Enhanced mechanical and dielectric properties of Si3N4−BN composite ceramics fabricated via reaction re-sinteirng process

Abstract

Dense Si3N4−BN composite ceramics were synthesized using reaction re-sintering method which involved an in-situ reactive sintering followed by a re-sintering process, employing Si3N4 and SiB6 powders as raw materials. Initially, SiB6 underwent nitridation to form Si3N4 and BN during the in suit reactive sintering. Subsequently, the pores between the Si3N4 and BN grains were significantly removed during the re-sintering stage, facilitating the strong integration of Si3N4 and BN grains within the composite ceramics. The re-sintering process significantly enhanced both the density and mechanical properties of the composite ceramics. The generated BN grains were uniformly distributed throughout the Si3N4 matrix, thereby improving both the machinability and dielectric properties. The composite ceramics with 20 wt.% BN demonstrated excellent mechanical and dielectric properties, characterized by a low apparent porosity of 3.8%, a high flexural strength of 315.6 MPa, a Vickers hardness of 5.0 GPa, a low dielectric constant of 5.02, and a loss tangent ranging from 1× 10-3 to 2.5 × 10-3 at frequencies between 8.2 and 12.4 GHz.