Fabrication of Si3N4 ceramics with high thermal conductivity and flexural strength via novel two-step gas-pressure sintering

Si 3 N 4 ceramic substrates serving as heat dissipater and supporting component are required to have excellent thermal and mechanical properties. To prepare Si 3 N 4 with desirable properties, a novel two-step gas-pressure sintering route including a pre-sintering step followed by a high-temperature sintering step was devised. The effects of pre-sintering temperature (1500 – 1600 °C) on the phase transformation, microstructure, thermal and mechanical properties of the samples were studied. The pre-sintering temperature played an important role in adjusting the Si 3 N 4 particles’ rearrangement and α→β transformation rate. Furthermore, the densification process for the Si 3 N 4 ceramics prepared via the two-step gas-pressure sintering was revealed. After sintered at 1525 °C for 3 h followed by a high-temperature sintering at 1850 °C for another 3 h, the prepared Si 3 N 4 compact with a bimodal microstructure presented the highest thermal conductivity and flexural strength of 79.42 W·m −1 ·K −1 and 801 MPa, respectively, which holds great application prospects as ceramic substrates. • Si 3 N 4 with a bimodal microstructure was prepared by two-step gas-pressure sintering. • The α→β transformation rate can be tailored by the pre-sintering temperature. • The Si 3 N 4 pre-sintered at 1525 °C has the optimal comprehensive properties. • The prepared Si 3 N 4 holds great application prospects for ceramic substrates.