Spark plasma sintering of silicon(oxy-)nitride/boron nitride composites and their subsequent thermo-physical properties

Silicon nitride and boron nitride (Si₃N₄/h-BN) based ceramic composites were prepared by Spark Plasma Sintering (SPS) using aluminium oxide (Al₂O₃) and/or yttrium oxide (Y₂O₃) as sintering additives. The amount of h-BN introduced varied from 0 vol.% to 20 vol.% in order to study its influence on ceramic properties. In the same way, the amount of oxide additives has been controlled and the influence of the additive's nature on the final properties has been underlined. The sintering temperature has been selected in order to obtain equivalent relative densities. The formation of β-SiAlON has been underlined by XRD and TEM analysis. Moreover, due to the fast-sintering process, amorphous secondary phase has been formed. Mechanical properties (hardness, fracture toughness, Young modulus) and thermal diffusivity have been evaluated. It appears that the nature of the oxide additive used plays an important role on the mechanical and thermal behaviour of Si₃N₄/h-BN composites.