Microstructure and EMW absorption properties of CVI Si 3 N 4 –Si CN ceramics with BN interface annealed in N 2 atmosphere

A kind of chemical vapor infiltration ( CVI ) Si 3 N 4 – BN –Si CN composite ceramic with excellent electromagnetic wave ( EMW ) absorbing properties is obtained by CVI BN interface and Si CN matrix on porous Si 3 N 4 ceramics, and then annealed at high temperatures (1200°C‐1500°C) in N 2 atmosphere. The crystallization behavior, EMW absorbing mechanism and mechanical properties of the composite ceramics have been investigated. Results showed CVI Si CN 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 Si 3 N 4 – BN –Si CN 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 GH z at the thickness of 3.65 mm, respectively. The flexural strength and fracture toughness of the composite ceramics annealed at 1300°C were 94 MP a and 1.78 MP a/m 1/2 , respectively.