Preparation of Si3N4 ceramics with high strength and high reliability via a processing strategy

In this study, the preparation of Si3N4 ceramics with high mechanical reliability is investigated. The influences of several processing steps on the bending strength and the Weibull modulus are reported including: (i) coating of the Si3N4 powder with its sintering aids, (ii) oxidation of the coated powder, (iii) cold isostatic pressing, (iv) gelcasting of the green bodies and (v) gas pressure sintering. It was found that all the aforementioned steps contribute to improvements of strength and reliability of Si3N4 ceramics. Via an optimised processing strategy, Si3N4 ceramics with a bending strength and a Weibull modulus as high as 944.7±29.5 MPa and 33.9, respectively, could be prepared. Additionally, it was also found that surface modifications, i.e. coating and oxidation of Si3N4 powder, increased the rheological properties of the powder suspension in aqueous media, which is favourable for in situ colloidal forming such as gelcasting.