Influence of hot-press sintering parameters on microstructures and mechanical properties of h-BN ceramics

• Amorphous or nanocrystalline h-BN grains can be obtained through ball milling process.
• Sintering parameters are the key factors that affect the microstructures and mechanical properties of h-BN ceramic.
• A relative low sintering temperature can prevent grain growth and improve the mechanical properties.

Pure h-BN ceramics were processed at different sintering temperatures and hold times using ball milled nanocrystalline or amorphous h-BN powders. Increases in sintering temperature induced greater grain growth but reduced relative densities and mechanical properties. Changes in sintering hold times caused further increases in grain sizes and relative density, but had little impact on mechanical properties. The grain sizes play an important aspect of strength in h-BN ceramics. The relationship of flexural strength and grain sizes in h-BN ceramics conforms to Hall-Petch behavior. When the grain size of h-BN ceramics increased from 0.3 μm to 8 μm, the flexural strength declined from 163 ± 6 to 84 ± 4 MPa. The mechanical properties of h-BN ceramics depend both on relative densities and grain sizes.