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

Si3N4 ceramic substrates serving as heat dissipater and supporting component are required to have excellent thermal and mechanical properties. To prepare Si3N4 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 degrees 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 Si3N4 particles' rearrangement and alpha -> B transformation rate. Furthermore, the densification process for the Si3N4 ceramics prepared via the two-step gas-pressure sintering was revealed. After sintered at 1525 degrees C for 3 h followed by a high-temperature sintering at 1850 degrees C for another 3 h, the prepared Si3N4 compact with a bimodal microstructure presented the highest thermal conductivity and flexural strength of 79.42 W center dot m- 1 center dot K-1 and 801 MPa, respectively, which holds great application prospects as ceramic substrates.