Near-net shape manufacture of B4C-Co and ZrC-Co composites by slip casting and pressureless sintering

Fabrication of near-net shaped B4C-Co and ZrC-Co composites by slip casting and pressureless sintering is described. It is shown how B4C-Co and ZrC-Co concentrated suspensions can be prepared by aqueous colloidal processing, and optimized (in terms of pH, deflocculant contents, and sonication time) to have a shear-thinning rheological behaviour suitable for the near-net shaping of the corresponding cermet compacts by slip casting. It is also demonstrated that the robust, highly-dense compacts so obtained have a uniform green microstructure without macro-defects or gradient density, and which can be fully densified by pressureless sintering. Specifically, it is shown that B4C-Co compacts densify by reactive and transient liquid-phase sintering, thus resulting in multi-component ceramics. ZrC-Co compacts densify however by persistent liquid-phase sintering, thus resulting in cermets. An explanation is given for these observations, and general implications are discussed for the near-net shape manufacture of these and similar carbide-metal composites for use in engineering applications.