The fabrication of tungsten reinforced silicon nitride ceramics by altering nitrogen pressure

Abstract Due to high ductility, high-temperature melting, low thermal expansion coefficient, etc., tungsten (W) might be considered to be an ideal reinforcement in toughening or strengthening Si3N4 ceramics. However, it is difficult to fabricate W/Si3N4 composites due to the possible reactions between W and Si3N4 during sintering process at the high temperature. In this work, a novel way to avoid the reactions and fabricate the W/Si3N4 composites was proposed by thermodynamic analysis and verified by experiment. Firstly, the phase equilibrium between W and Si3N4 as a function of temperature and nitrogen pressure was thermodynamically calculated, which indicates that one critical nitrogen pressure exists for reactions between W and Si3N4 at a certain temperature. As the nitrogen pressure is higher than the critical value, the reactions would be inhibited or adversely proceeded. Based on the results, W was innovatively in-situ introduced in the form of WSi2 after sintering at 1750 °C under 50 bar nitrogen pressure. Moreover, the fracture toughness of Si3N4 ceramics was enhanced from 7.1 ± 0.2 to 8.0 ± 0.4 MPa m1/2, which proposes a new reinforcement or method in toughening Si3N4 ceramics.