BETA-SIALON CERAMICS WITH TIN PARTICLE INCLUSIONS

Fully dense composites of 0-30 wt% discrete TiN particles distributed in a beta-sialon matrix of overall composition Si5.5Al0.5O0.5N7.5 have been prepared by hot isostatic pressing at 1650 and 1750-degrees-C Pressureless sintering al 1775-degrees-C gave materials with an open porosity. Typical sizes of the TiN particles were 1-3 mum, and no intergranular glassy phase was observed in the prepared materials. The grain size of beta-sialon was below 1 mum in the materials HIPed at 1650-degrees-C, and 1-2 mum at 1750-degrees-C The Vickers hardness was fairly constant for the TiN-beta-sialon composites with up to 15 wt% TiN added H(V)10 around 17.5 GPa for materials HIPed at 1650-degrees and around 17 GPa at 1750-degrees-C, whereas at higher TiN contents the hardness decreased to around 16 GPa. The indentation fracture toughness of the beta-sialon ceramic increased approximatively from 3 to 4 MPam1/2 at an addition of 15 wt% TiN particulates. The fracture toughness could be further increased to 5 MPam1/2 by addition of small amounts of Y2O3 and A1N to a beta-sialon composite with 30 wt% TiN.