Effect of La2O3 addition on microstructure and mechanical properties of TiC-based cermets

Rare earth (RE) oxides are typically used as dopants to improve the toughness of cermet materials. However, their effect on the cermet microstructure remains to be clarified. Towards this end, we used a vacuum sintering method to prepare the TiC-based cermets with different La2O3 contents (0.3 wt.% and 0.5 wt.%) and studied the cermet microstructures evolution by coupling experimental approaches and thermodynamic calculations. With the addition of La2O3, the ceramic phase in TiC-based cermets formed the black core-grey rim structure, where the undissolved La2O3 appeared at the edges of grey rims. In addition, an unanticipated solid-solution of La in the ceramic phase was observed, which helped to refine the particle size of the black cores and reduce the porosity of cermets. Correspondingly, the toughness and density were increased as a result of the well-developed grey rims around the black cores and the improved wettability between the ceramic and metallic phases. Thermodynamic calculations further unveiled that the solid-solution of La was inclined to occur in the ceramic phase rather than the metallic phase, while the incorporation of a trace amount of La could enlarge the temperature range of liquidphase sintering, facilitating the formation of grey rims following an iterative dissolution and precipitation process. Thus, the current work has described the effect of La on the microstructure and mechanical properties of TiC-based cermets, which may help guide the future developments of RE-containing cermets.