Diamond dispersed Si3N4 composites obtained by pulsed electric current sintering

30 vol.% 2 and 30 μm diamond dispersed Si3N4 matrix composites were prepared by pulsed electric current sintering (PECS) for 4 min at 100 MPa in the 1550-1750 °C range. The densification behaviour, microstructure, Si3N4 phase transformation and stiffness of the composites were assessed, as well as the thermal stability of the dispersed diamond phase. Monolithic Si3N4 with 4 wt% Al2O3 and 5 wt% Y2O3 sintering additives was fully densified at 1550 °C for 4 min and 60 MPa. The densification and α to β-Si3N4 transformation were substantially suppressed upon adding 30 vol.% diamond particles. Diamond graphitisation in the Si3N4 matrix was closely correlated to the sintering temperature and grit size. The dispersed coarse grained diamonds significantly improved the fracture toughness of the diamond composite, whereas the Vickers hardness was comparable to that of the Si3N4 matrix ceramic. The Elastic modulus measurements were found to be an excellent tool to assess diamond graphitisation in a Si3N4 matrix.