Novel accordion structure Ti₃C₂–Ni_0.5Zn_0.5Fe₂O₄composites with nice electromagnetic wave absorption properties.

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 °C, 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 MP·m^1/2), Vickers hardness (16.3 GPa), and thermal conductivity (15.8 W/(m·K)) of the SiC/Al₄SiC₄ composite sintered at 1650 °C were significantly higher than the hardness (13.2 GPa), fracture toughness (2.16 MPa·m^1/2), 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.

High strength SiC whisker-reinforced Ti₃SiC₂ composites (SiC_w/Ti₃SiC₂) with an improved thermal conductivity and mechanical properties were fabricated by spark plasma sintering. The bending strength of 10 wt% SiC_w/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% SiC_w. This remarkable improvement both in mechanical and thermal properties was attributed to the fine-grained uniform composite microstructure along with the effects of incorporated SiC_w. The SiC_w/Ti₃SiC₂ can be a feasible candidate for the in-core structural application in nuclear reactors due to the excellent mechanical and thermal properties.

A novel Y₃Si₂C₂ material was synthesized at a relatively low temperature (900 °C) using a molten salt method for the first time, and subsequently used as the joining material for carbon fiber reinforced SiC (C_f/SiC) composites. The sound near-seamless joints with no obvious remaining interlayer were obtained at 1600 °C 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 C_f/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 °C for 10 min. The failure of the joints occurred in the C_f/SiC matrix, indicating that the interface was stronger than that of the C_f/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.