Defects control of silicon nitride ceramics by oscillatory pressure sintering and consequent hot isotropic pressing

Micro-pores and micro-cracks inhibit the enhancement in strength and toughness of structural ceramics. Among various processing procedures, sintering is the key stage to control microstructure and then enhance mechanical performances of ceramics. Here, we reported the consolation of silicon nitride ceramics with high strength and toughness by defects control, using oscillatory pressure sintering (OPS) followed by hot isostatic pressing (HIP) techniques. The introduction of oscillatory pressure and isostatic pressure may enhance grain sliding and grains deformation of during sintering, thus removed the trapped pores at grain boundaries and accelerated growth of beta-Si3N4 grains. Because of the microstructure evolution, the Si3N4 ceramics exhibited flexural strength of 1630 +/- 21 MPa and fracture toughness of 7.1 +/- 0.6 MPa m1/2 when sintered at 1750 degrees C. Thus, this work provides a path to prepare ultra-strong and tough ceramics by controlling various micro-defects.