Sintering ZrO2/TiC composites with TiH2. The role of transient liquid phase and of substoichiometry

Sintering tetragonal ZrO2 with 35 vol-% TiC results in a microstructure where all grain facets are free of amorphous interfaces independent of sintering aids as TiH2 or MgO/Y2O3; grain sizes are below 1 mym. With substoichiometric TiC(1-x), a relative density of 95 % and closed porosity are obtained at a lower sintering temperature than with stoichiometric TiC, but subsequent cladless hot isostatic pressing (HIP) is required to achieve 99 % density. High densities of 98 % accompanied by good mechanical properties become possible by pressureless sintering with the use of TiH2. MgO/Y2O3 doping also promotes densification but results in less transformable zirconia and increases the number and size of amorphous triple junctions. The consequences are a lower fracture toughness and strength.