Slip Casting and Pressureless Sintering of ZrB2-SiC Ceramics

The dispersion of ZrB2 particles in water was investigated using polyethyleneimine (PEI) as a dispersant. Results showed that the ZrB2 slurry had a isoelectric point of pH=5.7. The application of PEI changed the isoelectric point of the ZrB2 slurry to pH=11.5. High solids loading (45vol%) ZrB2-20vol% SiC slurries were prepared at pH=8.0 by adding 1.0wt% PEI. The green body prepared by slip casting had a relative density of 53%. The effects of boron as a sintering aid on the pressureless sintering process of the ZrB2-20vol% SiC ceramics were investigated. Nearly fully dense ZrB2- SiC composites were obtained by sintering at 2100 or 3 h. The sintered ceramics demonstrated a Vickers hardness of (17.5 .5)GPa, a flexure strength of (406 1)MPa,and a fracture toughness of (4.6 .4)MPa ¤m1/2.