ß-sialon ceramics with TiN particle inclusions

Fully dense composites of 0–30 wt% discrete TiN particles distributed in a s-sialon matrix of overall composition Si 5·5 Al 0·5 O 0·5 N 7·5 have been prepared by hot isostatic pressing at 1650 and 1750°C. Pressureless sintering at 1775°C gave materials with an open porosity. Typical sizes of the TiN particles were 1–3 μm, and no intergranular glassy phase was observed in the prepared materials. The grain size of s-sialon was below 1 μm in the materials HIPed at 1650°C, and 1–2 μm at 1750°C. The Vickers hardness was fairly constant for the TiN-s-sialon composites with up to 15 wt% TiN added: H v 10 around 17·5 GPa for materials HIPed at 1650° and around 17 GPa at 1750°C, whereas at higher TiN contents the hardness decreased to around 16 GPa. The indentation fracture toughness of the s-sialon ceramic increased approximatively from 3 to 4 MPam 1 2 at an addition of 15 wt% TiN particulates. The fracture toughness could be further increased to 5 MPam 1 2 by addition of small amounts of Y 2 O 3 and A1N to a s-sialon composite with 30 wt% TiN.