Jimei Xue

This study comprehensively investigates the damage evolution and property degradation of SiC _f /Si ₃ N ₄ composites subjected to high‐speed waterjet impacts simulating rain erosion. The composites are fabricated by CVI using SiC fiber fabric preform with BN interface and Si ₃ N ₄ matrix. A single‐jet device generates stable waterjets (≈350 m/s, ≈4.9 mm diameter) to induce controlled erosion damage. Results demonstrate a staged progression of erosion damage: initial localized fiber bundle fracture and matrix cracking (0%–25% depth) is followed by pit widening via water‐wedging and delamination (25%–75% depth), culminating in penetration with a stabilized damage area (>75% depth). Tensile strength decreases by 47.5% after full penetration, with AE analysis indicating a transition from synergistic fiber‐matrix failure to a fiber‐dominated quasi‐brittle fracture mechanism due to interfacial weakening and matrix damage. Conversely, electromagnetic analysis shows that the erosion‐induced damage, including pits, cracks, and increased porosity, improved impedance matching. This leads to a significant enhancement in wave‐absorbing performance, with the minimum reflection loss decreasing from −5.96 dB for undamaged material to below −7 dB for fully eroded specimen across the X‐band. This work elucidates the dual influences of rain erosion on the mechanical and electromagnetic functionality of SiC _f /Si ₃ N ₄ composites, providing critical insights for aerospace applications.)

Oxide ceramic matrix composites (OCMC) have good high‐temperature resistance, oxidation resistance, and mechanical properties. However, the microwave absorbing properties of OCMC areinsufficient due to the low dielectric and low loss characteristics of oxide ceramics, so it is urgent to develop a kind of the oxide ceramic matrix with adjustable microstructure and electromagnetic properties. PDC‐SiOC ceramics are the optimal oxide ceramics whose component and microstructure can be adjusted by rare earth nitrate modified polysiloxane precursor. For Sc(NO₃)₃ modified PDC‐SiOC ceramics, rare earth metals not only can react with siloxy groups to form silicates at high temperatures but also can catalyze the formation of SiCnws. Herein, rare earth nitrate modified polysiloxane precursor was pyrolyzed at 900°C, and then annealing at high temperature to form silicate and SiCnws. After annealing at 1400°C, a large amount SiCnws was in situ formed conductive network structure in SiOC ceramic, so the SiOC ceramic with SiCnws had great electromagnetic wave (EMW) absorbing properties, the maximum effective absorption bandwidth (EAB_max) and the minimum reflection coefficient (RC_min) at the thickness of 2.75 mm reach 4.0 GHz and −42.3 dB in X‐band, respectively. By the double‐layer impedance matching design, the EAB can be effectively improved, which provide a good way for the design and fabrication of OCMC with advanced (EMW) absorbing properties.

A kind of chemical vapor infiltration (CVI) Si₃N₄–BN–SiCN composite ceramic with excellent electromagnetic wave (EMW) absorbing properties is obtained by CVI BN interface and SiCN matrix on porous Si₃N₄ ceramics, and then annealed at high temperatures (1200°C‐1500°C) in N₂ atmosphere. The crystallization behavior, EMW absorbing mechanism and mechanical properties of the composite ceramics have been investigated. Results showed CVI SiCN ceramics with BN interface were crystallized in the form of nanograins, and the crystallization temperature was lower. Moreover, both EMW absorbing properties and mechanical properties of CVI Si₃N₄–BN–SiCN composite ceramics firstly increased and then decreased with the increase in annealing temperature due to the influence of BN interface on the microstructure and phase composition of the composite ceramics. The minimum reflection coefficient (RC) and maximum effective absorption bandwidth (EAB) of the composite ceramics annealed at 1300°C were −47.05 dB at the thickness of 4.05 mm and 3.70 GHz at the thickness of 3.65 mm, respectively. The flexural strength and fracture toughness of the composite ceramics annealed at 1300°C were 94 MPa and 1.78 MPa/m^1/2, respectively.