2 and SiC using spark plasma sintering technology. A MAX phase-like ternary layered structure of Y3Si2C2 was observed at the atomic-scale by high resolution transmission electron microscopy. The lattice parameters calculated from both X-ray diffraction and selected area electron diffraction patterns are in good agreement with the reported theoretical results. The nano-laminated fracture of kink boundaries, delamination, and slipping were observed at the tip of the Vickers indents. The elastic modulus and Vickers hardness of Y3Si2C2 ceramics (with 5.5 wt% Y2O3) sintered at 1500 ℃ were 156 and 6.4 GPa, respectively. The corresponding values of thermal and electrical conductivity were 13.7 W·m-1·K-1 and 6.3×105 S·m-1, respectively.

Open Access Research Article Issue
Fabrication of SiCw/Ti3SiC2 composites with improved thermal conductivity and mechanical properties using spark plasma sintering
Journal of Advanced Ceramics 2020, 9 (4): 462-470
Published: 09 July 2020
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High strength SiC whisker-reinforced Ti3SiC2 composites (SiCw/Ti3SiC2) with an improved thermal conductivity and mechanical properties were fabricated by spark plasma sintering. The bending strength of 10 wt% SiCw/Ti3SiC2 was 635 MPa, which was approximately 50% higher than that of the monolithic Ti3SiC2 (428 MPa). The Vickers hardness and thermal conductivity (k) also increased by 36% and 25%, respectively, from the monolithic Ti3SiC2 by the incorporation of 10 wt% SiCw. This remarkable improvement both in mechanical and thermal properties was attributed to the fine-grained uniform composite microstructure along with the effects of incorporated SiCw. The SiCw/Ti3SiC2 can be a feasible candidate for the in-core structural application in nuclear reactors due to the excellent mechanical and thermal properties.

Open Access Research Article Issue
Fabrication, microstructure, and properties of SiC/Al4SiC4 multiphase ceramics via an in-situ formed liquid phase sintering
Journal of Advanced Ceramics 2020, 9 (2): 193-203
Published: 07 April 2020
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The SiC/Al4SiC4 composites with the improved mechanical properties and thermal conductivity were fabricated by the in-situ reaction of polycarbosilane (PCS) and Al powders using spark plasma sintering. The addition of 5 wt% yttrium (Y) sintering additive was useful to obtain fully dense samples after sintering at a relatively low temperature of 1650 ℃, due to the formation of a liquid phase during sintering. The average particle size of the in-situ formed SiC was ~300 nm. The fracture toughness (4.9 MPa·m1/2), Vickers hardness (16.3 GPa), and thermal conductivity (15.8 W/(m·K)) of the SiC/Al4SiC4 composite sintered at 1650 ℃ were significantly higher than the hardness (13.2 GPa), fracture toughness (2.16 MPa·m1/2), and thermal conductivity (7.8 W/(m·K)) of the monolithic Al4SiC4 ceramics. The improved mechanical and thermal properties of the composites were attributed to the high density, fine grain size, as well as the optimized grain boundary structure of the SiC/Al4SiC4 composites.

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