Boron nitride microribbons strengthened and toughened alumina composite ceramics with excellent mechanical, dielectric, and thermal conductivity properties

Aluminum oxide (Al₂O₃) ceramics have been widely utilized as circuit substrates owing to their exceptional performance. In this study, boron nitride microribbon (BNMR)/Al₂O₃ composite ceramics are prepared using spark plasma sintering (SPS). This study examines the effect of varying the amount of toughened phase BNMR on the density, mechanical properties, dielectric constant, and thermal conductivity of BNMR/Al₂O₃ composite ceramics while also exploring the mechanisms behind the toughening and increased thermal conductivity of the fabricated ceramics. The results showed that for a BNMR content of 5 wt%, BNMR/Al₂O₃ composite ceramics displayed more enhanced characteristics than pure Al₂O₃ ceramics. In particular, the relative density, hardness, fracture toughness, and bending strength were 99.95%±0.025%, 34.11±1.5 GPa, 5.42±0.21 MPa·m^1/2, and 375±2.5 MPa, respectively. These values represent increases of 0.76%, 70%, 35%, and 25%, respectively, compared with the corresponding values for pure Al₂O₃ ceramics. Furthermore, during the SPS process, BNMRs are subjected to high temperatures and pressures, resulting in the bending and deformation of the Al₂O₃ matrix; this leads to the formation of special thermal pathways within it. The dielectric constant of the composite ceramics decreased by 25.6%, whereas the thermal conductivity increased by 45.6% compared with that of the pure Al₂O₃ ceramics. The results of this study provide valuable insights into ways of enhancing the performance of Al₂O₃-based ceramic substrates by incorporating novel BNMRs as a second phase. These improvements are significant for potential applications in circuit substrates and related fields that require high-performance materials with improved mechanical properties and thermal conductivities.